Skin Grafting and Reconstruction Techniques

In general, the simplest closure techniques are considered for problematic skin wounds, provided that the closure provides the appropriate durability and restores reasonable function to the area. Primary closure by apposition of skin margins normally is the simplest skin closure technique. Tension relieving techniques can be used to facilitate primary closure. In some cases, healing by contraction and epithelization is a practical option for wound closure, provided that this physiologic process can achieve the desired results in a timely fashion. There are occasions where open wound management can be more expensive than other surgical closure options. Skin stretchers, simple skin flaps, skin grafts, and axial pattern flaps are additional options for closing more challenging skin defects.

Anatomic Considerations

Preserving circulation is key to skin survival in wound management and closure. Direct cutaneous vessels are the primary vascular channels to the interconnecting cutaneous vascular network: the deep or subdermal plexus; middle or cutaneous plexus; and the superficial or subpapillary plexus (Figure 41-1). The elastic direct cutaneous arteries travel parallel to the overlying skin surface: they arborize to supply blood to the major capillary network, the subdermal plexus.^1,2
 

The direct cutaneous vessels and subdermal plexus reside in the hypodermal tissue layer beneath the dermis. Both are closely associated with the panniculus muscle layer, in areas where this cutaneous muscle layer exists. The major panniculus muscles include the cutaneous trunci, platysma, sphincter coli superficialis, and supramammarius muscles. This close relationship can be exploited to help preserve skin circulation during surgery.^1,2

Undermining Skin

Undermining skin is normally performed to facilitate the mobilization of the skin for wound closure and skin flap elevation. The following points should be considered to help preserve circulation to the skin:

1. Undermine skin below the panniculus muscle layer when present, to preserve the subdermal plexus and associated direct cutaneous vessels supplying the overlying skin.
2. Undermine skin, lacking a panniculus muscle layer (eg. middle, distal portions of the extremities) in the loose areolar fascial plane below the dermis.
3. Preserve direct cutaneous vessels encountered during undermining of the skin, if possible.
4. Elevate skin closely associated with an underlying muscle by including a portion of the outer muscle fascia with the dermis to preserve the subdermal plexus.
5. If possible, avoid or minimize the surgical manipulation of skin recently traumatized until circulation improves, as noted by the resolution of contusions, edema, and infection.

Avoid direct injury to the subdermal plexus by using atraumatic surgical technique. Sharp scalpel blades should be used to incise skin; avoid cutting skin with scissors. Skin hooks, stay sutures, Brown Adson forceps and DeBakey forceps can be used to manipulate the skin; avoid crushing instruments, including the use of Allis tissue forceps.^2-5

Technique Selection

Wound size and location usually dictates the technique(s) that should be considered for closure. The local availability of a loose, elastic skin will help determine if simpler closure techniques can be considered in a given case. Other potential sources of donor skin are then assessed. The primary goal is to restore function to the injured area, preferably with reasonable cosmetic results.⁵

Lower extremity wounds are particularly problematic due to the relative lack of circumferential skin. Wounds less than 90° circumference may close by second intention in some cases; the probability of contraction and epithelization decreases as the circumference of the defect increases.⁵

Clearly wounds approaching half or more of the limb’s circumference require closure with a skin graft or flap. By contrast, the trunk has variable amounts of loose, elastic skin to facilitate wound closure by second intention, skin advancement, flaps, or simply by applying skin stretchers. In many cases, skin stretchers are simpler and more effective to use for closure of moderate to large skin defects.⁵

Although open wound management may be both practical and economical in managing many wounds, costs can add up especially in those cases where contraction and epithelization is slow. Bandages, dressings, topical agents, and recheck appointments cumulatively can approach or exceed surgical closure. Periodic reassessment of the wound, and clear communication can eliminate misunderstandings that occasionally occur with the pet owner. Flap and/or graft closure may be reserved for those wounds where 2nd intention healing fails to make significant gains in wound closure.⁵

Unlike humans, skin flaps generally are considered a more practical method to close problematic wounds in veterinary medicine; in human reconstructive surgery skin grafts are often preferred. Skin grafts are most useful for the more problematic lower extremity defects, and large surface area wounds where flaps and skin stretchers are not practical options.⁵

Skin Flaps (Pedicle Grafts)

A skin flap is an elevated portion of skin and subcutaneous tissue with a vascular attachment to the body. The base or pedicle of the flap may be a cutaneous attachment (with its intact capillary network), or an “island” segment of skin tethered by a single direct cutaneous artery or vein. Flaps also may be elevated with an underlying muscle which provides a source of circulation though interconnecting vascular channels: they are termed myocutaneous or musculocutaneous flaps.^3,5

Skin flaps are particularly useful in small animals, allowing the veterinarian to utilize local or regional loose skin for closure of problematic wounds. They can be transplanted into areas devoid of circulation, unlike skin grafts which rely on revascularization from underlying healthy vascularized tissues for survival. Because the complete dermis and hypodermis are present, skin flaps have excellent durability and hair growth. Properly developed and transferred, skin flaps do not require the more elaborate bandage protection and immobilization needed for skin graft survival.^3,5

Pedicle grafts can be classified according to their (1) type of circulation; (2) location in relation to the recipient (wound) bed; and (3) tissue composition (eg., myocutaneous flaps, compound/ composite flaps). Most skin flaps are based on the subdermal plexus circulation (subdermal plexus flap) (Figure 41-2) incorporation of a direct cutaneous artery and vein results in the formation of an axial pattern flap (Figure 41-3). A variation of the axial pattern flap is the island arterial flap, in which the entire skin flap is detached from the body, but tethered by a paired direct cutaneous artery and vein (Figure 41-4). Because of their excellent blood supply, axial pattern flaps can be developed of greater dimensions for closing sizeable skin wounds.^3,5-7

Flaps elevated immediately adjacent to the recipient bed are termed local flaps, whereas flaps elevated from a more remote location are termed distant flaps. Flaps made adjacent to a wound are technically easier to perform, provided that sufficient skin is available for their development. Distant flaps normally are more difficult to elevate and transfer. Historically distant flaps have been classified according to the method of transferring the skin to a given wound, including: delayed tube flap (indirect flap); elevation of the affected limb beneath a flap created on the trunk (direct flap). Axial pattern flaps have largely precluded the routine use of these more labor-intensive distant flap techniques. Similarly, most distal extremity wounds are better managed with skin grafts.^3,5-9
 

Flaps need not be exclusively comprised of skin or mucosa alone. As noted above, skin flaps also can be elevated with an underlying muscle segment, creating a myocutaneous flap (Figure 41-5). Flaps comprised of two or more tissues are called compound or composite flaps. Muscle, bone and cartilage also may be included in these flaps.^3,5,10 For example, a full-thickness labial flap is comprised of mucosa, skin, and a central musculofascial layer. Oral composite flaps are useful for oral and nasal reconstructive surgery. However, these more specialized flap techniques are less commonly used compared to skin flaps and grafts for wound closure.⁵
 

General Principles of Flap Development

The wound size, location, shape, and condition dictate the technique(s) required to close the defect. In general, surgeons try to used the simplest, most direct technique to close the wound and restore function to the area.^3,5

The elastic properties of the skin are assessed adjacent to the wound. Ideal donor areas have ample skin available to elevate a flap and close the donor bed under minimal tension. The scrotum also has been used to close adjacent wounds by flap advancement or rotation into the wound.¹¹ There are occasions where wound closure to protect an important anatomic structure may take precedent over creating a donor defect that cannot be closed after transposing the flap.⁵

The size of the wound will dictate the size of the skin flap required to close most, if not all of the defect. In some cases, partial wound closure with a skin flap may be sufficient to successfully close the recipient bed, with the assistance of 2nd intention healing for the remaining portion of the area. If there is insufficient healthy skin available for local flap development, axial pattern flaps, skin grafts, and skin stretching options are considered.⁵

Flap orientation is considered both for the relative ease of transference and the positioning of the pedicle for optimal circulation. Factors that help preserve circulation to a flap include: (1) the base of the flap should be equal to or slightly wider than the uniform width of the flap (island arterial flaps are an exception); (2) the flap length should be kept to the minimum required to close the wound without undue tension. However, simply increasing the width of a flap does not increase the total length of survival, unless direct cutaneous vessels are incorporated into the pedicle.

It is preferable to orient a subdermal plexus flap’s base in the direction of a direct cutaneous artery/vein if possible. With few exceptions, necrosis associated with a skin flap is the result of insufficient circulation to sustain the tissue.^3,5

Wound (Recipient Bed) Preparation

The recipient bed should be free of debris, necrotic tissue, and infection prior to closure. Unlike free grafts, skin flaps can survive over defects which have little or no circulation. Chronic granulation tissue can be resected at the time of flap closure. In some cases, the fibrotic and contaminated tissue can be removed, allowing for a healthy granulation bed to form within 3 to 5 days, thereby creating a more suitable wound surface for flap application. The epithelialized wound borders also are removed, thereby enabling the surgeon to close the defect completely with the skin flap.^3,5 Chronic radiation beds can be problematic to close, as a result of a dramatic decline in circulation over time. Skin flaps, muscle flaps, and myocutaneous flaps are options to close these wounds, provided that the vascular pedicle is preserved.⁵

Surgical Techniques

Local Flaps

Local flaps remain as one of the most simple and practical methods of closing small to moderate sized problematic wounds. Their effective use requires loose, elastic skin adjacent to the wound as a donor source for flap development. Local flaps normally are based on the subdermal plexus circulation. As noted, flaps must be kept as short as possible to help assure that perfusion can reach the terminal end of the flap. Local flaps are broadly classified as advancement flaps or rotating flaps. Local flaps can be developed in most body regions, although their use is somewhat limited in the lower extremity regions. The axillary and inguinal skin folds can be used in a similar fashion.^12,13 The following are the most useful local flaps to consider on a routine basis.^3,5

Single-Pedicle Advancement Flap

The single-pedicle advancement flap (sliding flap) is simple in design and execution. The width of the flap approximates the width of the defect. Their effective use requires the flap to advance or stretch directly into the defect. The advanced flap simultaneously closes both the donor and recipient beds.^3,5

To create a single-pedicle advancement flap, two skin incisions equal to the width of the wound are made in a staged or incremental fashion. In general, it is useful to have the two incisions slightly diverge to assure that the base of the flap is not inadvertently created too narrow thereby compromising circulation. The distant edge of the flap, bordering the wound is gently grasped, elevated, and the flap undermined. The process is continued until the flap stretches (advances) over the recipient bed. In most dogs and cats, 3-0 monofilament suture material is used to secure the flap (Figure 41-6).⁵

As noted, the length of the flap should be kept to the minimum in order to close the wound without excessive tension. Two shorter single-pedicle advancement flaps, on opposing sides of the wound, can be used to close longer defects. Termed “H-Plasty” two shorter flaps may close the wound without resorting to a single, longer advancement flap (Figure 41-7).⁵

The primary problem associated with advancement flaps is their reliance on stretching over the wound. There is a tendency for elastic retraction by the collagen fibers in the flap’s dermis. This can contribute to postoperative distortion in some clinical situations. For example, advancement flaps, used to close problematic eyelid wounds, occasionally will distort the lid margin resulting in an unsatisfactory result both cosmetically and functionally.

Under these circumstances, a 90° transposition flap should be considered, since this rotating flap closes wounds by “donating” additional skin to the immediate area.^3,5
 

Bipedicle Advancement Flap

A bipedicle advancement flap is created by making two parallel incisions and undermining the skin segment: the flap is advanced at a right angle to its long axis. Bipedicle flaps are usually considered for closing adjacent elongated wounds. Although circulation is derived from two pedicles, long release incisions may result in a more centrally located “ischemic zone” with necrosis. If sufficient skin is present, the donor area can be closed (Figure 41-8).^3,5

The release or relaxing incision in design and execution is a bipedicle advancement flap. Release incisions are used to reduce tension on an adjacent incision. Used in this fashion, the release incision is left open to heal by second intention. Release incisions may be little more than 1 or 2 centimeter “stab wounds” or extended several centimeters to close a problematic skin wound. As a general rule release incisions are no closer than 3 to 5 centimeters from incision.⁵
 

Transposition Flap

A transposition flap is a rectangular pedicle graft that pivots into position. Normally transposition flaps are rotated at a 45° to 90° angle in relation to the long axis of the skin defect. Flaps can be transposed at an angle greater than 90° although the flap length will shorten with this greater arc of rotation. One border of the flap generally contacts the wound border (Figure 41-9). Transposition flaps can be developed in most body regions, although their size is somewhat limited in the mid- to lower extremities.⁵
 

Flap width approximates the width of the “rectangular” shaped defect; the flap length is measured from the pivot point of the flap base to the most distant point of the defect (Figure 41-10). To reduce tension, a stab or release incision may be created along the line of greatest tension. Alternatively, a release incision can be created in the skin adjacent to the defect, thereby eliminating the need to incise the flap. In practice, I will measure flaps with the above dimensions. In many cases, I will shorten the calculated length of the flap if possible, thereby improving the chance that reasonable perfusion can nourish the terminal flap border.^3,5
 

Z-Plasty

Z-plasty, by design, is a variation of the transposition skin flap. A “Z” shaped incision is created with the central limb of the “Z” placed parallel to, and overlying a problematic tension band. When each flap is transposed into their opposing donor beds, wound closure is achieved while modestly reducing tension in the immediate area. In veterinary medicine, Z-plasty is primarily used to reduce incisional tension or lengthen a restrictive scar band. In humans, Z-plasties (and its variation, W-Plasty) are used to cosmetically mask linear scars.⁵ Use of multiple small z-plasties is not considered very effective for lengthening restrictive scars.

The basic design employed is creating a Z-shaped incision at 60° angles to the central limb of the “Z.” Each incision is equal in length. The key to understanding Zplasty is the following: the central limb is aligned parallel to, and overlying the “line of tension.” The net gain in length theoretically is 75% of the length of the central limb, after each triangular flap is transposed in opposite directions. In practice, the net gain is closer to 50%. In figure 41-11, z-plasty is employed to lengthen a restrictive scar.

Similarly, this Z-plasty technique can be used to lengthen a local area of skin tension to facilitate incisional closure (for example, a portion of a skin incision, after tumor removal, cannot be closed due to regional skin tension). The incisional gap is determined in centimeters. To lengthen this line of tension, a Z-plasty incision 5-10 centimeters from the incision with the central limb of the “Z” aligned over the tension “band.” For example, to obtain a 3 centimeter gain, the Z-plasty central limb is aligned to this zone of tension with each incision 6 centimeters long. The Z-plasty is created, the problematic incision in closed, and each triangular flap is sutured into their transposed position}.⁵

The author prefers skin stretchers, the 90° transposition flap, and release incisions to relieve skin tension. However, some surgeons find the Z-plasty useful and effective for reducing incisional tension as described above.
 

Axial Pattern Flaps

Axial pattern flaps receive a major source of their circulation by incorporating a direct cutaneous artery and vein into the flap’s pedicle. As a result large skin flaps can be created with greater assurance of flap survival, provided the vessels are preserved.^3,5 There have been several papers describing the use of axial pattern flaps in the more recent veterinary literature describing the use of the lateral thoracic artery and superficial temporal artery in the dog and cat.^14-16 Other papers have described the use of various axial pattern flaps in wound closure with their clinical outcome.^17-20 Table 41-1, summarizes the major axial pattern flaps most commonly used in the dog and cat (Figures 41-12 and 41-13).^3,5,22-29

Careful positioning of the patient is necessary for outlining each flap, using marking pens: skin distortion in relation to anatomic landmarks used for flap may result in failure to incorporate the vessels.^3,5 Axial pattern flaps can be rotated into a variety of wounds. On occasion the flap must cross over skin interposed between the donor and recipient sites. A “bridge incision” or partial tubing of the flap may be used to cross over this area. The flap may be shaped in the standard rectangular (peninsular design) shape or modified with a right angle (hockey-stick variation) for closure of wider or irregular problematic wounds.⁵

Axial pattern flaps may be converted to an island arterial flap, by cutting the cutanenous pedicle.^3,5 Tethered by the direct cutaneous artery and vein, the mobile island flap can be pivoted 180° into a defect. This technique is normally reserved to close large skin wounds that encroach on the normal base of the flap, thereby creating an island arterial flap by “default.” Surprisingly, the survival area of island arterial flaps and axial pattern flaps is nearly identical.^24,30 A variation of this technique, the neovascular island flap has been reported in the dog for closure of small trophic ulcers of the paw.³¹

The thoracodorsal and caudal superficial epigastric axial pattern flaps are the most versatile in the dog and cat, based on their length and arc of rotation (See Figures 41-12 through 41-15). Nonetheless, the other axial pattern flaps provide a wide array of options for the veterinary surgeon to consider for closing wounds secondary to trauma or tumor removal.^{5,26,32,33,34}

Compound and Composite Flaps

Although musculocutaneous (myocutaneous) flaps can be used to close skin defects, they may be better suited for closure of problematic wounds where muscle “padding” may be beneficial. The latissimus dorsi muscle, alone or as a myocutaneous flap, can be used for thoracic wall reconstruction. It also can be used to cover problematic elbow ulcers, providing padding over this bony prominence (Figures 41-14 and 41-15). The cutaneous trunci myocutaneous flap is better suited to exclusive wound closure, although the adjacent thoracodorsal axial pattern flap is better suited to closing the larger wounds within their respective arcs of rotation.⁵

Secondary or revascularized myocutaneous flaps can be created by grafting skin onto a muscle; once healed, the muscle is elevated and the composite flap transferred into a local defect as a flap or free flap [microvascular transfer].^35-40 Performed successfully under research conditions, they have limited clinical practicality over the flap and graft options already discussed.

Composite flaps have been successfully used for facial reconstruction, including the labial advancement flap, buccal rotation technique, labial lift-up bipedicled composite flap, and variations of these procedures.⁵ In one case, a composite flap, using a damaged portion of the ear, was used to close a large adjacent defect.⁴¹ A composite mucocutaneous subdermal plexus flap employing the upper lip (“lip to lid procedure”) has been successfully used for full-thickness eyelid reconstruction in the dog and cat.^42,43 These compound or composite flaps are useful for specific body defects and are not routinely employed for skin defects alone.
 

Skin-Stretching Techniques

Skin is a nonhomogeneous viscoelastic tissue with the combined characteristics of a viscous fluid and elastic solid. Three factors account for skin extensibility as a stretching force is applied: (1) progressive straightening of dermal collagen convolutions; (2) Parallel alignment of dermal collagen fibers; (3) extension of fully aligned collagen fibers with increasing stretching force applied to the skin.⁴³

Skin in various regions of the body has its own natural or “inherent extensibility”. This is assessed by grasping and lifting the skin, a procedure all surgeons perform when assessing wound closure options. Mechanical creep is the biomechanical property that enables skin to extend or stretch beyond the limits of its inherent extensibility. As a stretching force is applied to the skin over time, collagen fibers align with the applied tension; collagen fibers compact and slowly displace interstitial fluid during the process. As the skin stretches beyond the limits of its natural extensibility over time, stress relaxation occurs. Stress relaxation refers to the progressive decrease in the force required to maintain the length of the stretched skin. For skin to stretch beyond the limits of its natural extensibility, the skin best deforms from the application of a constant load or force over time. Similarly intermittent application of force or “load cycling” also can assist in the process of skin stretching. A natural variation of this phenomenon is “biologic creep”, or the progressive increase in cutaneous surface area noted as a result of expansile masses located beneath the skin.⁴⁴

There are a few techniques that are currently used to stretch skin in humans and small animals, to facilitate wound closure. They include tissue expanders; presuturing; and an elastic cable system developed by the author, termed “skin stretchers.^5,44”

Skin Expanders

Skin expanders are inflatable devices composed of an expandable silicone elastomeric bag or reservoir; an attached silicone tube is connected to a self-sealing injection port. The entire device is placed beneath the skin. Controlled inflation of the device is accomplished by injecting sterile saline; a hypodermic needle is inserted into the palpable injection port, through the overlying skin. The surface area of the overlying skin is gradually stretched, increasing its surface area by mechanical creep and stress relaxation. Once fully expanded, the skin is advanced or pivoted into a regional defect.^5,45-47

Effective use of tissue expanders requires a reservoir of sufficient size to exert their stretching effect over on the overlying skin. However, they do require a degree of skin laxity for creating a pocket of sufficient size to accommodate the mass of the collapsed device. As a result, they are better suited for small to moderate sized problematic skin defects of the middle to distal aspects of the extremities. They may have limited use for closure of difficult wounds of the head. Many surgeons consider alternative means of closing extremity wounds, including skin grafts and select skin flap techniques. Veterinarians normally hesitate in purchasing a tissue expander for several hundred dollars with limited or no experience in their use. Properly handled, silicone tissue expanders can be autoclaved and reused.^5,45-47

Implant size and shape is determined by the dimensions of the skin defect. Normally the surface area of the thick reservoir base corresponds to the surface area gain expected. Alternatively, slightly smaller reservoirs can be used, but hyperinflated 20- to 25% above the designated capacity of the device. Two smaller expanders also can be used in some situations. In one canine study, the rectangular 100 cc tissue expander appeared to be well suited for use in medium sized dogs.^5,45

Variable rates of inflation have been used in human surgery. Although a somewhat slower rate of expansion may be reduce the risk of abrupt circulatory compromise to delicate skin, more rapid expansion rates may be preferable in other situations. Canine research demonstrated that 100 ml expanders can be inflated with minimal complications within 2 weeks, using an alternate-day injection schedule. A more cautious (3 week) rate may be advisable for delicate skin or tissues previously compromised by trauma. Use of expanders in previously irradiated tissues is best avoided.^5,45

Outpatient visits enable the veterinarian to assess the skin during saline infusion. In human patients, the skin is assessed for color change (blanching, cyanosis) and patient discomfort. I have not noted these changes in the dog. During the later phase of expansion, skin tension can be pronounced immediately after the injection. When reassessed at the time of the following injection, skin tension has decreased. Viability of the skin is highlighted by the unimpeded growth of hair in the expanded skin.^5,45

Upon completion of the expansion process, the expanded skin can be advanced or rotated into the recipient bed, usually in the form of a pedicle graft. This must be carefully planned in advance, since the initial access incision for implantation of the expander should not be incorporated into the base of the proposed flap (Figure 41-16).^5,45
 

Skin Stretchers

Developed by the author, skin stretchers are an external device used to stretch skin rapidly, by the processes of mechanical creep and stress relaxation previously discussed. They are particularly effective for closing moderate to large wounds involving the trunk, neck and neighboring cranial area; they have limited use in the mid- to distal extremities. Skin stretchers enable the surgeon to close problematic wounds without the need for skin grafts or skin flaps.^5,34,44 They are my preferred method of choice to close most large skin wounds of the thoracic and abdominal areas.^5,44

Skin stretchers have two components; skin pads to which elastic cables are affixed. The present design uses Velcro hook pads for the skin pads, and specially designed one inch elastic cable covered by Velcro “felt.” Pads are placed on opposing sides of a wound and are secured to the skin with cyanoacrylate glue. Cables are applied to the opposing pads under moderate tension. Cable tension is gradually increased every 6 to 8 hours for 48 to 72 hours prior to surgical closure of the defect. At the time of surgery, pads can be pulled off the skin. Left in place, skin pads normally loosen within 7 to 10 days of application, as a result of normal skin desquamation. Nail polish remover is a solvent for cyanoacrylate glue, although the author has not used it to facilitate skin pad removal (Figure 41-17).^5,44

The primary complication is the occasional need to replace a skin pad that displaces as cable tension increases during their 48 to 72 hours of application. Pads are reglued or replaced until completion of the stretching procedure. Because the skin tension is applied over the wide footprint of the skin pads, patient comfort is maintained and allows for more forceful application of cable tension. The skin stretcher system can be used to prestretch skin prior to elective surgical procedures, including the surgical removal of problematic skin tumors. Skin stretchers are also very effective in minimizing incisional tension after wound closure; pads and cables can be used for 3 to 5 days to help prevent wound deshiscence.^5,44
 

Free Skin Grafts

Free skin grafts lack a vascular attachment on transfer to the recipient graft bed. As a result, their initial survival at the time of transplantation is by absorbing tissue fluid (plasmatic imbibition) from the recipient bed capillary circulation is established from the vascular wound bed. Initial reestablishment of circulation to the free graft is noted approximately 48 hours after application. During this period, capillaries from the recipient bed establish contact with the exposed vascular channels (exposed graft plexuses) to reestablish vital circulation. Termed “inosculation,” reestablishment of vascular flow will give the skin graft a pink coloration. Grafts with a lavender color are the result of venous congestion; they assume a pink hue as circulation improves. The thickness of the graft will determine whether the superficial, middle or deep (subdermal) plexus is exposed to the underlying vascular bed. The finer vascular network of the superficial plexus has a greater chance at revascularization, a major reason why thin split-thickness skin grafts have a greater likelihood of vascularization. Similarly, a medium split-thickness skin graft has a greater likelihood of revascularization compared to a full-thickness graft. Despite these earlier research findings, properly prepared, full-thickness skin grafts have an excellent chance of surviving or “taking.^5,48”

Once initial contact (inosculation) occurs between the capillary buds and exposed vascular channels of the skin graft, the capillaries grow into the graft and remodel the capillary network over the next several days. However, there are several factors that may delay or prevent revascularization of a skin graft, resulting in necrosis. Any accumulation of material between the graft and recipient bed can block inosculation, including pus, blood (hematoma), serum, or foreign material. Grafts techniques that provide effective drainage, can reduce the probability of graft loss from this potential complication.^5,48

Subcutaneous fat must be removed from full-thickness skin grafts; presence of the fatty tissues will prevent revascularization of the free graft. The graft must conform to the contour of the wound bed: excessive stretching of the graft will create a “drum skin” over depressions in the recipent bed, preventing revascularization. Folds or wrinkles in the graft will have a similar effect. Lastly, grafts must be immobilized to prevent motion between the recipient bed and overlying graft: shearing forces will prevent revascularization.⁵

Skin staples or sutures are frequently used to secure skin grafts to the recipient area. Fibrin deposition between the graft and underlying recipient bed serves as a natural glue to help stabilize the graft. The fibrin serves as a scaffold for fibroblasts and subsequent collagen deposition. A protective bandage is required to prevent motion to the area during the healing process.⁵

As noted, a healthy vascular wound bed is required for graft survival. Healthy granulation tissue, viable muscle, and periosteum are capable of supporting a skin graft. Chronic granulation tissue is laden with collagen and has an unsatisfactory blood supply to support a graft. In many cases, this tissue may be excised, promoting reformation of a healthy granulation bed within 5 days. Chronic radiation ulcers lack the circulation to support a skin graft. In wounds lacking sufficient circulation to support a graft, a skin flap or muscle flap (covered with a skin graft) may be necessary.⁵

Skin Graft Classifications

Free grafts can be classified according to the source of the graft, its thickness, and its shape or design. Autogenous grafts are used exclusively for permanent coverage in dogs and cats. Allografts (homografts) and xenografts (heterografts) are rarely used in veterinary medicine as a temporary biologic dressing: left in place, these grafts are eventually rejected by the patient’s immune system. Isografts, or the exchange of skin grafts between highly inbred strains of animals is usually limited to research rats and mice.^5,48

Free grafts are commonly classified according to the thickness of the graft. Full-thickness skin grafts include the entire dermis, thereby retaining a large percentage of the compound hair follicles. Split-thickness skin grafts, harvested by a graft knife, razor blade, or dermatome include variable portions of the dermis. They are broadly classified as thin, medium, or thick split thickness skin grafts. Thinner grafts have relatively few hair follicles and are less cosmetic in fur-bearing animals, unlike the human. Although thin split thickness grafts reportedly survive or “take” more readily, they also lack the hair growth and overall durability of full-thickness skin grafts. Split-thickness grafts, harvested with a dermatome, normally are reserved for large wounds (especially large full-thickness bums) with more limited donor skin.^5,48,49

Surgical Techniques

Free grafts are most commonly used for the more problematic defects involving the lower extremities. Most surgeons will use full thickness grafts when possible due to the superior hair growth, durability and relative ease of harvesting. Full thickness skin grafts can be harvested and applied as a “sheet” or cut into various shapes including punch-pinch grafts, strip grafts, stamp grafts, or mesh grafts (Figures 41-18 through 41-21).

Punch, pinch, strip, and stamp grafts afford partial coverage of a wound surface. The space between grafts provides drainage as their epithelial cells migrate over the exposed granulation tissue. Grafts that provide reasonable drainage are more likely to survive in the presence of a low-grade bacterial infection. Punch and pinch grafts are easy to perform and are used most commonly to promote epithelization of smaller, slow healing open wounds. However, depending on their numbers and spatial relationship, they do not provide a particularly durable epithelial surface for those body regions subject to periodic external trauma. Full-thickness mesh grafts are better suited for larger wounds.The techniques for punch, strip, and stamp grafts are described in (See Figures 41-18 through 41-21).⁵

Full-thickness mesh grafts are especially useful for coverage of larger wounds involving the distal extremities (See Figure 41-21). An impression template of the moist wound surface can be performed using gauze or absorbable paper [the paper packaging for sterile gloves is an ideal material]. Using sterile materials, the template can be trimmed and directly applied to the donor area. In most cases, skin is simply harvested from the lateral thorax and abdomen. The template is placed on the donor area, ideally allowing for the graft to be harvested with the appropriate hair growth pattern of the recipient area. Normally, I will harvest an additional one centimeter around the circumference of the template. Harvesting of the graft as a simple geometric pattern that includes the footprint of the template [rectangular design is most commonly used] will facilitate closure of the donor area; the graft can be trimmed to the appropriate size at the time of application.⁵
 

A key step in full thickness graft preparation is the removal of all subcutaneous tissues (fat, panniculus muscle) down to the dermal surface of the graft. Unless removed, this layer of tissue will prevent revascularization of the graft. Properly “defatted”, the dermal surface of the graft will have a “cobble stone” appearance: dermal collagen striations and the speckled appearance of compound hair follicles are identifiable on close inspection (Figure 41-22).⁵

Grafts can be directly abutted against the borders of the skin defect and sutured into position. Alternatively, the author prefers to slightly overlap the wound margins of the recipient bed with the graft. This facilitates securing the graft with sutures or skin staples while completely covering the wound. Skin staples facilitate graft application by rapidly securing the graft to the overlapped cutaneous borders. Graft tension is adjusted by stapling one side and slightly stretching the graft before stapling the opposing border. The process is repeated in the opposite plane. The graft is applied with sufficient tension to allow the graft to flatten and conform to all surface areas. Graft holes are stretched to allow a gap of a few to several millimeters to form, facilitating drainage. As a general rule, grafts are not sutured to the wound bed in order to avoid hemorrhage. If the graft is tenting over a depression, a fine suture can be used to assure proper graft to bed contact. Fibrin deposition occurs several hours after application, forming a natural glue to immobilize the graft. Skin sutures or staples can be removed in 7 to 10 days; the overlapped skin border will undergo necrosis and can be trimmed off at this time.⁵
 

Pad Grafting

There are several articles discussing the use of pad grafts to replace the loss of the metacarpal and metatarsal pads, with the simultaneous loss of the digital pads. With the presence of the adjacent toes, digital pad flaps can be used to reconstruct the metacarpal/metatarsal pads more effectively.^5,50-52

Grafts: Postoperative Care

Proper protection and immobilization is essential to graft survival. It is preferable to confine the patient to a cage. Sedation may be advisable for hyperactive patients.

A nonadherent dressing covered with a thick layer of bland ointment [triple antibiotic ointment is economical to use] is applied to the grafted area.and stapled over the area to prevent displacement. This is followed by layers of sterile gauze pads, and self-adherent roll gauze alternated with cast padding. A firm, thick bandage is formed prior to application of an outer elastic wrap. To further immoblize the area, tongue depressors, aluminum bars, half casts, metasplints, slings, and Shroeder-Thomas splints may be employed. The Latter splint is especially useful for immobilizing the knee, elbow, and tibiotarsal joints. Spica splints/bandages are advisable to immobilize the upper extremity, especially in cats, whose reputation for extricating themselves from bandages is legendary.^5,48

The author prefers to change the initial bandage 3 to 5 days postoperatively. Bandages can be changed 48 hours after surgery, but in this early period there is a risk of displacing the graft and damaging the fragile reestablished blood supply. Adherent dressings occasionally adhere to the grafted area. Saline can be applied to facilitate its removal, although it is more prudent to apply additional ointment to the area and rebandage the area. The exposed graft is inspected for viability and signs of infection. A culture can be taken if infection is suspected.⁵

Early signs of graft necrosis are discouraging but not always catastrophic: hair follicles in the deeper dermal layer of the graft may survive and serve as a source for epithelization. Subsequent bandage changes may be performed every 2 to 4 days, depending on the condition of the graft. This routine is continued for approximately 2 weeks or until epithelization is complete. This can be followed by application of a lighter bandage for an additional 10 to 14 days, if necessary. An Elizabethan collar is advisable to prevent self-mutilation of the graft site. Eventually, the owner can remove the collar temporarily with the pet under close supervision. If the patient does not rub or lick at the grafted area, the collar can be eliminated completely, usually within a month after the surgery.⁵ Bandages can have adverse effects on the graft. Excessive bandage tension and pressure points from uneven bandage application can result in partial or complete graft failure. Bandages also can have an abrasive effect on the graft if immobilization of the affected area is inadequate.⁵

References

1. Pavletic MM. The Vascular supply to the skin of the dog; a review. Vet Surg 1980;9:77.
2. Pavletic MM. The integument. In: Slatter DH, ed. Textbook of small animal surgery, 3rd ed. Philadelphia: WB Saunders, 2003.
3. Pavletic MM. Pedicle grafts. In: Slatter DH, ed. Textbook of small animal surgery, 3rd ed. Philadelphia: WB Saunders 2003.
4. Pavletic MM. Underming the skin in the dog and cat. Mod vet Pract 1986;67:16.
5. Pavletic MM. Atlas of small animal reconstructive surgery, Philadelphia: WB Saunders, 1999.
6. Pavletic MM. Caudal superficial epigastric arterial pedicle grafts in the dog. Vet Surg 1980;9:103.
7. Pavletic MM. Canine axial pattern flaps, using the omocervical, thoracodorsal, and deep circumflex iliac direct cutaneous arteries. Am J Vet Res 1981;42:391.
8. Alexander JW, Hoffer RE, MacDonald JM. The use of tubular flap grafts in the treatment of traumatic wounds on the extremity of the cat. Feline Pract 1976:6:2.
9. Yturraspe DJ, Creed JE, Schwach RP. Thoracic pedicle skin flap for repair of lower limb wounds in dogs and cats. J Am Anim Hosp Assoc 1976;12:581.
10. Pavletic MM, Kostolich M, Koblik P, et al. Comparison of the cutaneous trunci myocutaneous flap and latissimus dorsi myocutaneous flap in the dog. Vet Surg 1987:16:283.
11. Matera JM, Tatarunas AC, Fantori DT, asconcellos CNC. Use of scrotum as a transposition flap for closure of surgical wounds in three dogs. Vet Surg 2004;33:99.
12. Hunt GB, Tisdall PLC, Liptak JM, et al. Skin fold advancement flaps for closing large proximal limb and trunk defects in two dogs and cats. Vet Surg 2001:30:440.
13. Hunt GB. Skin fold advancement flips for closing large sternal and inguinal wounds in cats and dogs. Vet Surg 1995;24:172.
14. Anderson DM, Charlesworth TC, White RAS. A novel axial pattern flap based on the lateral thoracic artery in the dog; lateral thoracic skin flap. Vet Comp Orthop Traumatol 2004;17:57.
15. Fahie MA, Smith MM. Axial pattern flap based on the cutaneous branch of the superficial temporal artery in dogs: An experimental study and case report. Vet Surg 1999;28:141.
16. Fahie MA, Smith MM. Axial pattern flap based on superficial temporal artery in cats; an experimental study. 1997;26:86.
17. Aper R, Smeak D. Complications and outcome after thoracodorsal axial pattern flap reconstruction of forelimb skin defects in 10 dogs, 1989-2001. Vet Surg 2003;32:378.
18. Lidbetter DA, Williams FA, Krahwinkel OJ, et al. Radical lateral body-wall resection for fibrosarcoma with reconstruction using polypropylene mesh and a caudal superficial epigastric axial pattern flap: a prospective clinical study of the technique and results in six cats. Vet Surg 2002;31:57.
19. Lester S, Pratschke K. Certral hemimaxillectomy and reconstruction using a superficial temporal artery axial pattern flap in a domestic short hair cat. Fel Med Surg 2003;5:241.
20. Stiles J, Townsend W, Willis M, et al. Use of a caudal auricular axial pattern flap in three cats and one dog following orbital exenteration. Vet ophthal 2003;6:121.
21. Smith MM; Carrig CB, Waldron DR, et al. Direct cutaneous arterial supply to the tail in dogs. Am J Vet Res 1992;53:145.
22. Kostolich M, Pavletic MM. Axial pattern flap based on the genicular branch of the saphenous artery in the dog. Vet Surg 1987;16:217.
23. Pavletic MM, Macintire D. Phycomycosis of the axilla and inner brachium in a dog: surgical excision and reconstruction with a thoracodorsal axial pattern flap. J Am Vet Med Assoc 1982;180;1197.
24. Henney LHS, Pavletic MM. Axial pattern flap based on the superficial brachial artery in the dog. Vet Surg 17:311, 1988.
25. Sardinas JC, Pavletic MM, Ross JT, et al. Comparative viability of penisular and island axial pattern flaps incorporation the cranial superficial epigastric artery in dogs. J Am Vet Med Assoc 1995;207:452.
26. Remedios AM, Bauer MS, Bowen CV. Thoracodorsal and caudal superficial epigastric axial pattern skin flaps in cats. Am J Vet Res 1992;53:145.
27. Smith MM, Payne JT, Moon ML, et al. Axial pattern flap based on the caudal auricular artery in dogs. Am JVet Res 1991;52:922.
28. Pavletic MM, Wafters J, Henry RW, et al. Reverse saphenous conduit flap in the dog. J Am Vet Med Assoc 1982;182:380.
29. Cornell K, Salisbury K, Jakovljevic S, et al. Reverse saphenous conduit flap in cats: an anatomic study. Vet Surg 1995;24:202.
30. Milton SH. Experimental studies of island flaps. I. The surviving length. Plast Reconstr Surg 1971;48:574.
31. Gourley IM. Neurovascular island flap for treatment of trophic metacarpal pad ulcer in the dog. J Am Anim Hosp Assoc 1978;14:119.
32. Pavletic MM. Surgery of the skin and management of wounds. In: Sherding R, ed. Diseases of the cat: diagnosis and management. New York: Churchill Livingstone, 1994.
33. Lascelles BDX, White RAS. Combined omental pedicle graft and thoracodorsal axial pattern flaps for the reconstruction of chronic nonhealing wounds in cat. Vet Surg 2001;30:380.
34. Mayhew PD, Holt DE. Simultaneous use of bilateral caudal superficial epigastiric axial pattern flaps for wound closure in a dog. Sm Anim Pract 2003;44:534.
35. Krizek TJTani T, Desprez JD, et al. Experimental transplantation of composite grafts by microsurical vascular anastomoes. Plast Reconstr Surg 1965;36:358.
36. Tsai TJ et al. The effect of hypothermia and tissue perfusion on extended myocutaneous flap viability. Plast Resconstr Surg 1982;70:444.
37. Harii K, Ohmori K, Sekiguchi J. The free musculocutaneous flap. Plast Reconstr Surg 1973;57:294.
38. Schlenker JD. Discussion: the effect of hypothermia and tissue perfusion on extended myocutaneous flap viability. Plast Reconstr Surg 1982;70:453.
39. Erol 00, Spira M. Secondary musculocutaneous flap: an experimental study. Plast Reconstr Surg 1980;65:277.
40. Schechter GL, Biller HF, Ogura JH. Revascularized skin flaps: a new concept in transfer of skin flaps. Laryngoscope 1969;79:1647.
41. Swanson SW, Goring RI, Dehann JJ, et al. Reconstruction of a facial defect using the ear pinna as a composite flap. J Am Animal Hosp Assoc 1998;34:399.
42. Pavletic MM, Nafe LA, Confer AW. Mucocutaneous subdermal plexus flap from the lip for lower eyelid restroration in the dog. J Am Vet Med Assoc 1982;180:921.
43. Hunt GB. Use of the lip to lid flap for replacement of the lower eyelid in cats. Vet Surg 2006;35:284.
44. Pavletic MM. An external skin-stretching device for wound closure in dogs and cats. J. Am Vet Med Assoc 2000; 217:350.
45. Spodnick G, Pavletic MM, Schelling S, et al. Controlled tissue expansion in the distal extremities of dogs. Vet Surg 1993;22:436.
46. Keller WG, Anon DN, Rarich PM, et al. Rapid tissue expansion for the development of rotational skin flaps in the distal portion of the hind limb of dogs: an experimental study. Vet Surg 1994;23:31.
47. Johnston DE. Tissue expanders. Vet Clin No Am. 1990;20:227.
48. Swaim SF, Henderson RA. Small animal wound management. Philadelphia Williams and Wilkins, 1997.
49. Bradley DM, Swaim SF, Alexander CM, et al. Autogenous pad grafts for reconstruction of a weight - bearing surface: a case report. J Am Anim Hosp Assoc 1994;30:533.
50. Aragon CL, Harvey SE, Allen SW, Stevenson MA. Partial thickness skin grafting for large thermal skin wounds in dogs. Compen Contin Edu 2004;26;2005.
51. Pavletic MM. Foot salvage by delayed reimplantation of severe metatarsal and digital pads using a bipedicle direct flap technique. J Am Anim Hosp Assoc 1994;30:539.
52. Bradley DM, Scardino MS, Swaim SF. Construction of a weight-bearing surface on a dog distal pelvic limb. J Am Anim Hosp Assoc 1998;34:387.
     

Introduction

Skin grafting in dogs and cats is most commonly used for reconstructing degloving injuries on the extremities, but can also be used to cover skin defects on other areas of the body when simpler techniques may not be indicated or applicable. The use of both full-thickness and split-thickness grafts has been described but I have almost always used full-thickness grafts. Full-thickness grafts consist of the epidermis and entire dermis, whereas split-thickness grafts consist of the epidermis and variable portions of the dermis (Figure 41-23). Of the various types of skin grafts described in the literature, the mesh skin graft offers many advantages for the veterinary surgeon. A mesh graft is a full-thickness or split-thickness skin graft in which parallel rows of staggered slits have been cut either manually with a No. 11 scalpel blade or mechanically with a commercial mesh dermatome. Mesh grafts have the following advantages: 1) they can be expanded to cover large defects if donor sites are limited (e.g., burns); 2) they conform well to irregular surfaces; 3) the creation of numerous slits allows drainage from underneath the graft; and 4) they can be placed over areas that are difficult to immobilize. The primary disadvantage of mesh grafts is that when they are expanded and the interstices heal by epithelialization, resulting in islands of nonhaired epithelium throughout the graft. For this reason, a nonexpanded or minimally expanded graft is preferred.
 

Preoperative Considerations

Recipient Bed

Skin grafts can be successfully placed on freshly created surgical wounds or on healthy granulation beds. A freshly created wound can be grafted immediately if the surface of the wound has a blood supply sufficient enough to produce granulation tissue if left ungrafted. Muscle and fascia generally support grafts well. Bone, cartilage, and tendon covered by their supporting structures also support grafts. Grafts placed over avascular areas less than 1cm in width (0.5cm from each margin) generally survive because of the extensive interconnection of blood vessels within the dermis; this is referred to as the bridging phenomenon.

Although fresh wounds can be successfully grafted, I prefer to allow a healthy granulation bed to form before grafting. A granulation bed should be sufficiently formed within 5 to 7 days. A healthy granulation bed is smooth and pink; the migration of epithelium from the wound margin is also a good indicator that the granulation tissue is healthy. Chronic granulation tissue is rough and dark red and may be infected. Chronic granulation tissue should be excised to its base and a fresh granulation bed allowed to form before any skin-grafting procedure is performed. Culture and sensitivity testing should be considered if infection is suspected. In most instances, traumatic wounds are best managed conservatively initially, followed by grafting after a healthy granulation bed has formed. Obviously, devitalized tissue should be debrided from the wound, and open wound management performed (e.g. moisture retentive wound dressings, wet-to-dry dressings, vacuum-assisted wound therapy) until a granulation bed forms. Once a granulation bed forms, the wound surface should be protected with nonadherent dressings until grafting is performed.

Donor Sites

Important criteria in selecting a donor site are the color and length of hair with respect to that surrounding the recipient site and also the ability to close the donor site after harvesting the graft. Because abundant skin generally is present on the thorax and neck, large grafts can be harvested from these areas, and primary closure of the donor site is possible.

Split-Thickness Versus Full-Thickness Graft

Split-thickness grafts can be classified as thin (less than 0.008-inch thick), intermediate (0.010 to 0.015-inch thick), or thick (0.015 to 0.025-inch thick), depending on the amount of dermis included. Thin and intermediate-thickness grafts generally do not grow hair well and may have a scaly appearance because of the lack of glandular structures. Thick split-thickness grafts approach full-thickness grafts in depth and therefore grow hair more successfully and result in a more normal appearance than thinner grafts. If thick grafts are harvested, the donor site should be excised and closed primarily, if possible, because healing is usually prolonged, and hair growth may be poor.

Full-thickness grafts have several advantages over split-thickness grafts. Because full-thickness grafts contain all the adnexal components, they are more likely to resemble normal skin than split-thickness grafts. They also generally grow hair well and are able to withstand trauma as well as the surrounding normal skin. In contrast to split-thickness grafts, no specialized equipment is required to harvest full-thickness grafts. Finally, the success rate with full-thickness grafts is at least as good as that obtained with split-thickness grafts. For these various reasons, I recommend using full-thickness grafts unless donor skin is limited (e.g., large burn wounds or multiple degloving injuries). Therefore, the remainder of this chapter describes a practical full-thickness mesh grafting technique that I use almost exclusively when grafting is indicated.

Surgical Technique

The mesh grafting procedure involves four basic steps: 1) preparing the donor and recipient sites; 2) harvesting and preparing the graft; 3) meshing the graft; and 4) applying the graft.

Preparing Donor and Recipient Site

The patient is anesthetized following a standard protocol, and the donor and recipient sites are prepared for aseptic surgery. The donor site should be widely clipped in case a plasty procedure is required for closure. The recipient bed is prepared first, so hemorrhage can be controlled before the graft is applied. Strong antiseptic solution should be avoided, but a dilute solution of chlorhexidine (0.05%) does not affect graft “take” and is used routinely.

Lightly scrape the surface of the granulation bed with a scalpel blade to remove any surface debris and to expose capillary ends. Hold the blade at a 90° angle to the surface to avoid removing too much tissue. At this point, a blood imprint of the recipient site can be made if a full-thickness nonexpanded graft is to be used (see next paragraph). Finally, saline-moistened sponges are applied to the surface of the recipient bed, and digital pressure is used to control hemorrhage. Excessive use of cautery or ligatures should be avoided.

Donor sites for full-thickness grafts usually are abundant. Large grafts can be harvested by the technique described here, and the donor site can be closed primarily. The first step is to make a pattern of the defect if a nonexpanded technique is to be used, especially if the edges of the defect are very irregular. A pattern can be made by obtaining a blood imprint of the recipient site after it is prepared as described previously. After the pattern is made, it is placed on the donor site, with care taken not to reverse the pattern (i.e., turning the pattern over so the dermal side is up and a mirror image of the needed graft is harvested). The pattern should also be placed so the direction of hair growth of the graft matches that of the skin surrounding the wound. An arrow is drawn on the imprint indicating the direction of hair growth on the pattern before removing it from the defect. A skin scribe, sterile new methylene blue, or a scalpel blade can be used to transfer the pattern to the skin before cutting the graft. This is performed so the borders of the pattern can still be followed if the skin is distorted while the graft is being cut.

If the wound edges are fairly regular (e.g., rectangular) or if the graft will be expanded, an exact pattern is not necessary. For nonexpanded grafts, the length and width of the defect are measured at their widest point, and a segment of skin of those dimensions is harvested. Excess skin is trimmed from the edge after the graft is placed on the recipient site. When expanded grafts are needed, the graft should be cut longer in the direction parallel with the mesh incisions to account for the loss of length that occurs as the graft is expanded.

Harvest the graft at the level of the superficial subcutaneous tissue or just deep to the cutaneous trunci muscle if it is present. After the graft is dissected free from the donor site, the subcutaneous tissue (and cutaneous trunci muscle if present) must be removed from the graft. Removal of the subcutaneous tissue is enhanced by suturing the graft, dermal side up, to a piece of sterile cardboard with sutures or hypodermic needles (Figure 41-24). Sharp scissors are then used to cut the subcutaneous tissue from the graft. The base of the hair follicles is visible when the subcutaneous tissue is removed, giving the graft a cobblestone appearance. Because the hair follicles extend into the subcutaneous tissue in part of the hair growth cycle, the hair follicles may be damaged and hair growth reduced. Failure to remove all the subcutaneous tissue impairs revascularization of the graft and is an important cause of graft loss.
 

Meshing the Graft

Meshing can be accomplished with a No. 11 scalpel blade or a mesh dermatome but I typically use a scalpel blade because it is convenient and inexpensive. If a scalpel is used, the graft is left attached to the sterile cardboard, and staggered rows of parallel slits (approximately 0.5 to 1 cm in length) are cut in the graft (Figure 41-25). The degree of expansion achievable is influenced by the number of rows and length of the slits. Increasing the number of rows and the length of the slits increases the amount of expansion possible.
 

Application of the Graft

After the skin graft is harvested and prepared, it is placed on the recipient bed. To avoid disrupting the fibrin seal that begins to form soon after the graft is placed on the recipient bed, the graft should be manipulated as little as possible. The edge of the graft is sutured to the edge of the recipient bed using either nonabsorbable monofilament suture material or surgical staples. Alternatively, the graft is allowed to overlap the surrounding skin several millimeters and sutures are placed between the overlapped graft edge and skin below. The overlapped portion of graft will die and separate from the surviving graft, minimizing the risk of traumatizing the graft during suture removal. I have not noticed a significant difference using either technique but prefer suturing the graft to the skin edges of the recipient wound bed. Tacking sutures may be placed between the graft and graft bed on large grafts to help immobilize the graft.

Postoperative Care

Proper postoperative management is essential to successful skin grafting. Complete immobilization of a graft is necessary until a fibrous union occurs between the graft and recipient bed. Immediately after the surgical procedure, the graft is covered with a nonadherent pad. I apply an antibiotic ointment such as gentamycin ointment to the pad before placing it over the graft. A layer of absorbent material (e.g., Telfa WetPruf pads [Kendall Company Hospital Products] or cast padding is applied next and is covered with elastic gauze. Cast padding is easier to conform to the limb but is not as absorbent. If the graft crosses a joint, a splint is incorporated in the bandage to immobilize the limb. Finally, the entire bandage is covered with cohesive elastic bandage material or elastic tape. The bandage should provide moderate pressure. The dressing usually is changed in 48 hours but can be changed as early as 24 hours if drainage from the recipient bed soaks through the surface of the bandage. Care must be taken not to disturb the graft. Fractious animals should be sedated if necessary.

Because a moderate amount of drainage from the graft bed is common, waiting longer than 48 hours to change the bandage is not recommended. Bandages usually are changed every other day for the first 10 days and then as needed for 2 more weeks. Splinting usually can be discontinued after 10 days if the graft has healed normally. Healing grafts normally pass through a series of color changes during the healing process. Initially, many grafts appear pale because of the lack of blood supply. After 2 to 3 days, a graft normally develops a dark red or bruised appearance as the blood supply is reestablished. The graft may also appear edematous because of venous congestion. Graft areas that remain white or turn black will probably slough. Unless the entire graft is obviously nonviable, questionable areas are left until healing is complete. Attempts to remove small areas of nonviable graft may disrupt healing of surrounding areas. In some instances, partial thickness loss occurs leaving viable dermis in the deeper parts of the graft. The surface re-epithelializes from surrounding viable epidermal cells and from epidermal cells in the hair follicles.

Postoperative infection can have devastating results. Infection between the graft and the recipient bed may result in dissolution of the fibrin seal, or the graft may be physically elevated from the graft bed by the exudate produced. Care must be taken not to contaminate the graft when bandages are changed. Full-thickness skin grafts may develop a superficial infection, especially if revascularization is delayed. This generally is the result of the overgrowth of normal skin flora on abnormal skin and does not affect graft take. Infection usually is controlled by swabbing the graft lightly with an antiseptic solution when the bandages are changed and applying a topical antibiotic ointment. Sutures are removed 10 days postoperatively. The patient’s owner should be cautioned to watch for developing paresthesia, as evidenced by constant licking and chewing at the graft. This problem is not common, but it is distressing if the patient chews off a successful graft. If this problem occurs, the graft should be protected with bandages for a longer period or a collar applied to prevent the animal from being able to traumatize the site.

Suggested Readings

Fowler D: Distal limb and paw injuries. Vet Clin Small Anim 2006; 36: 819-845.

Swaim SF, Henderson RA: Wounds on the limbs. In: Small animal wound management. Philadelphia: Lea & Febiger, 1990.

Macphail CM: Skin grafts. In: Fossum TW (ed). Small animal surgery 4th ed. St. Louis: Mosby-Elsevier, 2013.
 

Reconstructive microsurgery refers to the use of the operating microscope and microvascular technique in facilitating reconstruction of difficult or complex wounds. The premise of reconstructive microsurgery involves harvesting autogenous tissue from a body part distant to the wound, transferring that tissue into the wound bed for reconstruction, and reestablishing the transferred tissue’s blood supply by microvascular anastomosis of vessels feeding the flap to vessels adjacent to the wound bed. Tissues transferred in this manner are most commonly termed “free flaps.” Microvascular tissue transfer, free tissue transfer, and vascularized grafts are terms also used to refer to microsurgically transplanted tissue.

Free flaps are further described according to the tissue or tissues comprising the flap. Cutaneous free flaps refer to flaps incorporating skin and subcutaneous tissue. Free muscle flaps, omental flaps, jejunal flaps, and autogenous vascularized bone grafts are other examples of tissue transfers incorporating a single tissue type. Compound flaps incorporate more than one tissue type and are described accordingly. Myo-cutaneous flaps incorporate both muscle and skin; myo-osseous flaps incorporate muscle and bone; osteomusculocutaneous flaps incorporate bone, muscle, and skin.

Successful application of microvascular tissue transfer was first reported in human patients in the early 1960s. The development of instrumentation, suture, and needles appropriate to the repair of small vessels was a prerequisite. Throughout the 1970s and 1980s, a plethora of manuscripts detailing microvascular flaps and techniques in human patients appeared in the literature. Free tissue transfer is now strongly integrated into orthopedic and reconstructive surgery.

Veterinary reconstructive microsurgery is comparatively in its infancy. However, several microvascular flaps have been described experimentally and have been applied clinically to reconstructive problems in dogs. The purpose of this discussion is to detail the latest developments in veterinary reconstructive microsurgery and to provide the reader with some insight into future potential applications.

Recipient Site Requirements

Tissues used in free flaps vary according to the requirements of the recipient wound. A detailed assessment of the wound bed should be performed to obtain an optimal outcome after reconstruction. One of the greatest advantages of microvascular tissue transfer is the ability to select from various tissues and donor sites to best suit the patient’s specific reconstructive requirements. Timing of reconstruction may also vary according to the status of the wound or exposure of vital structures.

Vascular supply is paramount to successful wound healing. Complex and high-velocity impact wounds are often associated with extensive vascular disruption. Loss of blood supply delays wound healing and increases the incidence of complications, especially in instances of orthopedic injury with associated soft tissue disruption.¹ Adequate debridement of devitalized tissue, followed by vascular enhancement through early reconstruction, is beneficial in these patients. Muscle is most efficacious in the revascularization of ischemic wound beds.^2-6 Free microvascular transfer of muscle into the wound bed assists in neovascularization of the wound and provides a source of systemic factors reducing the incidence of wound sepsis.

Structural requirements of the recipient site must also be considered in selecting appropriate tissues for microvascular transfer. In the simplest of cases, the wound may simply require a volume of tissue to replace a tissue deficit. This may be accomplished using various tissues and flaps. The specific selection of donor site depends, in these instances, on ease of access and volume of tissue required. More complex wounds, such as segmental bone loss, may have specific structural requirements that are the major determining factors in selection of donor tissue.

Functional requirements of the recipient site frequently play a role in determining the optimal donor tissue. For example, little benefit results from reconstructing a wound with loss of a vital functional muscle group unless that function is restored. Functional muscle transfer has not been reported clinically in the dog, but is used in human patients for facial reanimation and restoration of flexor function after forearm trauma.^7,8 The functional requirements of weight-bearing surfaces are particularly problematic after extensive injury to the footpads. Reconstruction using “like tissue” is ideal in such circumstances. Sensory reinnervation, although not of certain necessity, may also be accomplished through the use of a neurovascular free flap that incorporates a sensory nerve as well as a vascular pedicle. Sensory nerve repair of the donor nerve to an appropriate recipient nerve may assist in the ultimate protection of the transferred tissue against ongoing weight-bearing stresses.

Donor Site Selection

Selection of an appropriate donor tissue depends on the requirements of the recipient site. Factors to consider in the specific selection of a donor site include ease of surgical dissection, morbidity associated with loss of the donor tissue, matching of donor tissue to recipient requirements, and the ability to access both donor and recipient sites simultaneously. Free tissue transfer has been described as the art of “robbing Peter to pay Paul.” The surgeon must ensure that Peter does, in fact, have what Paul needs and that, by stealing it, Peter will not suffer undue consequences.

Technical Considerations

Successful free tissue transfer depends on detailed advance planning. Familiarity of the surgical team with the procedure, patient positioning, stability of the patient under anesthesia, and selection and preparation of recipient vessels all may affect outcome.

Angiosomes

An angiosome is defined as a region of tissue or tissues perfused by a single-source artery and vein (Figure 41-26).⁹ Adjacent angiosomes are interconnected by vessels termed choke anastomoses. These communications are of obvious biologic advantage. After vascular injury, an angiosome normally dependent on the injured vessel generally receives adequate vascular supply from adjacent angiosomes. However, anatomic continuity of angiosomes does not necessarily ensure physiologic continuity of vascular supply in the event of vascular injury.

The concept of the angiosome is central to the development of free tissue flaps. Tissue incorporated in a free flap should lie, ideally, entirely within the primary angiosome of the source artery and vein, to ensure survival after revascularization. Demonstration of tissue survival beyond the primary angiosome has been demonstrated with cutaneous axial pattern pedicle flaps and with some pedicled muscle flaps.^10-12 As a general rule, a single, smaller angiosome adjacent to the primary angiosome survives when incorporated into the flap design. Dissection beyond the level of a single secondary angiosome should be considered tenuous and likely to lead to partial flap failure.
 

Anatomic descriptions of many cutaneous and muscle angiosomes have been provided for the dog, with few specific descriptions for the cat.^13-22 Based on this information, as well as on experimental data, several regional angiosomes and free flaps have been described. The importance of understanding the anatomy, consistency, and variability of regional vascular patterns cannot be overstated when undertaking microvascular tissue transfer.

Flap Dissection

The particular approach to flap dissection depends on the tissue harvested. Several guidelines and recommendations are common to dissecting all flaps for microvascular transfer. The tissue to be harvested must be isolated to the level of its source artery and vein. All supporting microvasculature must be preserved during this process. All underlying subcutaneous tissue should be incorporated with cutaneous flap dissections; underlying superficial cutaneous musculature should be incorporated in regions where such musculature exists. For example, the cutaneus trunci muscle should be incorporated with elevation of the thoracodorsal cutaneous flap. Muscle is readily dissected because of surrounding fascial sheaths. A soft tissue envelope is incorporated with dissection of vascularized bone grafts to preserve myoperiosteal vasculature. The reader should consult references pertaining to specific flaps, as well as the first section of this chapter, for details of surgical harvest.

Tissue is generally elevated beginning at a site distant to the vascular pedicle. Flap dissection is then continued until the source artery and vein are identified. Bleeding vessels encountered during this process should be meticulously controlled with bipolar electrocoagulation, suture ligation, or vascular clips. Once the vascular pedicle is identified, the artery and vein are skeletonized. Small branches encountered during vascular dissection may be electrocoagulated or clipped with vascular clips, depending on size. The surgeon must avoid damage to the intima of the parent vessel by excessive traction on small vascular branches or aggressive electrocautery. As much surrounding ad-ventitia as possible should be removed during initial dissection of the vascular pedicle. Surgical loupes providing a magnification of 3x to 4x facilitate identification of fine anatomic detail and atraumatic dissection of the vascular pedicle.

The length of vascular pedicle depends primarily on the anatomy of the donor flap. As a general rule, as much length as possible should be included with the initial vascular dissection. Excess length may be trimmed after transfer to the recipient site. A minimum vascular pedicle length of 1 cm is preferred, to allow manipulation of vessels during microanas-tomosis.

To minimize flap ischemia time, the vascular pedicle should not be ligated and divided before preparation of the recipient site. At that time, the artery and vein are independently ligated with vascular clips and are transected using fine vascular scissors.

Recipient Site Preparation

The recipient site should be free of devitalized tissue or active infection. Judicious debridement and lavage should be used to minimize contamination and necrotic tissue in open wounds. Early reconstruction of open wounds using vascularized tissues minimizes the risk of wound complications. In my experience, most open wounds can be converted to a state suitable for microvascular reconstruction within 48 hours of injury. Minimal debridement should be required at the time of microsurgical reconstruction. The wound bed may be lavaged preoperatively with an antibacterial solution, such as 0.05% chlorhexidine gluconate, to decrease bacterial contamination.

Recipient vessels, appropriate for anastomosis to the artery and vein of the flap to be transferred, must be identified and dissected. A knowledge of regional vascular anatomy is obviously a prerequisite. In patients with severe trauma, or a past history of trauma or surgery involving the affected area, preoperative angiography should be considered to identify variations in vascular anatomy. Recipient vessels should approximate the diameter of donor vessels, assuming end-to-end anastomosis. End-to-side technique is often used for arterial anastomosis, to preserve arterial supply distal to the wound. In this event, the recipient artery should be of larger diameter than the donor artery. Recipient vessels should be dissected beyond the wound’s zone of trauma. The surgical approach used for vascular dissection should involve elevation of a skin flap such that the incision will not directly overlie the vascular anastomosis after skin closure.

The free flap is secured at the recipient site before initiating microvascular anastomosis. In the case of soft tissue flaps, this is accomplished using a few strategically placed simple interrupted sutures. Cutaneous flaps are sutured under minimal tension. Muscle flaps are sutured under sufficient tension to approximate their initial resting length at the donor site. Vascularized bone grafts are stabilized using suitable orthopedic fixation. Microvascular anastomosis of the donor and recipient artery and vein is then completed using an operating microscope and standard microvascular technique. Approximating clamps are not released until the completion of both artery and vein repair.

Pedicle length must be planned to avoid excessive length and redundancy of the pedicle or insufficient length resulting in tension or kinking. The vascular pedicle must be carefully positioned to avoid compression of the anastomosed vessels during closure. The venous pedicle is particularly sensitive to these effects. The vascular pedicle is assessed for patency, and remaining sutures are placed between the flap and the recipient wound bed. Patency should be reassessed before final skin closure. Total operative time is minimized by using two surgical teams. One team harvests the donor tissue while the second simultaneously prepares the recipient site.

Flap Perfusion and Anticoagulation

Uncomplicated free tissue transfer generally requires approximately 4 hours of general anesthesia. More complicated procedures, such as those requiring orthopedic fixation, may necessitate 6 to 10 hours of general anesthesia. Adequate flap perfusion depends on maintaining the cardiovascular stability of the patient during the operative and postoperative periods. Intravenous fluid support during and after surgery is an absolute requirement.

Hypothermia must be controlled to avoid peripheral vasoconstriction and deleterious effects on flap perfusion. Patients are maintained on circulating water blankets, and temperature is monitored both during and after the surgical procedure. A heat lamp may be placed over the flap during the immediate postoperative period, before the patient’s recovery from anesthesia. Bandaging of flaps using a lightly applied, heavily padded bandage protects the flap from trauma and assists in trapping body heat.

No consistent recommendation exists on the use of antithrombotic agents before, during, or after microvascular tissue transfer. The most critical factor in preventing thrombosis of the microvascular anastomosis is appropriate surgical technique, and no amount of antithrombotic therapy can salvage a poorly performed anastomosis. Heparin and saline (10 units heparin per 1 mL saline) are used topically at the anastomotic site to clear the lumen of vessels before anastomosis. Other antithrombotic therapy is determined by the preference of the surgeon and identified patient risk factors.

Aspirin may be used at a dose of 5 to 10 mg/kg body weight preoperatively, to inhibit platelet aggregation.²³ I routinely administer dextran 40 at a dose of 10 mL/kg body weight intraoperatively. Dextran administration expands the vascular space, thereby improving flap perfusion, and it may have an inhibitory effect on platelet function.²⁴ Anticoagulation using systemic heparin is rarely indicated.

Tolerated flap ischemia times vary according to the tissue transferred.^25-27 Skin is considered resistant to the detrimental effects of ischemia and reperfusion. Cutaneous free flaps tolerate 6 to 8 hours of warm (room temperature) ischemia before the onset of significant injury. Muscle is sensitive to ischemia and reperfusion and may demonstrate detrimental effects after 2 to 4 hours of warm ischemia. Total ischemia times in clinical free tissue transfer rarely exceed these time frames. In my experience, flap ischemia times have varied from 60 to 180 minutes.

Occasionally, a flap fails to perfuse after an apparently successful microvascular anastomosis. This is termed a “no-reflow” phenomenon and may be attributed to many causes. In this event, the vascular pedicle extending from the anastomotic site to the flap should be inspected under the operating microscope. Active bleeding through any previously unidentified branches from the pedicle is controlled with vascular clips. Specific attention is paid to areas of potential vascular injury and vasospasm. If a region of vasospasm is identified, 2% lidocaine is placed topically on the vessel. If focal vasospasm persists, then damage to the vessel may be assumed, and microvascular anastomosis should be repeated distal to this site. No reflow may occasionally be caused by inappropriate or traumatic dissection of the flap, with subsequent injury to the supportive microvasculature. This problem is easily avoided through meticulous attention to flap dissection. Little can be done to rectify the situation after its occurrence. Extended ischemia time may lead to reperfusion injury and subsequent occlusion of venous microvasculature by neutrophil adhesion. Therapy aimed at alleviating ischemia-reperfusion injury is indicated, but it is of questionable benefit after the period of reperfusion.

Postoperative Monitoring

Free flaps entirely depend on the integrity of the microvascular anastomsoses. Free flap failure may be caused by venous or arterial thrombosis, either of which must be recognized early and investigated aggressively if the flap is to be salvaged. Venous failure of cutaneous flaps is most easily recognized by the onset of congestion in the flap (Figure 41-27). A purplish-blue discoloration is noted. Bandaged flaps may be assessed by creating a window in the bandage to allow visualization of a portion of the flap. Flaps tolerate venous outflow occlusion poorly. At the earliest indication of this problem, the patient should be returned to the operating room, and the vascular pedicle should be dissected using the operating microscope. Careful attention is paid during the approach to look for evidence of vessel compression or kinking caused by positioning of the vascular pedicle or restrictive skin closure. If this is the case, the anastomosis may actually be patent, and the problem is addressed by simple repositioning of the pedicle or release of the overlying skin incision. In the event of a thrombosed anastomosis, the region of thrombosis is excised, and venous effluent from the flap is documented. Once flow through the flap is established, venous anastomosis is repeated. Sluggish venous outflow may also be treated by application of medicinal leeches. Leeches reduce flap congestion by direct ingestion of blood and by promoting continued hemorrhage from bite wounds resulting from local infusion of hirudin.²⁸
 

Arterial failure can be more difficult to diagnose because it is not associated initially with overt color change of the flap. Flap temperature can be monitored; a drop in temperature indicates arterial insufficiency. This method is unreliable in bandaged flaps, because the bandage traps body heat and artificially elevates flap temperature. Doppler flow probes may be used to monitor arterial patency more reliably in the postoperative period. A window is created in the bandage overlying the arterial pedicle distal to the anastomosis. A pencil Doppler probe is then easily inserted through the window to monitor arterial patency. Bleeding may be a useful indicator of flap perfusion. Cutaneous flaps are punctured with a 20- or 22-gauge hypodermic needle and are monitored for active bleeding from the site. More specialized monitoring techniques such as laser Doppler flowmetry or fluorescein clearance have been described, but they are usually beyond the realm of clinical necessity. 

Monitoring of flaps that do not incorporate a cutaneous component is more difficult. Doppler techniques are useful for monitoring arterial adequacy in such flaps. Venous monitoring is difficult or impossible. Vascularized bone grafts should be assessed using [^99m] technetium scintigraphy within 5 days of operation.

Free Flaps in the Dog and Cat

Several free flaps have been described experimentally, clinically, or both in the dog and cat. Other flaps have been described as pedicled flaps, maintaining a vascular attachment to the donor site. These flaps may be used reliably for free transfer as well, assuming adequate dimensions of the vascular pedicle. Vessel diameters for most described flaps in the dog approximate 1 to 2 mm. Vessel diameters of less than 0.5 mm are associated with increased rates of anastomotic thrombosis.

Cutaneous Flaps

Cutaneous angiosomes have been described extensively, and anatomic landmarks for dissection of pedicled cutaneous axial pattern flaps are well documented. Axial pattern skin flaps may be used for free transfer as well.

The superficial cervical axial pattern flap, based on the direct cutaneous pedicle of the prescapular branch of the superficial cervical artery and vein, has been documented as a free flap in a series of cases (Figure 41-28).^29,30 The vascular pedicle perforates the septum formed by the omotransversarius, cleidocervicalis, and trapezius muscles. The cutaneous angiosome extends dorsally from the point of origin to the midline and roughly incorporates the caudal two-thirds of the cervical skin in a cranio-caudal direction. The amount of skin harvested for transfer is determined, first, by the requirements of the recipient site and, second, by the ability to close the donor site primarily.
 

I have also used the caudal superficial epigastric axial pattern flap sporadically for microvascular transfer. The primary advantage of selecting an axial pattern skin flap for microvascular transfer is ease of dissection. Disadvantages include excessive bulk from inclusion of associated subcutaneous tissue and poor cosmetic result caused by differential hair growth characteristics between donor and recipient sites.

The saphenous fasciocutaneous free flap has been documented in experimental and clinical cases.^28,31 The flap is based on the medial saphenous artery and vein and includes the skin overlying the medial aspect of the thigh (Figure 41-29). Flap dissection includes the superficial fascia of the medial gastrocnemius muscle, giving the flap its designation as fasciocutaneous. Numerous small direct cutaneous vessels arise from the saphenous vessels as they course through the flap. The saphenous fasciocutaneous flap has the advantage of less bulk and improved cosmetic results compared with other free axial pattern skin flaps. The width of the flap is limited by the ability to close the donor site primarily.
 

Muscle Flaps

Muscle probably has the greatest utility of any tissue used for microsurgical reconstruction. Muscle flaps are, for the most part, easily dissected. Most muscles may be harvested with minimal donor site morbidity because of the function of synergic muscle groups. Neovascularization of compromised wound beds is facilitated to a greater degree by muscle than by other tissues. Finally, donor muscles may be selected that closely match the dimensional and functional requirements of nearly any wound reconstruction.

The angiosomes of muscles may be classified into one of five types (Figure 41-30). Type I muscles have a single dominant vascular pedicle. Type II muscles have a single dominant pedicle and one or more minor pedicles. Type III muscles contain two dominant vascular pedicles, each of which has an approximately equal contribution to the muscle’s blood supply. Type IV muscles have a segmental blood supply formed by numerous small pedicles of approximately equal contribution. Type V muscles have a single dominant vascular pedicle near their insertion and a segmental system near the origin of the muscle. Based on assumptions of physiologic blood supply through angiosomes, one can surmise that any type I muscle will survive entirely after free transfer based on the single dominant pedicle. Most type II muscles willl survive based on the dominant pedicle, depending on the number and relative contribution of the minor pedicles. Type III muscles are expected to survive after free transfer based on either dominant pedicle system. Type V muscles generally will survive based only on the single dominant pedicle. Type IV muscles are generally poor candidates for microvascular transfer because of the large number and small contribution of each pedicle system to the muscle’s blood supply. Detailed descriptions of the vascular supply to muscles of the dog have been published.^21,22 The foregoing assumptions given serve as guidelines only. The ultimate reliability of any muscle in reconstructive microsurgery is proved only through experimental or clinical trials that establish its utility. If at all possible, muscle transfers should be limited to single angiosomes or previously documented free flaps.
 

Trapezius Muscle Flap

The vascular supply of the cervical portion of the trapezius muscle has been thoroughly described, as has the entire angiosome of the prescapular branch of the superficial cervical artery and vein (Figure 41-31).³² The cervical portion of the trapezius muscle has a type II vascular supply, with the prescapular branch of the superficial cervical artery forming the dominant pedicle. Experimentally and clinically, survival of the entire cervical portion of the muscle has been consistently documented based solely on this dominant pedicle.

Dissection of the trapezius muscle flap is through a curvilinear incision beginning approximately 2 to 3 cm cranial to the point of the shoulder, extending dorsally parallel to the scapular spine and curving cranially below the dorsal midline.³³ Skin and subcutaneous tissue are dissected from the superficial fascia of the muscle, with care taken to identify and ligate the direct cutaneous branch as it exits the septum formed by the trapezius, omotransversarius, and cleidocervicalis muscles. The cervical portion of the trapezius muscle is sharply incised from its attachment to the scapular spine. Fascial attachments dorsally are incised, and the muscle is elevated carefully. Several muscle branches extending into deep musculature of the neck are identified and are ligated with vascular clips. At this point, the vascular pedicle should be located. The location of the pedicle is variable as it courses deep to the trapezius muscle. It is most commonly located immediately beneath the cranial border of the muscle coursing from ventral to dorsal. In a few instances, the vascular pedicle lies immediately cranial to the cranial border of the trapezius muscle and gives off several smaller muscular branches to the muscle as it extends dorsally. Dissection in these patients must be performed with caution, to preserve the integrity of the vascular pedicle. After identification of the prescapular branch of the superficial cervical artery and vein, remaining muscle attachments are dissected. One or two small muscular branches to the omotransversarius muscle are identified and clipped, and the artery and vein are skeletonized and dissected for a length of at least 2 to 3 cm. The prescapular lymph node is intimately associated with the vascular pedicle and may either be included with the pedicle or carefully excised.

I used the trapezius muscle free flap for distal extremity reconstruction in a series of 20 cases. The trapezius muscle is broad and flat, lending itself well to conformation to many wound beds. Bulk of the flap is minimal and decreases dramatically over the course of several weeks because of denervation atrophy. Despite denervation atrophy, transferred muscle maintains a constant vascular density beneficial to the wound bed. The trapezius muscle is resurfaced using a full-thickness skin graft harvested from a donor site with hair growth characteristics similar to those of the recipient site. This technique has resulted in improved cosmetic results, compared with cutaneous or musculocutaneous free flaps (Figure 41-32). Seroma formation at the donor site is common and should be managed with drain placement for 5 to 7 days.
 

Latissimus Dorsi Muscle Flap

The latissimus dorsi muscle has, historically, been the workhorse for microsurgical reconstruction of complex distal extremity wounds in human patients. Pedicled latissimus dorsi muscle flaps have been used for chest wall reconstruction and experimental cardiomyoplasty in the dog and have been described experimentally for microsurgical transfer in the cat.³⁴ The latissimus dorsi muscle reliably survives in its entirety based solely on the dominant thoracodorsal artery and vein, which enter the deep surface of the muscle near its insertion (Figure 41-33). The muscle is approached through a curvilinear skin incision beginning at the axilla and extending dorsally and caudally to the level of the muscle’s origin. Skin and subcutaneous tissues are dissected from the superficial muscle fascia, with care taken to identify and ligate the direct cutaneous branch of the vascular pedicle, located near the caudal shoulder depression. The origin of the latissimus muscle is identified and is sharply incised. Muscle elevation reveals numerous small muscular branches ex tending from the intercostal arteries. Segmental pedicles are cauterized or ligated and are transected as they are encountered. Dissection continues toward the muscle’s insertion, and the dominant thoracodorsal artery and vein are identified on the deep surface of the muscle. After identification of the vascular pedicle, the muscle’s tendon of insertion is transected, and the thoracodorsal artery and vein are skeletonized for a length of at least 2 to 3 cm. The cat occasionally has a minor pedicle originating from the lateral thoracic artery and vein, which enter the deep surface of the muscle ventrally near its tendon of insertion. This pedicle must be identified and ligated. The thoracodorsal pedicle in the cat has a diameter of approximately 0.4 mm, making microvascular anastomosis difficult. Dissection in the cat is therefore continued to the level of the origin of the subscapular artery and vein from the axillary vessels to facilitate subsequent anastomosis.
 

The dimensions of the latissimus dorsi muscle exceed the requirements of most wound beds in the dog. Its clinical use therefore has been sporadic. The latissimus dorsi muscle is useful as a free flap in patients with massive soft tissue loss secondary to trauma or ablative cancer surgery. I have used the latissimus dorsi free flap for cranial reconstruction after partial craniectomy and orbitectomy for a sebaceous adenocarcinoma in a dog and for reconstruction of a massive rear limb degloving injury with associated orthopedic trauma. Clinical experience with this flap, however, is limited.

Vascularized Bone Grafts

The veterinary literature has no clinical reports, and few experimental descriptions, of autogenous vascularized bone grafts. Numerous reports of vascularized canine bone grafts appear as experimental models in the human literature. The indications, contraindications, and clinical utility of nonvascularized cortical bone grafts are well established. Nonvascularized cortical bone grafts provide immediate structural support in orthopedic reconstruction. Ultimate success depends on revascularization of the cortical graft from the wound bed, followed by gradual resorption and new bone deposition. This process requires years to complete and depends on a favorable wound environment. Osteomyelitis, structural weakening of the graft, and delayed healing of graft-bone interfaces are common complications.

Autogenous vascularized bone grafts are advantageous in that they maintain a vascular supply and, therefore, viability of cellular elements within the graft. Graft bone actively contributes to bone healing and remodeling. Vascularized grafts are more resistant to infection than nonvascularized grafts, lending themselves to the reconstruction of large segmental defects or vascularly compromised wound beds. Vascularized bone grafts described in the dog include rib, fibula, proximal ulna, and distal ulna.³⁵

Vascularized Fibula Graft

The canine fibula graft has been used as an experimental model for the study of vascularized bone graft biology (Figure 41-34).³⁶ The popliteal artery branches into a larger cranial tibial and a smaller caudal tibial artery. The caudal tibial artery enters the interosseous space between the fibula and tibia and is intimately associated with the flexor hallucis longus muscle. The nutrient artery of the fibula arises from the caudal tibial artery and enters the fibula medially in its central third. Dissection of the fibula is performed to maintain a surrounding muscle cuff. Particular care is taken to preserve the flexor hallucis longus muscle with the graft. Subperiosteal dissection of the tibia is required to preserve vasculature within the interosseous space. The fibula may be transferred based either on the caudal tibial artery or on the popliteal artery. Dissection to the level of the popliteal artery necessitates ligation and transection of the cranial tibial artery. Use of the caudal tibial artery as a pedicle may be limited by the diameter of these vessels. Iatrogenic damage to the peroneal nerve must be avoided during proximal dissection of the graft and vascular pedicle. The vascularized fibula graft has not been used clinically in the dog and likely has limited utility for segmental long bone reconstruction because of its poor structural integrity.
 

Vascularized Rib Graft

Microsurgical transfer of the rib has been used in the dog as an experimental model for bone transfer.³⁷ Either the dorsal or the ventral part of the intercostal vascular system may be used as a vascular pedicle for rib transfer. Inclusion of the nutrient artery with the transfer mandates dorsal dissection. 

Ventrally dissected grafts survive based on an intact musculoperios-teal vascular supply. The dorsal intercostal arteries arise from the thoracic aorta. Immediately before entering the intercostal space, a dorsal branch supplying the spinal cord and epaxial muscles is given off. The nutrient artery branches from the dorsal intercostal artery just distal to the tubercle of the rib and extends dorsally to enter the nutrient foramen. The dorsal intercostal artery continues distally in the costal groove on the caudal aspect of the rib, giving off numerous periosteal branches. A lateral cutaneous branch is formed from the dorsal intercostal artery before its anastomosis with the ventral intercostal artery. Intercostal veins parallel the arterial supply, with eventual drainage into the azygous vein. Clinical utility of the rib graft likely will be limited by its curvature and weak structural characteristics. Vascularized rib grafts may prove to have some usefulness in mandibular reconstruction, although this remains to be documented.

Vascularized Proximal Ulna Graft

The canine ulna may be harvested with little resulting functional impairment to limb use. This fact, along with the obvious structural integrity of the ulna, makes it a logical choice for segmental long bone reconstruction. The proximal ulna bone graft is harvested based on the common interosseous vascular pedicle.³⁸ The common interosseous artery arises from the median artery at the level of the proximal radius, immediately enters the interosseous space from the medial side, and bifurcates into caudal and cranial interosseous branches. The caudal interosseous artery continues distally in the interosseous space, where it gives rise to the nutrient arteries of the radius and ulna, as well as to multiple periosteal branches. The nutrient artery of the ulna enters near the junction of the proximal and central thirds of the bone. The cranial interosseous artery emerges from the interosseous space laterally, where it gives rise to muscular branches to the extensor carpi ulnaris and the lateral and common digital extensor muscles.

Dissection of the proximal ulna graft is performed through a curvilinear caudolateral skin incision. Fasciotomy of the flexor and extensor muscle groups facilitates muscle dissection and identification of vascular structures. Separation between the extensor carpi ulnaris and the lateral digital extensor muscles proximally reveals vascular branches to these muscles. These muscular branches serve as a consistent landmark indicating the level of the vascular pedicle of the flap (Figure 41-35). The lateral radial periosteum is incised along the cranial surface of the abductor pollicis longus muscle, and subperiosteal dissection of the radius is continued into the interosseous space. The medial radial periosteum is similarly incised and elevated. Distal osteotomy of the ulna is then performed using an oscillating bone saw. The caudal interosseous artery and vein are identified within the interosseous space, ligated, and divided. Proximal osteotomy of the ulna is performed proximal to the level of the vascular pedicle. Circumferential subperiosteal dissection of the ulna is performed at this level, and the ulna is osteotomized. Muscular branches to the extensor muscles are ligated and divided. Cautious elevation of the os-teotomized ulna reveals the common interosseous pedicle on the medial aspect of the graft. The common interosseous artery and vein are dissected to their point of origin from the median artery and vein.
 

Advantages of the proximal ulna graft include structural integrity and provision of a nutrient blood supply. Primary disadvantages include the necessity of proximal osteotomy adjacent to the elbow joint, difficult dissection of the vascular pedicle because of its medial location, and limited length of the vascular pedicle. The proximal ulna graft has been documented experimentally, but it has not yet been used clinically in the dog.

Vascularized Distal Ulna Graft

The distal ulna graft has great potential for clinical use in the dog.³⁹ The approach to initial dissection of the graft is identical to that described for the proximal ulna graft. After fasciotomy of the flexor and extensor muscle groups, the caudal interosseous artery and vein are identified as they exit the interosseous space caudomedially at the level of the distal ulna. These vessels are ligated and transected. The ulna is circumferentially dissected immediately distal to this level and is osteotomized using an oscillating bone saw. Dissection of the medial and lateral radial periosteum is performed as described for the proximal ulna transfer and is continued proximally. Subperiosteal dissection of the radius must be performed with great caution to avoid damage to the caudal interosseous vessels as they course through the interosseous space. The length of graft required for recipient site reconstruction is calculated. Proximal osteotomy is performed after circumferential subperiosteal dissection of the ulna. The proximal osteotomy should be performed such that the resulting length of bone graft is 2 to 3 cm longer than that required for the reconstructive procedure (Figure 41-36). The caudal interosseous artery and vein are located within the interosseous space, ligated with vascular clips, and transected. Once harvested, the interosseous artery and vein are dissected for a length of approximately 3 cm. The bone graft is then shortened to its required length by osteotomizing that portion of proximal ulna from which the vascular pedicle has been dissected.

The distal ulna graft depends entirely on an intact musculoperiosteal circulation for survival. An intact musculoperiosteal cuff must be included with the dissection, to include the ulnar head of the deep digital flexor, the pronator quadratus, and the abductor pollicis longus muscles. External skeletal fixation is recommended to minimize implant-associated embarrassment of the periosteal vasculature.

The utility of the vascularized distal ulna graft has been demonstrated experimentally.⁴⁰ I have used the distal ulna graft for reconstruction of the distal radius after limb-sparing surgery for osteosarcoma and for reconstruction of a mandibular nonunion and segmental defect caused by a gunshot injury.
 

Compound Flaps

Compound free flaps incorporate tissues of more than one type. They may be useful for the reconstruction of complex trauma involving loss of multiple tissue types. A detailed knowledge of vascular anatomy allows the surgeon the flexibility of designing many compound flaps.

Musculocutaneous flaps combine both muscle and skin in the transfer. The superficial cervical axial pattern skin flap may easily be included with the cervical portion of the trapezius muscle by maintaining the direct cutaneous branch rather than by ligating it during dissection. The vascular supply to both muscle and skin is based on the prescapular branch of the superficial cervical artery and vein. Similarly, the thoracodorsal axial pattern skin flap may be incorporated with the latissimus dorsi muscle flap. Dissection of musculocutaneous free flaps must be carefully planned to include appropriate dimensions of the cutaneous component. With inclusion of an axial pattern skin flap, the cutaneous component may be used to overlie the transferred muscle directly and to reconstruct an associated cutaneous defect. The axial pattern skin flap may also be dissected free of the muscle flap, with care taken to maintain the direct cutaneous artery and vein. This allows use of both the muscle and cutaneous components for reconstruction of adjacent portions of large wound beds (Figure 41-37).
 

Myo-osseous flaps incorporate both muscle and bone. By strict definition, all vascularized bone grafts may be considered myo-osseous because of the preservation of an intact musculoperiosteal cuff. However, the term is recognized to designate the inclusion of a significant muscle component used in the reconstruction. The successful inclusion of the scapular spine with the cervical trapezius muscle flap has been demonstrated experimentally (Figure 41-38).⁴¹ Survival of the scapular spine depends on its periosteal vascular supply. Unfortunately, the scapular spine lies outside the primary angiosome of the prescapular branch of the superficial cervical artery, and this causes some concern relative to the reliability of its vascular integrity after transfer. I have used the cervical trapezius myo-osseous flap for reconstruction of metatarsal segmental defects and overlying soft tissue loss caused by a gunshot injury in a Chesapeake Bay retriever. Survival of the muscle flap and its overlying free skin graft was evident. However, postoperative [^99m]technetium scintigraphy of the bone graft was negative. This bone graft proceeded to rapid incorporation and healing, a finding suggesting either an intact vascular supply or rapid revascularization. Based on the negative scintigraphy results in this dog and the tenuous vascular integrity of the flap design, the cervical trapezius myo-osseous flap should be used with caution.
 

The vascularized rib graft may be harvested as an osteocutaneous flap by preserving the cutaneous branch of the dorsal intercostal artery and its associated skin paddle. Maintenance of the skin paddle facilitates postoperative monitoring of vascular integrity of the flap. This flap may also be of benefit in mandibular reconstruction with associated skin loss.

Reconstruction of Weight-Bearing Surfaces

Reconstruction of weight-bearing surfaces poses a particular problem because of the stresses placed on the repair. Tissue used for such reconstruction must be durable and resilient. Local footpad transposition techniques and free pad grafts have been described for footpad reconstruction.^42-45 Marginal recipient beds may compromise the success of free grafts, and extensive trauma may preclude local transposition techniques. Free vascularized transfer of footpads may be used for reconstruction in such cases.

A microvascular transfer of the fifth digital footpad was described previously (Figure 41-39).⁴⁶ This procedure involves a digital fillet of the fifth rear digit. All phalangeal bones are dissected extraperiosteally and are excised through a dorsal skin incision. The digital pad and surrounding skin are then harvested, based on the deep plantar metatarsal artery IV and the superficial dorsal metatarsal vein IV. Sensory innervation is provided by the deep plantar metatarsal nerve IV and parallels the arterial supply to the footpad. Transfer may be accomplished as a microvascular free flap or as a neuromicrovascular free flap with repair of the donor nerve to a sensory nerve branch at the recipient site. The absolute necessity of sensory reinnervation in such flaps is not established.
 

The carpal pad may also be transferred as a microvascular free flap. This flap is advantageous in that a larger area of surrounding skin may be included with the flap, and harvest does not necessitate digital amputation. The smaller size and conical shape of the carpal pad make initial resurfacing of the weight-bearing surface more difficult compared with the digital pad flap. The carpal pad flap is dissected based on the caudal interosseous artery as it courses through the carpal tunnel. Two to three small venous branches from the medial aspect of the flap drain into the cephalic vein, which serves as the venous pedicle.

Both the digital pad flap and the carpal pad flap have been used for reconstruction of severely traumatized feet in dogs. The transferred pads have proved resilient to weight-bearing stresses and have undergone hypertrophic change in response to continued weight bearing. Precise positioning of the pad is essential to avoid trauma to surrounding hirsute skin. The most common complication of microvascular footpad transfer has been chronic incisional breakdown at the junction of donor and recipient skin caused by repeated tensile stresses placed on the wound. Functional reconstruction of weight-bearing surfaces is difficult. Further research and experience are needed before firm recommendations can be made regarding optimal techniques.

Complications of Free Flaps

Complications associated with microvascular tissue transfer may be divided into recipient site and donor site problems. Donor site complications are site specific, depending on the tissue harvested. Difficulties arising from loss of the donor tissue should not be seen if appropriate consideration has been given to selection of a donor site. Seroma formation is common after harvest of soft tissue flaps, particularly muscle flaps. The large amount of dead space and inherent movement between tissue planes in these instances makes prevention of seromas difficult. Tacking or walking sutures are not recommended for dead space management after dissection of muscle flaps because they restrict movement and increase postoperative discomfort. Dead space is managed by provision of surgical drainage; drainage for 5 to 7 days is adequate in most instances.

Cross-contamination from the recipient site to the donor site may result in donor site infection. Care should be taken to use separate instrumentation in each surgical field. The surgical team responsible for dissection of the donor site should avoid contact with the recipient site, and vice versa.

Recipient site complications may be caused by inappropriate preparation of the recipient wound bed or by flap-related complications. Microsurgically transferred flaps are excellent sources of vascularized tissue for reconstruction, but they should not be viewed as a panacea for a poorly prepared wound bed. Necrotic tissue and debris must be surgically removed from the wound before transfer. In the case of osteomyelitis, infected bone must be thoroughly debrided. Free flaps should not be placed onto heavily contaminated or overtly infected wound beds. Such wounds should be aggressively converted to a clean contaminated state and subsequently reconstructed.

Flap-related complications may be specific to the tissue transferred, such as loss of orthopedic fixation in vascularized bone grafts or incisional dehiscence of transferred footpads. Complications common to all flaps relate to the integrity of the microvascular anastomosis. Meticulous attention to anastomotic technique, astute postoperative monitoring and early surgical re-exploration of compromised flaps are mandatory.

The relative advantages and disadvantages of microsurgical reconstruction are well documented in the human literature. Our understanding of the potential of these techniques in veterinary surgery is expanding. Successful use of microsurgical tissue transfer requires appropriate instrumentation and a familiarity with microvascular technique, both of which are increasingly available at larger veterinary referral centers. Further experience with, and definition of, these techniques will inevitably lead to increased veterinary clinical application.

References

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3. Richards RR, Schemitsch EH. Effect of muscle flap coverage on bone blood flow following devascularization of a segment of tibia: an experimental investigation in the dog. J Orthop Res 1989;7:550-558.
4. Richards RR, McKee MD, Paitich B, et al. A comparison of the effects of skin coverage and muscle flap coverage on the early strength of union at the site of osteotomy after devascularization of a segment of canine tibia. J Bone Joint Surg Am 1991; 73:1323-1330.
5. Anthony JP, Mathes SJ, Alpert BS. The muscle flap in the treatment of chronic lower extremity osteomyelitis: results in patients over 5 years after treatment. Plast Reconst Surg 1991; 88:311-318.
6. Jaeger K, Stark GB. Clinical and experimental evidence for the improvement of perfusion from free myocutaneous flaps. In: Stuttgart DR, ed. Microsurgical tissue transplantation. Chicago: Quintessence, 1989:217-222.
7. McKee NH, Kuzon WM. Functioning free muscle transplantation: making it work? What is known? Ann Plast Surg 1989; 23:249-254.
8. Manktelow RT, Zuker RN. The principles of functioning muscle transplantation: applications to the upper arm. Ann Plast Surg 1989;22:275-281.
9. Taylor GI, Minabe T. The angiosomes of the mammals and other vertebrates. Plast Reconst Surg 1992;89:181-215.
10. Gregory CR, Gourley IM, Koblik PD, et al. Experimental definition of latissimus dorsi, gracilis, and rectus abdominis musculocutaneous flaps in the dog. Am J Vet Res 1988;49:878-884.
11. Weinstein MJ, Pavletic MM, Boudrieau RJ. Caudal sartorius muscle flap in the dog. Vet Surg 1988,17:203-210.
12. Solano M, Purinton PT, Chambers JN, et al. Effects of vascular pedicle ligation on blood flow in canine semitendinosus muscle. Am J Vet Res 1995;56:731-735.
13. Pavletic MM. Canine axial pattern flaps, using the omocervical, thoracodorsal, and deep circumflex iliac direct cutaneous arteries. Am J Vet Res 1981;42:391-406.
14. Pavletic MM. Caudal superficial epigastric arterial pedicle grafts in the dog. Vet Surg 1980;9:103-107.
15. Henney LHS, Pavletic MM. Axial pattern flap based on the superficial brachial artery in the dog. Vet Surg 1988; 17:311-317.
16. Smith MM, Shults S, Waldron DR, et al. Platysma myocutaneous flap for head and neck reconstruction in cats. Head Neck 1993;15:433-439.
17. Smith MM, Payne JT, Moon ML, et al. Axial pattern flap based on the caudal auricular artery in dogs. Am J Vet Res 1991; 52:922-925.
18. RemediosAM,BauerMS,BowenCV.Thoracodorsal and caudal superficial epigastric axial pattern skin flaps in cats. Vet Surg 1989;18:380-385.
19. Weinstein MJ, Pavletic MM, Boudrieau RJ, et al. Cranial sartorius muscle flap in the dog. Vet Surg 1989,18:286-291.
20. Degner DA, Bauer MS, Steyn PF, et al. The cranial rectus abdominis muscle pedicle flap in the dog. Vet Comparative Orthop Traumatol 1994;7:21-24.
21. Purinton PT, Chambers JN, Moore JL. Identification and categorization of the vascular patterns to muscles of the thoracic limb, thorax, and neck of dogs. Am J Vet Res 1992;53:1435-1445.
22. Chambers JN, Purinton PT, Allen SW, et al. Identification and anatomic categorization of the vascular patterns to the pelvic limb muscles of dogs. Am J Vet Res 1990;51:305-313.
23. Jackson M. Platelet physiology and platelet function: inhibition by aspirin. Compend Contin Educ Pract Vet 1987;9:627-638.
24. Concannon KT, Haskins SC, Feldman BF. Hemostatic defects associated with two infusion rates of dextran 70 in dogs. Am J Vet Res 1992;53:1369-1372.
25. Zelt RG, Olding M, Kerrigan CL, et al. Primary and secondary critical ischemia times of myocutaneous flaps. Plast Reconstr Surg 1986;78:500-503.
26. Picard-Ami LA, Thomson JG, Kerrigan CL. Critical ischemia times and survival patterns of experimental pig flaps. Plast Reconstr Surg 1990;86:739-743.
27. Kerrigan CL, Zelt RG, Daniel RK. Secondary critical ischemia time of experimental skin flaps. Plast Reconstr Surg 1984; 74:522-526.
28. Degner DA, Walshaw R. Medial saphenous fasciocutaneous and myocutaneous free flap transfer in eight dogs. Vet Surg 1997; 26:20-25.
29. Fowler JD, Miller CW Bowen V, et al. Transfer of free vascular cutaneous flaps by microvascular anastomosis: results in six dogs. Vet Surg 1987;16:446-450.
30. Miller CW, Fowler JD, Bowen CVA, et al. Experimental and clinical free cutaneous transfers in the dog. Microsurgery 1991;12:113-118.
31. Degner DA, Walshaw R, Lanz O, et al. The medial saphenous fasciocutaneous free flap in dogs. Vet Surg 1996;25:105-113.
32. Philibert D, Fowler JD, Clapson JB. The anatomic basis for a trapezius muscle flaps in dogs. Vet Surg 1992;21:429-434.
33. Philibert D, Fowler JD, Clapson JB. Free microvascular transfer of the trapezius musculocutaneous flap in dog. Vet Surg 1992;21:435-440.
34. Nicoll SA, Fowler JD, Remedios AR, et al. Development of a free latissimus dorsi muscle flap in cats. Vet Surg 1996;22:40-48.
35. Fowler JD, Levitt L, Bowen CVA. Microsurgical free bone transfer in the dog. Microsurgery 1991;12:145-150.
36. Brown K, Marie P, Lyszakowski T, et al. Epiphysial growth after free fibular transfer with and without microvascular anastomosis. J Bone Joint Surg Br 1983;65:493-501.
37. Ostrup LT, Fredrickson JM. Distant transfer of a free, living bone graft by microvascular anastomoses. Plast Reconstr Surg 1974;54:274-285.
38. Levitt L, Fowler JD, Longley M, et al. A developmental model for free vascularized bone transfers in the dog. Vet Surg 1988;17:194-202.
39. Szentimrey DG, Fowler JD. The anatomic basis of a free vascularized bone graft based on the distal canine ulna. Vet Surg 1994;23:529-533.
40. Szentimrey DG, Fowler JD, Johnston C, et al. Transplantation of the canine distal ulna as a free vascularized bone graft. Vet Surg 1995;24:215-225.
41. Philibert D, Fowler JD. The trapezius osteomusculocutaneous flaps in dogs. Vet Surg 1993;22:444-450.
42. Swaim SF, Bradley DM, Steiss JE, et al. Free segmental paw pad grafts in dogs. Am J Vet Res 1993;54:2161-2170.
43. Swaim SF, Riddell KP, Powers RD. Healing of segmental grafts of digital pad skin in dogs. Am J Vet Res 1992;53:406-410.
44. Gourley IM. Neurovascular island flap for treatment of trophic metacarpal pad ulcer in the dog. J Am Anim Hosp Assoc 1978;14:119-125.
45. Basher A. Foot injuries in dogs and cats. Compend Contin Ed Pract Vet 1994;16:1159-1176.
46. Basher AWP, Fowler JD, Bowen CV, et al. Microneurovascular free digital pad transfer in the dog. Vet Surg 1990;19:226-231.
     

Indications

The paws of a dog and cat play a significant role in their ambulatory abilities; thus, when an animal has paw skin defects, some form of reconstruction or salvage surgery is necessary to preserve normal ambulation. Minor paw defects may only require a simple reconstructive surgical technique, such as suture of a pad laceration. Conversely, major defects may require a more involved reconstruction or salvage surgical technique as with a skin graft to reconstruct a massive skin defect. With severe paw trauma, limb amputation is often performed, whereas if paw salvage techniques are available, limb amputation may possibly be avoided. In other instances of severe paw trauma, limb amputation is not an option, and reconstruction or salvage becomes necessary, as in the instance of a cat with bilateral avascular necrosis of the forepaws caused by excessively tight bandages following onychectomy. In the working dog and canine athlete, in which limb and paw functions are essential for performance, strong functional reconstruction and salvage procedures are especially important.

Defects of the paws can involve the dorsal surface, palmar or plantar surface (pads), interdigital surfaces, or interpad surfaces. Certain larger wounds on the dorsum of the paw and distal limb can be managed by techniques such as skin grafts and flaps, which are described in earlier sections of this chapter. This discussion describes some of the techniques that have particular application for reconstruction and salvage of the unique injuries of the specialized structures of the paws.

A unique wound affecting greyhounds is the digital pad callus/corn. These are painful lesions in need of a technique to resolve the condition.

Dorsal Paw Wounds

Some dorsal paw wounds may be such that the wound edges can be easily apposed after debridement and lavage. In other instances, tension in wound closure may need to be overcome by using some type of tension suture pattern, such as vertical mattress sutures, horizontal mattress sutures, or far near near far sutures. Other sutures can be used to relieve tension by gradually stretching the periwound skin so that it can be apposed or nearly so. Examples of these latter sutures are presutures and adjustable horizontal mattress sutures.

When wound tension is too great to be overcome by undermining, tension sutures, or skin stretching sutures, relaxing incisions can be considered when wound size permits. These are used in lieu of skin grafts or flaps. Simple relaxing incision(s) made adjacent to the wound can be used; however, such incisions commonly result in wounds about as large as the one that is closed as a result of their use. Multiple punctate relaxing incisions provide cosmetic and quickly healing small wounds while providing skin relaxation.

Although other familiar tension suture patterns and simple relaxing incisions can be used to aid in closure of dorsal paw wounds, this section describes presutures, adjustable horizontal mattress sutures, and multiple punctate relaxing incisions. These techniques have been found especially useful in closure of distal limb and dorsal paw wounds.

Presutures

Presutures are particularly useful in the distal limb and paws, in which “walking” sutures can encroach on vessels, nerves, and tendons. Presutures are thus termed because they are placed before excision or debridement of a lesion. They stretch the surrounding skin so that it can be used to close a distal limb or paw defect. Presutures are placed with interrupted Lembert bites, using 2-0 or 3-0 polypropylene or nylon suture (Figure 41-40A and B). They are placed under tension, usually 24 hours before excision or debridement. Presutures are placed while the animal is under the effects of a tranquilizer or neuroleptanalgesia and local analgesic agent in the skin to be sutured. Following presuturing, the area is bandaged until lesion excision or debridement.

At the time of definitive surgery, the presutures are removed. The lesion is removed or debrided, and the skin, which has been stretched gradually by stress relaxation, is used to close the defect (Figure 41-40C and D).

An advantage of presutures is that they can be used in conjunction with other tension relieving techniques to provide wound closure. Between the time they are placed and the time of removal, the limb should be observed for any swelling distal to the sutures. This swelling indicates the possibility of a biologic tourniquet developing at the time of definitive surgery, and another form of reconstruction may be considered.
 

Adjustable Horizontal Mattress Sutures

A continuous adjustable horizontal mattress suture may be used to aid wound contraction by applying continuous tension to the skin edges of a wound that cannot be closed initially because of tension. The suture may be placed early in wound management or after granulation tissue has formed.

Synthetic 2-0 monofilament suture (nylon or polypropylene) on a cutting needle is used to place a half buried horizontal mattress suture at one end of the defect. The suture is continued as an intradermal horizontal mattress suture along the length of the wound. Each suture bite is advanced slightly, so the suture passes at an angle across the wound. Thus, as the suture is tightened, it slides through the tissues more easily. Care is taken not to disturb the attachment of skin to any granulation tissue present in the wound. At the opposite end of the wound, the needle is passed through the entire skin thickness and through a hole in a sterile button. Traction on the suture moves the wound edges toward each other. The skin edge advancement is maintained by a small fishing weight (“split shot”) placed on the suture adjacent to the button. (Note: due to environmental concerns from lead, non-toxic split shot made from bismuth, tin, or antimony are now widely available, and should be used, to prevent the possibility of toxic lead exposure in the event of patient ingestion.) To prevent slippage, a second split shot is placed against the first (Figure 41-41). Excess suture is cut off about 2 inches beyond the split shot, and a bandage is applied over the wound.

On succeeding days, suture beyond the split shot is grasped with forceps, and gentle traction is applied while the limb is steadied. The wound edges move closer together, and the original split shot are pulled away from the button. Two new split shot are placed against the button to maintain suture advancement. Because of inherent skin elasticity, skin advancement is greatest in the first 2 to 3 days. When the wound edges are apposed or when they have advanced to their limit and further tension does not result in wound edge advancement or movement of the suture, the suture is removed.

Modified placement can be performed by placing the split shot button apparatus at both ends of the suture to allow tightening from both ends. With longer wounds, this maneuver is helpful because, the further the button is from the center of the wound, the less suture slippage through the tissues occurs. Therefore, pulling at each end of the wound distributes tension more evenly along the wound. During the use of an adjustable horizontal mattress suture, wounds can be treated with a topical antimicrobial or wound healing stimulant in combination with a protective bandage.
 

Multiple Punctate Relaxing Incisions

Multiple punctate relaxing incisions are small, parallel staggered skin incisions made adjacent to a wound to release tension and to allow wound closure. The surgeon may want to use presutures or an adjustable horizontal mattress suture before making these relaxing incisions.

A continuous intradermal suture of 3-0 synthetic absorbable suture material, such as polyglyconate or polyglactin 910, is begun at one end of the wound. If the skin edges do not appose or appose with tension while placing and tightening this suture, punctate relaxing incisions are made in the skin adjacent to the wound edges on both sides of the wound. These incisions are usually 1 cm from the wound edge, 1 cm long, and 0.5 cm apart. They are made in parallel staggered rows (Figure 41-42A). After the skin edges are apposed, simple interrupted 2 0 or 3 0 polypropylene or nylon sutures are placed in the wound edges (Figure 41-42B).
 

An alternate method for performing the procedure entails placing the continuous intradermal absorbable suture along the length of the wound, but not tightening or tying it at one end. Tension is applied to the free end of the suture, and hemostats are placed under a loop of suture near its origin. If the skin edges do not appose when the hemostats are elevated, bilateral punctate incisions are made in the area of tension (Figure 41-43A and B). The procedure is repeated along the suture line to bring the wound edges into apposition (Figure 41-43C and D). Final closure is with simple interrupted 2-0 or 3-0 polypropylene or nylon sutures (Figure 41-43E).
 

The more punctate incisions that are made and the larger they are, the greater the tension relief. However, the opportunity to damage the cutaneous vasculature is increased, thus increasing the risk of necrosis. Therefore, no more punctate incisions should be made than are necessary to provide wound closure without excessive tension.

The sutured wound is routinely bandaged, with daily changes in the early postoperative period to remove drainage from the wound site that occurs through the punctate incisions. A nonadherent primary bandage layer facilitates atraumatic bandage changes. As healing occurs and drainage decreases, bandages are changed less frequently.

Multiple punctate relaxing incisions break up the relaxing incision in numerous small incisions that are more cosmetic, heal rapidly, and are more acceptable to the animal’s owner. However, the amount of tension relief may not be as great as that attained by one large relaxing incision.

Pad Wounds

Wounds on the palmar or plantar surface of the paw often involve the digital, metacarpal or metatarsal pads. These wounds may be as simple as a minor laceration or as serious as the loss of an entire pad. Because the pads are subject to impact stress and frictional wear, surgical techniques and aftercare require some special features to ensure adequate healing.

Suturing Pad Lacerations

Suturing of pad lacerations is indicated when the edges of the traumatized pad can be apposed. Pad lacerations require special attention before closure, first to assess the depth of the laceration and second to determine the degree of contamination of the wound. These assessments may be facilitated by inserting the tips of a pair of hemostats into the wound and opening the jaws. Most wounds are partial thickness; however, some full thickness wounds of the metacarpal and metatarsal pads may expose the digital flexor tendons.

Because of the location and function of pads, they are subject to considerable contamination when weightbearing after injury forces contaminants into the tissues. Before suturing the pad, thorough debridement and lavage must be performed to remove dirt and other contaminants. If the laceration has extended through the entire metacapal or metatarsal pad, after lavage is completed, a small, soft, latex Penrose drain is placed under, not through, the pad.

Although the deep pad tissue may appear to be apposed, placement of deep simple interrupted sutures of 3 0 polydioxanone gives support to the tissues (Figure 41-44A). The superficial pad tissues are sutured with far near near far sutures of 3 0 nylon or polypropylene (Figure 41-44B).

A small amount of cotton is placed between the digits and in the space between the digits and the metacarpal or metatarsal pad to help keep these areas dry. A nonadherent bandage pad is placed over the suture line. The success of pad sutures in helping to provide early strong healing depends on proper bandaging to help prevent spreading of the pad during weight bearing. For a large dog where pad spreading with weight-bearing could cause significant tissue damage as sutures cut through the skin, the paw should be bandaged in a “clamshell” splint (see description in Chapter 2). The bandage is changed every 2 to 3 days unless a drain has been placed under the metacarpal or metatarsal pad. In this case, more frequent bandage changes are indicated to remove drainage fluid. Sutures are usually left in place for 10 to 14 days, depending on the severity of injury and the size of the animal; for example, a severe laceration on a large dog needs sutures and bandages longer than a minor laceration on a small dog.
 

Phalangeal Fillet

The phalangeal fillet technique is the removal of the proximal, middle, and distal phalanges from a digit to free the pad so it can be used to replace or fill defects in a metacarpal or metatarsal pad. The technique is indicated when conservative therapy has not resulted in effective healing of the pad or when the entire pad is missing.

In patients with chronic nonhealing metacarpal or metatarsal pad wounds that have not resulted from trauma, a thorough examination should be performed preoperatively. This should include cytologic examination, fungal and bacterial culture and sensitivity testing, as well as histopathologic examination. Appropriate medical and/or surgical therapy should follow if cultures reveal fungal or neoplastic disease. Surgical therapy may range from limb amputation to pad amputation and replacement (phalangeal fillet), depending on test results. If histologic examination reveals chronic nonhealing tissue, the wound should be thoroughly debrided and lavaged because the granulation tissue may have embedded dirt and sand.

Phalangeal fillet may be performed from the palmar or plantar surface of the paw. The digit nearest the metacarpal or metatarsal pad defect is selected for filleting. This is usually the second or fifth digit. A rectangular skin segment is removed from the palmar or plantar skin between the digital pad and the edge of the metacarpal or metatarsal pad defect (Figure 41-45A). The proximal, middle, and distal phalanges of the digit are removed by incising the joint capsules and ligamentous attachments to the bones (Figure 41-45B). The phalanges and nail are removed using blunt dissection as close to the bone as possible, thus leaving the blood and nerve supply intact in the digital flap. The edge and surface of the metacarpal or metatarsal pad defect are debrided, and the pad of the filleted digit is folded back on its pedicle of skin to fill the metacarpal or metatarsal pad defect (Figure 41-45C). The edges of the digital pad are sutured to the edges of the pad defect with simple interrupted or far near near far sutures of 3-0 polypropylene or nylon suture material (Figure 41-45D). The paw is bandaged as described for pad laceration repair.

A second technique for phalangeal fillet entails phalangeal removal through a single longitudinal incision on the dorsal surface of the digit (Figure 41-46A and B). The skin is then closed with simple interrupted sutures of 3 0 polypropylene or nylon suture material (Figure 41-46C). The area where the nail was removed is left open for drainage.

The paw is bandaged with periodic bandage changes, and it is allowed to heal for 14 days. At this time, the rectangle of palmar or plantar skin is removed, and the digital pad is folded back and is sutured into the defect as previously described (Figure 41-46D-F). Bandaging is as previously described.

Palmar or plantar filleting has the advantage of being a one step procedure; however, it is more difficult, and has greater potential for damage to the blood supply of the digital pad. Dorsal filleting is easier, but the technique takes longer because it is a two step procedure, with digital pad transposition performed 14 days after the phalanges have been removed.
 

In some instances, if a metacarpal or metatarsal pad wound has resulted from abnormal paw position because of tendon malfunction, bone misalignment or nerve damage, digital pad transposition may not be successful. Unless the underlying cause of abnormal pad wear is corrected, the new pad may wear through just as did the original pad.

Pad Grafts

Paw pad grafts are small full thickness segments of pad tissue that are placed in a granulation tissue bed around the edges of a wound where weight bearing pad tissue is missing. They are indicated in patients with loss of the metacarpal or metatarsal pad as well as loss of some or all the digital pads, thus precluding phalangeal fillet.

After a paw wound has been managed to the point that it has healthy bed of granulation tissue, rectangular tissue segments measuring 6 x 8 mm are traced around the wound using a template of x-ray film with a hole in its center and a sterile skin marker or splintered applicator stick dipped in methylene blue (Figure 41-47A). The rectangles of tissue are incised with a number 11 scalpel blade, and the tissue is excised using iris scissors and thumb forceps, leaving a series of rectangular depressions about 2 mm deep around the wound (Figure 41-47B and C).

In the center of other digital pads on the same animal, possibly the same paw, the same template is used to trace the same number and size of rectangles (See Figure 41-47C). Again, a number 11 scalpel blade is used to incise the grafts, and iris scissors and thumb forceps are used to remove the grafts (Figure 41-47D). All subcutaneous tissue is removed from the grafts with iris scissors.

A graft is placed in each of the rectangular depressions and sutured in place. Two simple interrupted sutures of 5-0 polypropylene can be used, with one suture on each side of the graft on the long sides of the graft (Figure 41-48A). An alternative suture pattern, which the authors prefer, is a simple interrupted suture placed at each corner of the graft (Figure 41-48B).

A nonadherent bandage pad with a small amount of 0.1% gentamicin sulfate ointment is placed over the grafted site. The remainder of the bandage is as described for pad lacerations. The graft donor sites are allowed to heal by second intention and are bandaged in a similar manner. If remaining digital pad tissue is pliable enough to allow suture closure of the donor sites, these sites may be closed with 3-0 polypropylene or nylon far near near far sutures followed by bandaging. The initial bandage is usually left in place for 3 days, followed by bandage changes every other day until 21 days postoperatively. A bootie may be indicated for a transitional period between bandage and no bandage. Sutures in the grafts are removed between 10 and 14 days postoperatively.
 

When sutures are removed from the grafts, the hard and dark stratum corneum usually lifts off of the graft to reveal underlying viable graft tissue that will form a new stratum corneum. As the grafts heal, two phenomena occur that provide a tough tissue on which the animal can ambulate. First, with wound contraction, the grafts coalesce toward the wound center. Second, the epithelial tissue that grows from the grafts to cover the remainder of the wound is tough keratinized epithelium that withstands the stress placed on pad tissue. If paw trauma has been severe enough so that bone is present directly under the healed pad grafts, weight bearing may cause pad trauma. Use of a pad toughening agent after the grafts are thoroughly healed has been found helpful in increasing pad durability.

Carpal Pad Flaps

Carpal pad flaps are flaps of skin on the distal forelimb that incorporate the carpal pad. They are used to provide a structure on which an animal can ambulate after amputation at the carpometacarpal articulation. These flaps may be single pedicle or bipedicle advancement flaps. Their successful use has been described in bilateral application on a small dog (single pedicle flap) and unilaterally on a cat (bipedicle flap).

Single Pedicle Carpal Pad Flaps

For a single pedicle advancement flap, a transverse skin incision is made over the cranial aspect of the limb at the carpometacarpal level. A proximally based single pedicle advancement flap is created on the palmar aspect of the limb such that it includes the carpal pad. The skin flap distal to the pad should extend to the mid-metacarpal level, to allow sufficient length for suturing the flap to the skin on the dorsum of the limb after advancement into position (Figure 41-49A).

After blunt dissection of the skin flap from underlying structures, the flexor carpi ulnaris tendon is transected, and the prominence of the accessory carpal bone is removed. The distal limb is then amputated at the carpometacarpal joint. The flap is advanced distally until the carpal pad is located at the caudodistal end of the amputation stump. The pad is anchored in position with subcutaneous simple interrupted sutures of 3-0 synthetic absorbable material, and the skin is sutured with simple interrupted sutures of 3 0 nylon or polypropylene (Figure 41-49B).

The limb is immobilized in a soft padded bandage with a metal (e.g. “clamshell”) splint. Sutures are removed and splinting is discontinued 2 weeks postoperatively.
 

Bipedicle Carpal Pad Flaps

For a bipedicle advancement flap, parallel horizontal skin incisions, one proximal to and one distal to the carpal pad, are made on the palmar aspect of the limb. The proximal incision is curved 2 to 3 mm proximally at each end to facilitate flap transposition (Figure 41-50A). After advancement of the flap under the end of the amputation stump, the flap is sutured in place with simple interrupted 3 0 nonabsorbable sutures. The palmar donor site is allowed to heal as an open wound (Figure 41-50B).

A padded splint is applied to the limb. A supplemental bar may be added to allow ambulation without disturbing the flap, or a “clamshell” bandage splint may be used. Periodic bandage or splint changes are performed until healing has occurred.

With successful carpal pad flap procedures, use by the patient results in thickening and enlargement of the pad. This provides functional weight bearing tissue.

Before performing carpometacarpal amputation and carpal pad flap repositioning, the animal’s activity and intended use, and the owner’s expectations after surgery should be considered. The technique has potential for use on larger dogs; however, accurate placement of the pad may be more critical when considering the greater weight to be placed on it. Moreover, when the procedure is performed unilaterally, that limb is significantly shorter than the other limb, and the animal may tend to carry the limb or only use it intermittently.
 

Digital Pad Calluses/Corns

Greyhounds are subject to the development of painful fibrous scar tissue lesions on their digital pads. These callus-type lesions have been termed “corns.” There are several theories as to their etiology. One theory is that of scar tissue accumulation, either from cuts and abrasions, or from a small foreign body in the pad with resulting scar tissue formation as the body attempts to isolate the foreign material. A second theory states that the lesion is caused by a papilloma virus infection, with the pressure and abrasion of walking forcing the lesion into a corn-type appearance. A third theory is that the phenotypic leanness of greyhounds is also manifested in their feet, by a lack of sufficient fibroadipose cushioning tissue in greyhound digital pads compared to other breeds of dogs. As a result, chronic low-grade pressure of the distal interphalangeal joint on the dermal pad surface results in a callus-like lesion.

Numerous treatments have been described for these lesions; the veterinary literature describes soaking of the paw and application of manual pressure to express the corn, sharp surgical excision of the corn, and partial or total amputation of the affected digit. A preliminary study has been performed to investigate the potential for placing silicone block gel particles subdermally under the digital pad skin to provide cushioning between the distal interphalangeal joint and the pad dermis, i.e., padding similar to the fibroadipose tissue of normal pads. Results of the study indicated a reduction in pad pressure at 3 months post-implantation.

Digital, Interdigital, and Interpad Wounds

Paw lesions may involve the interdigital skin or the interpad skin on the palmar or plantar surface of the paw. The lesions are usually traumatic or infectious. The phalangeal fillet technique and a fusion podoplasty technique may be used to reconstruct or to salvage paws thus involved.

Phalangeal Fillet for Digital and Dorsal Paw Resurfacing

The phalangeal fillet technique can be used as a salvage technique when patients have sustained considerable digital trauma to osseous structures of a digit with skin deficits of adjacent digits or the dorsum of the paw. If the digital and interdigital skin of the digit with osseous damage is viable, phalanges may be removed from the digit, and its skin and adjacent interdigital skin may be used to replace the skin deficit of the adjacent digits or dorsum of the paw.

The digits with severe osseous damage are carefully debrided, and the remaining proximal, middle, and distal phalanges and tendon fragments are removed (Figure 41-51A and Figure 41-52A). The skin of this digit and any available interdigital skin are cut and trimmed such that they can be used as a flap to resurface adjacent digits with large skin deficits or the dorsum of the paw (Figure 41-51B and C) and Figure 41-52B and C). The digital and interdigital skin should be cut and trimmed with care, to ensure that sufficient skin and subcutaneous tissue remain at the base of the flap to provide blood supply. The flap is sutured, to the remaining skin of the adjacent digits or dorsum of the paw with simple interrupted sutures of 2 0 or 3 0 polypropylene (Figure 41-51D) and Figure 41-52D).
 

Small amounts of cotton are placed between remaining digits and in the space between remaining digits and the metacarpal or metatarsal pad for dryness. A strip of nonadherent bandage pad is placed over suture lines. Absorbent secondary bandage and adhesive tape tertiary bandages are then applied. The cup of a metal splint may also be incorporated in the bandage. Clinical judgment should be used as to whether special considerations are needed in bandaging to relieve pressure on the area, i.e., “clamshell” bandage, foam sponge “donut” pad, or digit-elevating foam sponge pad (See Chapter 2). Bandages are changed periodically for 7 to 10 days. The length of time sutures should remain in place, the frequency of bandage changes, and the length of time bandages are needed are variable factors dependent on wound tension, wound healing rate, and amount of drainage.

The disadvantages of the procedure are that filleting of digit 3 or 4 leaves a cosmetic defect in the center of the paw, and a defect in this area can cause lameness. If digits 3 and 4 have been filleted to resurface digits 2 and 5 or the dorsum of the paw, the second and fifth digits protrude and may be subject to snagging on carpets or vegetation. If the pads of the filleted digits are needed for resurfacing procedures, they may be used; however, pad tissue in an abnormal location on the dorsum of the paw may be cosmetically unappealing.
 

Fusion Podoplasty

Fusion podoplasty is a paw salvage technique whereby all interdigital and interpad skin is removed from a paw, and the remaining strips of skin on the dorsum of the digits are sutured together, as are the digital and metacarpal or metatarsal pads. The technique is indicated for the treatment of chronic fibrosing interdigital pyoderma in dogs when other forms of medical therapy or conservative surgical approaches have been unsuccessful. The procedure is usually performed on two paws at a time when all four paws are involved. The most severely involved paws (usually the fore paws) are operated on first, followed 1 month later by the hind paws. The technique has also been described for use in treating abnormalities associated with severed digital flexion tendons to fuse the digits against the metacarpal or metatarsal pad to provide a functional paw.

When this technique is used to treat chronic fibrosing interdigital pyoderma, the dog is given systemic antibiotics based on the results of culture and sensitivity testing before the surgical procedure. At the time of surgery, a sterile marking pen is used to outline the interdigital skin to be removed. On the dorsum of the paw, lines are drawn on the digits at the junction of normal and affected skin. Lines are drawn near the nails, so 2 to 3 mm of skin remains adjacent to the nail on the axial surfaces of the digits.

Because the third and fourth digits extend beyond the second and fifth, respectively, lines on the abaxial surfaces of the third and fourth digits are drawn so they intersect the digital pad midway between their cranial and caudal ends. The technique provides skin excisions on the abaxial surfaces of the third and fourth digits that match the axial surface excisions on digits 2 and 5, respectively (Figure 41-53). This method usually incorporates all affected skin between the fourth and fifth as well as between the second and third digits.

On the palmar or plantar paw surfaces, lines are drawn to enclose all interpad skin and the cranial portion of the metacarpal or metatarsal pad. Lines are drawn around the caudal aspects of the digital pads at the junction of pad and interpad skin. No lines are drawn around the cranial edge of the pads under the claws or around the abaxial surface of pads 2 and 5. From the caudoabaxial aspect of the second and fifth digital pads, lines are drawn along the skin fold that extends from this point to the base of the metacarpal or metatarsal pad. The line is continued across the cranial surface of the metacarpal or metatarsal pad. This line is 3 to 5 mm cranial to the level at which the caudal edges of the digital pads contact the metacarpal or metatarsal pad when the digits are flexed back against this pad (Figure 41-54).

A half inch Penrose drain is applied as a tourniquet around the limb just distal to the carpus or tarsus. The tourniquet is released for 1 minute after all skin incisions have been made, and again after the excision of all interdigital skin is completed. A scalpel blade is used to incise along all previously drawn lines.
 

Starting at one dorsal interdigital cleft, interdigital skin is dissected from the cleft toward the cranial fold of this skin. Dissection is performed as close to the dermis as possible to avoid damage to the axial and abaxial dorsal and palmar or plantar proper digital vessels and nerves. When dissection becomes difficult near the fold of the web, dissection is discontinued and an adjacent interdigital space is dissected (Figure 41-55). After all interdigital spaces have been dissected, blunt and sharp dissection is done around the caudal aspects of the pads and along the palmar or plantar surface of each digit, again dissecting as close to the dermis as possible. At the base of the metacarpal or metatarsal pad, dissection of the dermis and epidermis is carried across the cranial surface of the pad from the lateral to the medial aspects of the pad. Underlying pad tissue is undisturbed (Figure 41-56). Deep connective tissue pockets containing exudate are carefully removed. After removal of the tourniquet, fine point electrocoagulation is used for hemostasis. The paw is soaked in a 0.05% chlorhexidine diacetate solution for 1 to 2 minutes. The paw is wrapped in a snug pressure bandage, and the procedure is repeated on the opposite paw.

After pressure wrapping the second paw, the pressure wrap is removed from the first paw. Adjacent digital pads are united with three simple interrupted 3-0 polypropylene sutures (Figure 41-57). The four united digital pads are flexed back against the cranial surface of the metacarpal or metatarsal pad. Simple interrupted 3-0 polypropylene sutures are placed alternately on either side of a central suture to affix the united digital pads to the metacarpal or metatarsal pad (Figure 41-58). The primary purpose of these sutures is to hold the digital pads in position against the metacarpal or metatarsal pad while the healing process begins in the deeper tissues.
 

Before placing the final two sutures on either side of the paw, the tips of a pair of curved Carmalt forceps are passed deep to the pad sutures across the cranial surface of the metacarpal or metatarsal pad. A quarter inch diameter Penrose drain is grasped and pulled through the wound. It is cut with a half inch protruding on each side of the paw. The drain is anchored in place by passing the final suture on each side through the skin and drain (Figure 41-59).

The skin strips on the dorsum of each digit are sutured together with three to four simple interrupted sutures of 3-0 polypropylene (Figure 41-60). Areas at the ends of the digits are not sutured, to allow for drainage. After suturing the first paw, the pressure wrap is removed from the second paw, and it is sutured in like manner.

Gauze sponges are placed on the dorsal and palmar or plantar surfaces of the paws. A thin layer of 0.1% gentamicin ointment may be spread on the gauze before it is applied. A “clamshell” splint bandage is applied over the paws (See Chapter 2). These splints go to the level of the elbow on the forelimbs, or to the hocks on the hind limbs. Bandages are changed daily as long as drainage is significant, usually 10 to 14 days. With decreased drainage, bandages are changed every second or third day until 21 days. A small amount of gentamicin sulfate ointment may be placed over the suture lines and at points allowed for drainage. When the bandage is changed, if the area has a characteristic odor of Pseudomonas, the paw may be soaked in 0.05% chlorhexidine solution before being rebandaged; a biguanide-impregnated gauze (Kerlix AMD, Kendall Healthcare, Tyco Healthcare Group, Mansfield, MA, USA) is also helpful for this.

Drain tubes are removed at 10 days. Sutures are removed from the dorsal paw skin and between the digital pads at 10 to 14 days. Sutures between the digital pads and the metacarpal or metatarsal pad are removed at variable times, depending on when the tissues appear healed or whether the sutures are still apposing tissues in patients with some tissue separation in this area. Generally, all sutures and splints are removed by 21 days. A light bandage or a protective bootie may be used for a period as a transition between full bandaging and no bandage.
 

The most common complication of the procedure is separation of the suture line between the digital pads and the metacarpal or metatarsal pad. The “clamshell” splint (See Chapter 2) helps to prevent this complication; however, separation may occur and can expose an area of granulation tissue. If it appears that individual sutures are not functioning to hold the digital pads against the metacarpal or metatarsal pad, these sutures are removed, and the area is allowed to heal as an open wound. A nonadherent bandage pad is used with the remainder of the bandage until the area has epithelialized, usually by 21 days.

Massive Digital Wounds - Pandigital Amputation

Pandigital amputation is a salvage operation in which all digits are amputated at the metacarpophalangeal or metatarsophalangeal level, and the metacarpal or metatarsal pad is positioned under the ends of metacarpal or metatarsal bones to provide a weight bearing tissue on which the animal can ambulate. The procedure is indicated in cases of severe damage to all digits as the result of pressure necrosis, phlebitis, trap injury, or other sources of trauma.

A transverse incision is made in the dorsal paw skin over the metacarpophalangeal or metatarsophalangeal articulation (Figure 41-61A). On the palmar or plantar surface of the paw, the incision is made at the junction of the metacarpal or metatarsal pad with the interpad skin (Figure 41-61B). If a line of demarcation is present between viable and nonviable skin on either surface of the paw, the incision should be made approximately 3 mm proximal to the line in viable tissue.

Working from the dorsum of the paw, the skin is reflected, and dorsal axial and abaxial common or proper digital vessels are ligated with 3-0 polydioxanone ligatures and are severed distal to the ligatures. Associated nerves, extensor tendons, collateral ligaments and metacarpophalangeal or metatarsophalangeal joint capsules are severed. The sesamoid ligaments are cut, and the sesamoid bones are removed on the palmar or plantar surface of the limb. The palmar or plantar common. or proper digital vessels are ligated and are severed along with associated nerves and flexion tendons. The digits are removed (Figure 41-61C). Bone rongeurs are used to remove the heads of the metacarpal or metatarsal bones if no infection is present.

Metacarpal or metatarsal bones, especially the third and fourth bones, are trimmed back until the metacarpal or metatarsal pad can be folded cranially and positioned such that the thickest part of the pad is directly beneath the ends of the metacarpal or metatarsal bones (Figure 41-61D). The skin edge on the dorsal surface of the metacarpal or metatarsal area may also have to be trimmed to get this positioning. If infection is present, the heads are not removed from these bones in an effort to avoid the possibility of ascending infection in the marrow cavities of the bones. After infection is controlled the area may undergo reoperation to remove the heads and trim the bones.

After the metacarpal or metatarsal pad has been folded cranially into position, a quarter inch diameter Penrose drain is placed between the pad and the ends of the bones. The pad is rotated under the ends of the bones. Interrupted horizontal mattress sutures of 2-0 or 3-0 polvglyconate or polyglactin 910 are used to suture the subcutaneous tissue on the cranial edge of the metacarpal or metatarsal pad to the subcutaneous tissue overlying the cranial aspect of the metacarpal or metatarsal bones after the pad is rotated into position (Figure 41-61E). Far near near far sutures of 2-0 or 3-0 polypropylene or nylon are used to complete the closure of the metacarpal or metatarsal pad to the skin on the cranial surface of the metacarpal or metatarsal bones. Simple interrupted tacking sutures are placed at each end of the drain to hold it in place (Figure 41-61F).

A “clamshell” splint is indicated when bandaging to keep pressure off of the newly positioned pad. The drain is removed in 4 to 5 days. Sutures are removed at 10 to 14 days, and bandage support is used for 21 days. These times are subject to variation, depending on healing and the size of the animal.
 

Occasionally, because of a combination of the way the animal bears weight and the lack of secure connective tissue fixation of the metacarpal or metatarsal pad to underlying structures, the pad may not remain in the desired position under the metacarpal or metatarsal bones, and ulceration may develop in an area adjacent to the pad. Repositioning of the pad and placement of fixation sutures under the pad may help to secure it in place. Placement of pad grafts in the area of wear may also be considered, and is preferred by the authors.

Suggested Readings

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Basher AW. Foot injuries in dogs and cats. Compend Contin Educ Pract Vet 1994;16:1159 1178.

Bradley DM, Shealy PM, Swaim SF. Meshed skin graft and phalangeal fillet for paw salvage: a case report. J Am Anim Hosp Assoc 1993;29:427 433.

Bradley DM, Swaim SF, Alexander CN, et al. Autogenous pad grafts for reconstruction of a weight bearing surface: a case report. J Am Anim Hosp Assoc 1994;30:533 538.

Newman ME, Lee AH, Swaim SF, et al. Wound healing of sutured and nonsutured canine metatarsal foot pad incisions. J Am Anim Hosp Assoc 1986;22:757 761.

Pavletic MM. Atlas of small animal reconstructive surgery, 2nd ed. Philadelphia: JB Lippincott, 1999:365.

Pavletic MM. Foot salvage by delayed reimplantation of severed metatarsal and digital pads by using a bipedicle direct flap technique. J Am Anim. Hosp Assoc 1994;30:539 547.

Swaim SF. Management and bandaging of soft tissue injuries of dog and cat feet. J Am Anim Hosp Assoc 1985;21:329 340.

Swaim SF. Wound management of distal limbs and paws: reconstruction and salvage. Vet Med Rep 1990;2:128 139.

Swaim SF, Amalsadvala T, Marghitu DB, et. al. Pressure reduction effects of subdermal silicone block gel particle implantation: A preliminary study. Wounds. 2004; 16:299-312.

Swaim SF, Bradley DM, Steiss JE, et al. Free segmental paw pad grafts in dogs. Am J Vet Res 1993;54:2161 2170.

Swaim SF, Garrett PD. Foot salvage techniques in dogs and cats: options, “do’s and don’ts.” J Am Anim Hosp Assoc 1985; 21:511 519.

Swaim SF, Henderson RA. Small animal wound management, 2nd ed. Baltimore: Williams & Wilkins, 1997:295.

Swaim SF, Lee AH, MacDonald JM, et al. Fusion podoplasty for the treatment of chronic fibrosing interdigital pyoderma in the dog. J Am Anim Hosp Assoc 1991;27:264 274.

Swaim SF, Marghitu DB, Rumph PF, et. al. Effects of bandage configuration on paw pad pressure in dogs: A preliminary study. J Am Anim Hosp Assoc 2003;39:209-216.

Swaim SF, Milton JL. Fusion podoplasty to treat abnormalities associated with severed digital flexion tendons. J Am Anim Hosp Assoc 1994;30:137 144.

Swaim SF, Riddell KP, Powers RD. Healing of segmental grafts of digital pad skin in dogs. Am J Vet Res 1992;53:406 410.

Vig MM. Management of integumentary wounds of extremities in dogs: An experimental study. J Am Anim Hosp Assoc 1985;21: 187 192.