Commonly Used Splinting and Casting Techniques

External fixation by coaptation implies the use of casts, splints, or bandages to provide immobilization of an injured limb. These devices approximate the shape of the limb to which they are applied, and they provide stable fixation of bone fragments without the need for surgical implants at the fracture site.

External fixation for orthopedic injuries in veterinary medicine offers distinct advantages over open reduction and internal fixation. In most instances, tissue and vascular trauma is reduced, the risk of infection is decreased, and the cost of application can be much lower than that of surgery.¹ Careful case selection is required to achieve successful treatment of fractures with external coaptation. In general, these devices are best used in young patients (less than 1 year of age) that tend to heal rapidly with transverse or incomplete fractures distal to the elbow or stifle. External coaptation best neutralizes bending forces on fractures away from joints, rather than near joints, and requires stabilization of the joint above and the joint below the fracture.² Therefore, coaptation does have disadvantages resulting from long-term limb immobilization that can cause severe disuse atrophy and possible “fracture disease.” The use of a below-the-knee cast bracing (Sarmiento-type) system has been advocated; if properly used for certain tibial fractures, this type of system may reduce problems associated with total immobilization of the hind limb.^3,4 If a coaptation device is incorrectly applied, loosens, or becomes wet, skin necrosis and even gangrene can result. Certain cases of multiple or severely comminuted fractures are best managed by internal fixation techniques, because precise anatomic reduction and adequate neutralization of forces acting on the fractures cannot be achieved with external coaptation.

Indications

Coaptation splints are commonly used for immobilization of simple transverse fractures of the radius, ulna, fibula, metacarpals, metatarsals, and phalanges. They can also be useful for immobilization of certain joints, such as the stifle, after traumatic injuries or surgical stabilization.^2,5 With most fractures, however, use of both internal fixation and external coaptation combines the disadvantages of both and, in general, should be avoided whenever possible.¹

Temporary coaptation devices usually are indicated in the acutely traumatized animal for prevention of edema, relief of pain, reduction of subsequent damage to soft tissue, wound protection from further contamination, prevention of development of closed fractures into open fractures, and fracture stabilization. Robert Jones bandages, coaptation splints of various materials, Schroeder-Thomas splints, tape hobbles, Ehmer slings, Velpeau slings, and nonweightbearing slings have been described for temporary immobilization as well as for definitive immobilization of certain orthopedic injuries.

The choice of coaptation device depends on each individual case and circumstance. The coaptation device may serve as a temporary splint for traumatic injuries while waiting for definitive internal fixation, as a primary treatment of certain fractures, or as an adjunct to internal fixation or ligament repair.^1,2 Cost is another important aspect that must be considered as well as the availability of materials required for different coaptation devices.

General Application Guidelines

A few general guidelines are relevant to application of all types of coaptation splints and casts. Depending on the animal’s physical condition and the severity of the orthopedic problem, application of coaptation splints or casts is best performed with the patient sedated or under general anesthesia. When the patient’s physical status precludes the use of chemical restraint, traction and excessive manipulation of the limb must be kept to a minimum.

Use of Stirrups

Application of adhesive tape on the cranial and caudal surfaces of the foot to form “stirrups” is usually necessary so the limb can be attached to the splint or cast securely (Figure 64-1A). In some instances, one should fix the strips of adhesive tape medially and laterally on the limb; this has been recommended for application of a full-encircling cast.⁶ When lateral and medial stirrups are used, they must be incorporated into the lateral and medial sides of the cast, respectively, to avoid excessive pressure and possible skin necrosis over the outer distal metatarsal or metacarpal epiphyseal areas.⁷ Encircling bands of tape should never be used on an animal’s foot because they can cause irreparable vascular damage and skin necrosis.

If problems are encountered in attaching the tape to the foot, the skin can be dried with alcohol to increase the holding capacity on the foot. Some veterinarians spiral a piece of adhesive tape around the cranial and caudal tape pieces to increase fixation of stirrups to the skin.⁸ Two to three overlapping layers of elastic gauze (Kling or Sof-Kling, Johnson & Johnson Medical, Inc., Arlington, TX) applied snugly and evenly over the stirrups has also been used without problems to prevent the tape stirrups from slipping (Figure 64-1B). Good judgment must be used during application of these gauze layers to prevent vascular compromise. Tape application over the carpal pad can cause mild irritation to this structure at the time of tape removal, but it is usually not severe.

A technique described specifically for cats uses longitudinal “anchor” strips of adhesive tape applied medially and laterally on the leg, with the tape ends extending proximal and distal to the bandage or splint. The exposed ends of the tape anchor strips are reflected back on the bandage and then are covered with a second layer of bandaging material, which locks the anchor strips on the bandage.⁹

Use of Padding

The padding layer of the bandage provides protection, absorbency, and minimal support to the limb, depending on the thickness of the padding layer. The use of padding before cast or splint application may ensure patient comfort, but when used inappropriately or in excess, it may actually decrease a device’s ability to provide adequate immobilization. Excessive padding, hair, and soft tissue structures increase the distance between the rigid part of the coaptation device and the rigid part of the limb (bone), and this can decrease the stiffness and effectiveness of the cast or splint. Therefore, long hair should be clipped, but not shaved, before bandage placement, and adequate cast padding should be applied to provide comfort and to prevent skin irritation. Hohn has stated that properly applied cast padding actually enhances fracture fixation by compensating for slight tissue shrinkage after cast application.⁶

One or two layers of orthopedic stockinette often are adequate; in some cases, incorporation of hair with the encircling plaster during the cast application may provide enough padding to prevent chafing and pressure sores as well as slippage. Removal of a plaster cast in which hair is securely incorporated can be difficult, however. Although some veterinarians apply small pieces of cotton between the toes before cast or splint application, an excess of padding can lead to additional vascular compromise.

Cast padding is applied, beginning at the toes, by overlapping half of the roll’s width as it is unrolled; it should be wrapped snugly but not tightly (See Figure 64-1B). Cast padding applied in this manner provides two layers of padding, which is normally adequate. Pressure points over humeral or femoral condyles, olecranon, tuber calcis, or carpal pad may be padded with an extra piece or two of padding, although Swaim and colleagues noted that applying full-length cast padding provided the best form of protection from dermal pressure injury.¹⁰
 

Limb Positioning

During application of any coaptation–in particular plaster, fiberglass, and thermolabile plastic casts–for immobilization of a front or rear leg, the limb should be placed in a functional position while the material is still moldable. The rear leg should be kept in a normal position with the hock slightly flexed. When the casting material is conformed to the shape of the front leg, the carpus should be placed in slight flexion (15°) and deviated medially by 15° (Figure 64-2). This positioning helps to prevent a valgus deformity, which otherwise could occur during manipulation because of the normal laxity of the radial carpal joint or as a result of eccentric growth of the radius and ulna in the immature patient. External rotation of the metacarpus should be avoided, and the foot should be kept in a neutral position.^4,11 The old adage expressed by some experienced clinicians, “crooked leg in, straight leg out; straight leg in, crooked leg out,” succinctly summarizes the preceding guidelines concerning proper limb position during cast application.
 

Coaptation Splints

Coaptation splints consisting of various rigid materials are used to approximate the shape of the limb to which they may be applied. In general, they should not be used for immobilization of the humerus or femur. Pre-made commercial splints consisting of plastic or aluminum are known as Mason metasplints or spoon splints. They are applied over padding on the caudal aspect of the limb. Because the limb is curved and the splint is straight, adequate padding is necessary to avoid soft tissue problems, but it may result in poor immobilization. Molded splints of plaster, water-activated fiberglass, or thermolabile plastic can be fitted to the limb almost perfectly. For this reason, they seem to be tolerated better by the patient and cause fewer soft tissue problems during long-term use than Mason metasplints.

Preformed Splints

Indications

Metasplints for the front or rear leg are primarily indicated for fractures of the distal radius and ulna, fracture-dislocations of the carpus or tarsus, and fractures of the metacarpal or metatarsal bones or phalanges. Stabilization of proximal radial or ulnar fractures usually is not adequate with these devices. Generally, the elbow joint cannot easily be immobilized without using a spica configuration over the shoulder.

Application Technique

Adhesive tape stirrups are applied on the cranial and caudal aspects of the paw, with the cranial tape extending beyond the paw 2 to 3 inches farther than the caudal tape. The tape ends are then pressed together. A piece of precut cotton is applied to the back of the paw and antebrachium, or the leg is wrapped with at least two layers of cast padding, even if the splint is foam padded. The splint is snugly secured to the limb with elastic gauze by wrapping the leg with firm conforming pressure beginning at the toes and extending proximally up the limb. The stirrups are reflected up the caudal aspect of the splint and are secured with tape or another layer of elastic gauze (Figure 64-3A). The “gauze-covered” splint is covered with adhesive tape, elastic tape (Elastikon, Johnson & Johnson, Medical, Inc.), or conforming elasticized tape (Vetwrap bandaging tape, Animal Care Products/ 3M, St. Paul, MN) (Figure 64-3B). If the splint extends only to the elbow joint, a V-shaped section can be cut from the cranial aspect of the bandage material just below the joint to prevent pressure necrosis in that area (Figure 64-3C).
 

Some clinicians apply metasplints by an alternative method that does not involve use of tape stirrups. With this method, slippage of the splint is prevented by wrapping tape proximally around the elbow to prevent flexion (Figure 64-4). The toes are left exposed, so circulation can be assessed.
 

Molded Lateral Splints

Indications

A molded splint applied laterally on either the forelimb or the rear leg can provide immobilization of the elbow joint or stifle, respectively. It can also stabilize less severe fractures of the radius, ulna, tibia, and fibula. This type of coaptation can be particularly helpful in providing protection from bending forces after internal fixation or joint stabilization. The casting material can be extended over the shoulder or hip as a modified spica to provide partial joint immobilization.

Application Technique

Adhesive tape stirrups may not be necessary for application of this type of splint, especially if it extends proximally to include the shoulder or hip. The patient is placed in lateral recumbency with the injured limb positioned uppermost. The limb is padded with two layers of cast padding beginning at the toes and ending at the axilla or inguinal area.

If the shoulder or hip is to be immobilized through the use of a modified spica splint, the layers of padding should encircle the chest wall or pelvis, respectively. For splint application on the front leg, the padding creates a figure-of-eight pattern around the thorax and the affected limb, but the padding and the next layer of conforming gauze are carried behind the opposite axilla (Figure 64-5A). For a hip spica, the cast padding and conforming gauze applied to the affected leg and the opposite limb create a figure-of-eight pattern and can incorporate the proximal half of the opposite leg. When this configuration is used, the resulting coaptation device is called a “one-and-a-half leg” spica.⁴ Care must be taken when applying a hip spica on a male dog so the prepuce is not included in the bandage. Spica splints are also restrictive, and some animals may not be able to stand without assistance.

Cast materials that can be molded to form a lateral splint are plaster, water-activated fiberglass, thermola-bile plastic, or yucca board. Rolls of plaster, water-activated fiberglass materials, or thermolabile plastic can be cut to proper length or shape before application on the lateral aspect of the limb after activation. Elastic gauze is used to conform the softened splint material to the limb and to attach the splint to the shoulder and chest wall or the hip and thigh area. The gauze-covered splint is then bandaged with elastic tape applied in a pattern similar to that of the gauze (Figure 64-5B and 64-6).

Conformable materials used for molded lateral splints should be applied according to the manufacturer’s directions and as each individual case dictates. A splint thickness of four to five layers of fiberglass or plaster casting material is usually adequate for the small animal patient. Prepackaged fiberglass splints are commercially available (Ortho-Glass Splinting System, Parker Medical Associates, Charlotte, NC) as well as unitized plaster splints (Specialist J-Splint plaster roll immobilizer, Johnson & Johnson Orthopaedics, Rayn-ham, MA). These products consist of multiple layers (8 to 15) of casting tape enclosed in a stockinette, which is packaged in a roll and can be cut to any length. Sheets of fabric impregnated with a thermolabile plastic (Orthoplast Splint Johnson & Johnson Orthopaedics) can be shaped according to a paper pattern of the affected limb and then softened in hot water (170°F) before application. Rolls of casting material composed of loosely knitted fabric impregnated with thermolabile plastic (Hexalite, Kirschner All Orthopedic Appliances, Marlow, OK) can be cut into splints as described earlier. The rigidity of this material requires that a flve-to six-layer splint be used to immobilize a limb adequately. To provide as much strength as possible, splint width of each coaptation material should be approximately one-third to one-half the outside circumference of the affected limb. In other words, the splint configuration is similar to a full-encircling cast cut in half in a cranial-to-caudal direction, with the lateral half of the cast used as the coaptation device.
 

Schroeder-Thomas Splints

Probably the most misused and misunderstood coaptation device today is the Schroeder-Thomas splint. When correctly applied, this splint can be an excellent means for immobilizing joints postoperatively surgery and for immobilizing certain fractures. This traction device can provide accurate and continued fixation of bone fragments by counteracting muscle forces and immobilizing parts of the skeleton. Under certain circumstances, skeletal traction can be provided when transfixation pins located in the areas of the femoral or humeral condyles are incorporated into the splint so traction from the splint on the distal end of the affected limb controls the distal fracture fragment.

Indications and Possible Complications

The use of Schroeder-Thomas splints may be indicated for some fractures of the radius, ulna, and tibia; avulsion fractures of the tibial tuberosity and distal malleolar fractures are exceptions. These splints have been used for fractures of the distal humerus (distal one-third), although not for condylar fractures, which require precise reduction of the joint surface to avoid degenerative joint disease. Nonarticular fractures of the distal femur (distal one-third) are considered by some clinicians to be amenable to reduction and immobilization with a Schroeder-Thomas splint, although supracondylar or condylar fractures must receive superb postreduction care because immobilization can be difficult to maintain. The splint has been used for temporary immobilization of the stifle and elbow joints postsurgically.

Although a Schroeder-Thomas splint can be used successfully for more orthopedic conditions than are mentioned here, its inappropriate use can have disastrous consequences.

Application to a fracture of the proximal humerus or femur is definitely contraindicated because the ring of the splint must support and rest on the proximal fracture fragment. If the splint is used for proximal femoral and humeral fractures, the ring rests in the fracture site and acts as a fulcrum point, whereas the limb serves as the lever resulting in movement at the fracture site. In these circumstances, fracture disease (nonunion, quadriceps tiedown, joint stiffness) results. The splint often loosens with time because of the dynamic nature of its application. Circulatory problems causing tissue necrosis can develop as a result of loosening, swelling of the limb, or improper application. Pressure necrosis under the ring of the splint, edema of the scrotum, severe limb edema, and strangulation of the foot can occur.

Application Technique

Schroeder-Thomas splints should be custom-made for every individual case. Obviously, splint rods can be reused if they are the appropriate length for an individual patient. Because this type of splint is a dynamic traction device, it requires careful attention by the owner and periodic adjustment by the clinician. A Schroeder-Thomas splint is constructed of aluminum rods (1/8-, 3/16-, or 3/8-inch diameter) available in 6-foot lengths or 12-foot coils. For small dogs or cats, regular coat-hanger wire has been used. An average-size dog (30 to 40 lb) requires the 3/8-inch diameter aluminum rod. Commercially available plastic or wooden “ring” blocks usually are used to form the elliptic ring at the proximal end of the splint. Adhesive tape and combine roll or elastic gauze are used for application of the stirrups and the traction slings, respectively. A vise is helpful in shaping the rod, and bolt cutters or a hacksaw are necessary for cutting the rod. The shape of the splint is modified in relation to the specific leg injured, the bone that is fractured, or the joint that is involved. Traction application also varies according to the fracture, so the fragments can be separated and aligned (Figure 64-7).

The first step in construction of a Schroeder-Thomas splint is the formation of the upper ring at the proximal end of the splint. For the rear leg, the diameter of the ring is determined by measuring the distance between the cranial aspect of the wing of the ilium and the caudal point of the ischium; for the foreleg, the ring diameter can be determined by measuring the length of the scapular spine.⁴ The bottom of the ring should be flattened to conform to the animal’s axillary area or thigh. The bottom of the ring must bend medial to the vertical bars at a 45° angle at the middle of the ring. The ring can be bent, or the vertical bars can be bent to accommodate this angle. The lower half of the ring should be padded; however, excessive padding may cause irritation and circulatory problems and should be avoided. Applying tape to the ring with the adhesive side facing outward and then wrapping the lower half of the ring with thin strips of cotton or cast padding work well. The tape with the adhesive side inward is applied over the cotton loosely so the padding is soft and conforms to the inguinal or axillary region.
 

The vertical bars of the splint are sometimes left straight to accommodate certain fractures. However, each case should be considered on an individual basis and the splint configuration varied accordingly. For the rear leg, the front bar is bent to conform to the normal angulation of the stifle and hock; the rear bar is left straight. The angles of the front bar are varied according to the injury (See Figure 64-7). For the fore-limb, both bars are bent to conform to the angulation of the elbow. Although various configurations for humeral and radioulnar fractures have been described,^4,8,12 the configuration illustrated in Figure 64-7A has been used successfully and seems to be well tolerated by most animals.

The vertical bars are bent and connected with adhesive tape at the bottom of the splint. The length of the splint is determined by gently extending the limb so the end of the splint coincides with the end of the toes. The limb should not be stretched taut in a Schroeder-Thomas splint. The middle of the horizontal bar formed by connecting the vertical bars can be bent into an inverse-V shape so the adhesive tape stirrups fastened there will not be worn away by walking. A separate piece of aluminum rod can also be added to the bottom of the splint to protect the tape. The width of the distal end of the splint should be approximately three times the width of the paw. The finished splint should be completely wrapped as smoothly as possible with adhesive tape for cosmetic purposes. More important, this procedure prevents slippage of traction slings. The completed splint is applied to the leg carefully, with the ring snugly placed in the axillary or inguinal area. The splint is secured initially to the distal end of the foot by means of an adhesive tape stirrup. For additional support, a spiral of tape (“barber pole”) can be applied over the foot to help secure the vertical stirrups. Wrapping tape circumferentially around the foot usually causes swelling and should be avoided. Cotton can be used to pad between the toes. The adhesive tape stirrups should not be used to apply traction.

Traction is applied by means of the combine roll or wide elastic gauze used to secure the leg to the vertical bars of the splint. Both products, but especially the elastic gauze, must be used with caution, because the application of excessive tension can cause necrosis or edema. Positioning of the traction slings depends on the nature of the fracture. For fractures of the tibia, the traction slings are placed around the hock joint first and then in the femoral area to provide traction on the tibia (See Figure 64-7B). For distal femoral fractures, the first traction sling is applied around the hock joint, and then one is applied around the proximal tibia to provide traction on the femur. Traction slings should be applied in such a manner that they provide adequate medial support to both the tibia and femur and avoid a valgus deformity of the limb.⁴ For fractures of the front leg, a traction sling is first applied at the level of the elbow, pulling the humerus caudally. The second sling is applied at the level of the carpus, pulling it cranially, which increases the traction on the radius, ulna, or humerus. As Figure 64-7A illustrates, tension can be applied caudally on the radius and ulna; a support sling placed in the area of the distal humerus maintains even pressure on the limb and reduces motion.

The entire Schroeder-Thomas splint can be covered with orthopedic stockinette to protect the device.

Postapplication Care

Excellent client and professional care is essential in maintaining a Schroeder-Thomas splint after application. The limb must be kept dry and clean, and the animal must be confined. Scheduled rechecks should be performed on a weekly basis, and clients must be diligent in evaluating the device for loosening, irritation, or swelling of the limb. If mild edema does occur, the animal must be monitored carefully for the next 24 to 48 hours; the splint may have to be adjusted or removed if this swelling persists or becomes more severe. Clients must be informed that reevaluation of the device whenever one suspects a problem is essential for proper splint management.

Tape Hobbles

Tape hobbles have been advocated as a method of protecting an injured limb and preventing additional trauma. This device can limit rotational stress on the limb and can aid in preventing stresses to proximal humeral or femoral fractures. It can also prevent excessive adduction or abduction of limbs with scapular or pelvic fractures. Hobbles must be used with caution when any possibility of vascular impairment or swelling in the areas of the metatarsus or metacarpus exists. The first step in application of tape hobbles is wrapping of two or three layers of cast padding around the metatarsal or metacarpal areas. Adhesive tape, 1 or 2 inches in width (depending on the size of the dog), is carefully wrapped around the paw to form a sling. One must not wrap the tape tightly around the paws. Overlapping the tape ends unevenly to form a “tab” from each foot should be the desired goal. The two tape tabs are joined with additional stirrups of tape. Usually, the distance between the feet is about that of a normal standing position for that animal, which should allow for proper freedom of movement (Figure 64-8).
 

Velpeau Sling

The Velpeau sling is used for immobilization of the shoulder joint postsurgically, for stabilization of the shoulder joint after closed reduction of luxations, for immobilization of scapular fractures, and for other conditions that require a front leg to be non-weight-bearing. A Velpeau sling should not be used on animals with oblique fractures of the distal humerus because compression by the sling may result in overriding of the fractured fragments and damage to the radial nerve. Olecranon fractures are also not amenable to this type of sling. A Velpeau sling is made of elastic gauze (2, 3, or 4 inches wide, depending on the size of the animal) or combine roll. It is started by loosely wrapping the conforming material around the paw in a lateral-to-medial direction. The wrap is continued laterally over the affected limb and shoulder and is placed around the thorax and behind the opposite axilla (Figure 64-9A). With the elbow, carpus, and shoulder joints flexed, the wrap is continued to the starting point. Several more layers of conforming material are applied in a similar pattern, but these layers enclose the elbow and paw (Figure 64-9B). Covering the entire limb prevents the lower limb or elbow from being forced out of the bandage if the animal tries to extend or flex the leg. The entire bandage is then covered with elastic tape in a similar manner.
 

The clinician must make the client aware that if the sling loosens and slips, besides the loss of immobilization, disastrous vascular impairment can occur. The animal should be strictly confined for the duration of the bandage’s application. Animals usually tolerate the sling well, but it should be checked on a weekly basis. If it is used more than 2 weeks for immobilization, joint contracture can occur because the shoulder, elbow, and carpal joints are held in severe flexion.

Postapplication Management of Splints, Casts, and Slings

After application of any splint, cast, or sling, the limb should be observed every 4 to 6 hours to be certain that the device has been applied correctly. If it is constricting vasculature or lymphatic drainage and causing the proximal or distal aspects of the limb to swell, the device should be removed immediately and reapplied. At the time of discharge, clients must be educated in the proper care of the coaptation device. The splint or cast should be kept dry at all times. Cornstarch or talcum powder can be used to prevent chafing and pressure sores where the device irritates the axillary or inguinal areas.

Clients must feel free to seek professional advice concerning the coaptation device. If any of the following problems should develop, the animal must be examined as soon as possible:⁴

1. Any sign of excessive discomfort
2. Any changes in position or shape of the splint or cast on the leg
3. Any unusual foul odors coming from the splint or cast
4. Any unexplained soiling of the splint or cast that was not present previously
5. Any sores that develop at the top of the splint or cast that do not respond to talcum powder or cornstarch application
6. Swelling of the toes or the leg above the coaptation device
7. Inappetence, depression, or fever in the animal
8. Any excessive chewing of the splint or cast

No splint or cast can be worn in complete comfort by an animal. Minor licking and chewing can be expected; however, when an animal continues to mutilate the device, the device should be rechecked. If it has been properly applied and the animal continues to chew the splint or cast excessively, properly applied chemical or mechanical restraint devices may be needed separately or in combination.¹³

References

1. Tomlinson J. Complications of fractures repaired with casts and splints. Vet Clin North Am 1991;21:735-744.
2. Leighton RL. Principles of conservative fracture management: splints and casts. Semin Vet Med Surg 1991;6:39-51.
3. Manziaro CF, Manziaro JR. Walking plaster cast for repair of tibial fractures in dogs. J Am Vet Med Assoc 1970;156:581.
4. Nunamaker DM. Methods of closed fixation. In: Newton CD, Nunamaker DM, eds. Textbook of small animal orthopedics. Philadelphia: JB Lippincott, 1985.
5. DeCamp CE. External coaptation. In: Slatter D, ed. Textbook of small animal surgery. 2nd ed. Philadelphia: WB Saunders, 1993.
6. Holm RB. Principles and application of plaster casts. Vet Clin North Am 1975;5:291-303.
7. Leighton RL. Complications from mismanagement of fixation devices. Vet Clin North Am 1975;5:273.
8. Knecht CD, Allen AR, Williams DJ, et al. Casts and splints for small animals. In: Fundamental techniques in veterinary surgery. 2nd ed. Philadelphia: WB Saunders, 1981.
9. Robinson GW, McCoy L, Gili M. Feline bandaging and splinting. Feline Pract 1977;7:41.
10. Swaim SF, Vaughn DM, Spalding PJ, et al. Evaluation of the dermal effects of cast padding in coaptation casts on dogs. Am J Vet Res 1992;53:1266-1272.
11. Tobias TA. Slings, padded bandages, splinted bandages, and casts. In: Oimstead ML, ed. Small animal orthopedics. St. Louis: CV Mosby, 1995.
12. Knecht CD. Principles and applications of traction and coaptation splints. Vet Clin North Am 1975;5:177.
13. Seim HB, Creed JE, Smith K W. Restraint techniques for prevention of self-trauma. In: Bojrab MJ, ed. Current techniques in small animal surgery. 2nd ed. Philadelphia: Lea & Febiger, 1983.

Suggested Readings

Arnoszky SP, Blass CE, McCoy L. External coaptation and bandaging. In: Slatter DH, ed. Textbook of small animal surgery. Philadelphia: WB Saunders, 1985.

Brinker WO, Piermattei DL, Flo GL, eds. Principles of joint surgery. In: Handbook of small animal orthopedics and fracture treatment. Philadelphia: WB Saunders, 1983.

Leighton RL. Principles of conservative fracture management: splints and casts. Semin Vet Med Surg 1991;6:39-51.

Tobias TA. Slings, padded bandages, splinted bandages, and casts. In: Oimstead ML, ed. Small animal orthopedics. St. Louis: CV Mosby, 1995.
 

The purpose of a cast is to provide rigid external coaptation to a reduced fracture or tenuous ligament repair so proper alignment and support are maintained during healing. Since 1851, the traditional plaster of Paris cast has been used when rigid external coaptation is required. Plaster casts provide an inexpensive means of providing molded external support, but they have the disadvantages of prolonged drying time, relative heaviness, decreased porosity, deterioration if exposed to moisture, and brittleness.¹ Synthetic casting materials have been developed and are available to veterinarians. The newer synthetic materials include polyurethane resin-impregnated fiberglass or polyester-cotton knit, and thermolabile plastic. These materials have the advantages of being lightweight, less bulky, immersible, radiolucent, and quickly “set,” but they are more expensive and can be difficult to mold. Although newer methods of internal fixation (bone plates and screws) are indicated for most complicated orthopedic problems, closed reduction and external coaptation can be the treatment of choice for selected fractures and ligamentous injuries. Long leg casts are most appropriate for fractures below the elbow and stifle that only require bending and rotational stability, such as incomplete or transverse fractures. The joint should be immobilized above and below the fracture in most cases, although functional below-the-knee casts have been used successfully.² Fractures of the humerus and femur require a cast in a “spica” configuration that immobilizes the shoulder or hip, respectively.

Plaster Casting Material

Characteristics

Plaster of Paris can be shaped and molded with ease and should usually be chosen for immobilizing severely displaced or unstable fractures that require a closer fit when coaptation is indicated. Because plaster is less expensive than the newer synthetic materials, it is indicated if frequent changes of casts are required. It is suitable for an initial or primary cast after fracture reduction when mild edema or swelling of a limb can be expected, because a change of cast is usually necessary after the edema subsides or becomes more severe.³ Synthetic casts should be used with small patients requiring a lighter cast, with patients likely to abuse or moisten the cast, or when a plaster cast is likely to fail within the required time of immobilization.

Plaster of Paris is made of calcium sulfate crystals that have been reduced to powder and subjected to intense heat to expel the water. The resulting chalky white powder is then incorporated into gauze bandages. When water is added to the plaster, a crystallization process occurs, and the material hardens in an exothermic reaction. The time from which water is added to the plaster bandage until the material becomes hard is called its setting time. Plaster sets in 3 to 8 minutes, depending on whether it is fast or extrafast setting, the temperature of the water used, and the amount of water left in a roll after immersion. As the cast dries, the interlocking of the calcium sulfate crystals gives the plaster its strength. Further molding after a plaster cast has begun to set can prevent this interlocking of the crystals and may weaken the cast.

After the cast sets, the excess water must evaporate from the surface before the cast attains maximal strength. This period (curing time) while the cast is still “green” varies from 8 to 48 hours, depending on how large and thick a cast is, the type of plaster used, humidity, and air temperature. Excessive weight-bearing during drying of the cast should be avoided. A plaster cast is heavy at first, but it becomes lighter as the water in the plaster evaporates. The strength of a plaster cast is proportional to its thickness, but the smallest possible amount of plaster should be used. Placement of plaster “splints” or reinforcing strips of cast material along one surface strengthens a cast without increasing its entire mass; this technique is especially useful over areas where angulation occurs and the cast is susceptible to stress and fracture.

Application Technique

No special equipment is required for preparation and application of a plaster cast, and a standard cast cutter can be used for removal. Gloves should be worn during application, because plaster can be irritating to the hands. The patient and casting area in the hospital should be protected from dripping plaster by the liberal use of newspaper or a plastic drop cloth.

Preparation of plaster bandages involves immersing them in tepid water (70 to 75°F) for a few seconds until the bubbling from the roll has stopped; the plaster rolls then are squeezed to remove excess water. A plaster bandage should be unrolled on the leg, as it is applied, in an encircling manner with overlapping of half of the roll’s width; it should never be stretched or tightened around the limb. It should be applied in a smooth, conforming manner so no thick or thin spots result. Tucks can be made in the rolls to change directions or to contour the plaster smoothly. Molding the cast by rubbing each section with wet hands before the plaster is set is essential for proper lamination, to produce a smooth surface, and for conforming the material to the proper configuration of the affected limb. During application, the cast should be supported by the palms of the hands and not indented with the fingers, because the “dimples” that result could produce pressure points on the interior, which can lead to skin excoriation.

Once the cast is dry, any rough edges should be covered with adhesive tape. The cast should not be washed, although a damp cloth can be used to remove excessive dirt if the residual moisture is wiped away afterward. Immersion of the plaster cast can cause deterioration of the plaster, resulting in skin irritation and maceration.

Some manufacturers (Duracast, Duraflex, Carapace, Caraflex, Cellona, Carapace, Inc.. Tulsa, OK; Gypsona, IMEX Veterinary, Inc., Longview, TX) supply plaster casting material in various widths (2, 3, 4, and 6 inches) and setting times (slow, medium, fast, and extrafast). For small animals, the 2- and 4-inch widths are the most versatile; fast or extrafast setting times are more appropriate for veterinary patients. Various setting times can be achieved by adjusting the temperature of the water in which the plaster bandages are immersed before application. Use of colder water increases setting times, and use of warmer water decreases it. Because plaster of Paris products are significantly less expensive than the newer synthetic materials, they will continue to be an essential moldable coaptation material.

Synthetic Casting Materials

Characteristics

Several newer synthetic cast materials are available as alternatives to plaster of Paris. These newer materials are recommended for use as primary casts for nondis-placed fractures with minimal swelling or for longterm wear when multiple cast changes are not required.^1,3-7 They can be divided into three classifications according to their composition: polyester-cotton knit, fiberglass, and thermolabile plastic. Manufacturers are introducing new materials every year, and each product obviously is recommended over a competitor’s for many different reasons. Clinicians should be aware of the advantages and disadvantages of several of the materials and should choose the one with the characteristics they regard as the most important.

Polyester-cotton casting materials consist of a polyester and cotton, knitted, open-weave fabric impregnated with a water-activated polyurethane resin (Delta-Lite Fabric Casting Tape, Johnson & Johnson Orthopaedics, Inc., Raynham, MA). After immersion in cool tap water, this material is applied as casts or protective bandages. Casts formed from these products are lightweight, immersible, porous (permeable to water vapor), and fairly strong. Their biggest advantage is that they are virtually radiolucent.⁴

Fiberglass casting tapes consist of a knitted fiberglass fabric impregnated with a polyurethane resin that is activated by water (Delta-Lite Conformable Casting Tape and Delta-Lite “S” Fiberglass Casting Tape, Johnson & Johnson Orthopaedics, Inc.; Synthocast, Kirschner All Orthopedic Appliances, Marlow, OK; Scotchcast II, Orthopedic Products, Surgical Products Division/3M, St. Paul, MN; and Vet Cast and Vet Cast II, Animal Care Products/3M) The water-activated fiberglass casting tapes have met with success in veterinary medicine despite their expense. Differences among the products involve mainly their “handling” ability during application and the final “finish” or smoothness of the cast after it has set. Both these characteristics are primarily influenced by the knitted weave of a product; closely knitted materials generally are more conformable and easier to apply. Casts made from the fiberglass products are strong, lightweight, radiolucent, permeable to water vapor, and immersible in water.

The third type of synthetic casting material is an open-weave cotton fabric coated with high-density thermoplastic resin (Hexcelite, Kirschner All Orthopedic Appliances). A roll is immersed in hot water (65.5°C) for approximately 30 seconds until soft, it is drained of water, and it is applied when comfortable to the touch. The material begins to harden in approximately 3 minutes and achieves rigidity in 10 minutes. Specific areas can be remolded by application of heat with a 1000-watt portable hair dryer until the material is pliable. Thermolabile casting material is permeable to water vapor because of its open weave and does not exhibit an exothermic reaction while curing; it has a rough finish after application.

Bartels and associates evaluated some synthetic casting materials for their tensile strength, fatigue strength, exothermicity (evolution of heat during polymerization), permeability, radiolucency, and cost.⁴ Although statistically significant differences were found for some of the criteria, no one material was best in all categories tested. Other “clinical” studies have revealed similar results.^8,9 They confirm that no one material is best in all areas because the newer synthetic casting materials, although easier to handle, are not as strong as the previous, tackier synthetic cast materials.

Packages of water-activated casting tape should be opened one at a time and used within 2 to 3 minutes because exposure to humidity in the air hardens the tape. Because unused packages can deteriorate on the shelf, sealed, unused rolls should be stored in a refrigerator to retard premature hardening. Most manufacturers date their products and recommend that the rolls of dated cast material be used within 6 months.

Application Technique

Water-activated synthetic casting products should be immersed in cool water (21 to 27°C), because warmer water temperatures greatly decrease setting time, and the heat produced during polymerization can be uncomfortable to the patient during cast application. Immersion in water can vary from 5 to 15 seconds, and the cast rolls should be drained of excess water. Gloves should be worn when handling any of the water- activated materials to protect the hands from any residue, which is difficult to remove. Four to five layers of material should be used, according to manufacturer’s recommendations for weight-bearing casts in small animals.⁴

Techniques for applying synthetic casting materials differ from those usually recommended for plaster casting material. To change directions during application, tucks are made in plaster and thermolabile materials while fiberglass material is twisted. Synthetic materials are molded only in a horizontal motion to ensure lamination. Maximum bonding of the cast layers can be achieved by firmly blotting the exterior of the cast with the open palms in a rolling motion. Molding is achieved by maintaining a desired position for about 1 minute during the last few minutes of the setting period, which varies from 2 to 6 minutes, depending on the temperature of the water for activation. One manufacturer (Vet Cast, Vet Cast II, Animal Care Products/3M) supplies a hand cream to facilitate smoothing and molding of the cast, but water-soluble lubricating jelly (K-Y Lubricating Jelly, Johnson & Johnson Products, Inc., New Brunswick, NJ) can also be used for this purpose. Another manufacturer includes casting gloves that give the polyurethane resin-impregnated fiberglass substrate tack-free working properties (Johnson & Johnson Orthopaedics, Inc.).

Synthetic casts are lighter than their plaster counterparts and, when applied using polypropylene stockinette and polyester padding, they can be immersed in water. Synthetic casts are easier to keep clean because they can be washed with mild soaps, and hydrotherapy for postoperative orthopedic rehabilitation is possible with them. If inadequate drying of the cast occurs and the skin remains wet, irritation and possible skin maceration can occur. Hair dryers can be used to dry wet fiberglass casts.

Long Leg Cylinder Cast

Application Technique

If external coaptation is chosen for fracture repair, the fracture must be reduced before cast placement. Manipulation of the cast after placement causes creases and pressure points in the cast. General anesthesia facilitates fracture alignment and prevents the animal from disrupting reduction while the cast becomes rigid. At least 50% of the fracture ends should be in contact with each other to expect fracture healing, although perfect reduction is the goal for every fracture.¹ In addition, the limb should be reduced in a normal walking position to facilitate early usage of the casted limb and normal limb function after cast removal. The leg should be clipped and aseptically prepared as for surgery in case a closed fracture becomes an open fracture during manipulation. The animal should be placed in lateral recumbency with the affected limb down; this positioning helps to prevent a valgus deformity at the fracture site during cast application.² The following description of application of a long leg cylinder cast to the front leg emphasizes points that can be recommended when using either plaster or synthetic casting materials:

Adhesive tape stirrups are applied to the cranial and caudal surfaces of the foot with the ends of the tape fixed to a tongue-depressor blade to facilitate separation later. The leg is elevated, and the stirrups can be fastened to an intravenous stand or held in an elevated position by an assistant. One or two layers of orthopedic stockinette are rolled up over the entire limb with no wrinkles and are snugly held by an assistant at the proximal end (Figure 64-10). The stockinette should be long enough to extend distally beyond the toes and into the axillary or inguinal region proximally. Synthetic cast padding that repels moisture is wound around the leg from distal to proximal as snugly as possible.
 

Wrapping the padding from cranial to caudal around the medial aspect of the limb helps to prevent supination when wrapping the forelimb.¹⁰ Two layers are usually adequate, although extra padding may be needed at the proximal and distal aspects of the cast. Uniform full-length padding provides the best protection against dermal injury.¹¹ The cast material is rolled around the leg beginning at the distal end and overlapped by half the width of the roll. The material should be applied smoothly using even conforming pressure; smooth application is facilitated by rolling continuously around the limb in a spiral fashion and not raising the roll away from the skin.⁵ Regardless of the casting material used, a cast should be supported with the palms of the hands and not the fingertips because indentations from the fingers may result in pressure sores. If applied properly, four layers of material are usually adequate for the average-size dog. The pads and toenails of the two central toes may be left exposed if there is no weight-bearing on the foot. If the animal is weightbearing on the limb, an aluminum rod walking bar can be applied to the end of the cast to prevent excoriation of toes and excessive wear to the cast.^1,2 Longitudinal splints of cast material can be applied medially and laterally or cranially and caudally to strengthen the cast before the final layer of casting material is applied (Figure 64-11).

After application of the cast and while the material is still moldable, the leg must be positioned properly as described. The stockinette and padding at the ends of the cast and the tape stirrups are reflected over the ends of the cast. These are secured to the proximal and distal aspects of the cast with circular wraps of tape (Figure 64-12).
 

Postapplication Care

For plaster casts, the animal should be hospitalized for at least 24 hours after application to allow for adequate drying. Synthetic materials such as fiberglass can bear weight in as little as 20 minutes, but the animal should be observed closely for at least 12 to 24 hours to be certain that cast application has been correct and is being tolerated well. While the animal is in the hospital, the cast can be covered with a piece of stockinette to prevent soiling before discharge. Care of a cast is similar to care provided for any splint. The cast should be kept dry and as clean as possible. Routine rechecks should be scheduled, and particular care should be taken to educate the owner on cast management. At removal, the cast should be split longitudinally using a cast saw with short bites made perpendicular to the long axis of the cast, rather than sliding the cast saw down the length of the cast. Cutting a cast in this manner helps to reduce chances of damaging the underlying structures. Cuts should be made on either side of the limb, and the two “half-casts” should be removed carefully. Cast spreaders widen the groove made by the cast saw to facilitate cutting the deeper bandage layers with scissors. Windowing of casts should be avoided because of the danger of edematous tissue herniating through the window.^1,12 If the cast loosens, it should be removed and replaced, because immobilization is lost and pressure necrosis occurs as the cast slips and moves.

References

1. DeCamp CE. External coaptation. In: Slatter D, ed. Textbook of small animal surgery. 2nd ed. Philadelphia: WB Saunders, 1993.
2. Nunamaker DM. Methods of closed fixation. In: Newton CD, Nunamaker DM, eds. Textbook of small animal orthopedics. Philadelphia: JB Lippincott, 1985.
3. Marshall PD, Dibble AK, Walters TH, et al. When should a synthetic casting material be used in preference to plaster of Paris? A cost analysis and guidance for casting departments. Injury 1991;23:542-544.
4. Bartels KE, Penwick RC, Freeman LJ, et al. Mechanical testing and evaluation of eight synthetic casting materials. Vet Surg 1985,14:310.
5. Brinker WO, Piermattei DL, Flo GL, eds. Principles of joint surgery. In: Handbook of small animal orthopedics and fracture treatment. Philadelphia: WB Saunders, 1983.
6. Vet Cast Veterinary Casting Tape: Comparative study of commonly used cast materials. St. Paul, MN: Animal Care Products/ 3M, 1984.
7. Lane PL, Lee MM. New synthetic casts: what nurses need to know. Orthop Nurs 1982,1:13.
8. Bowker P, Powell ES. A clinical evaluation of plaster of Paris and eight synthetic fracture splinting materials. Injury 1992; 23:13-20.
9. Wilson DG, Vanderby R. An evaluation of six synthetic casting materials: strength of cylinders in bending. Vet Surg 1995; 24:55-59.
10. Tobias TA. Slings, padded bandages, splinted bandages, and casts. In: Olmstead ML, ed. Small animal orthopedics. St. Louis: CV Mosby, 1995.
11. Swaim SF, Vaughn DM, Spalding PJ, et al. Evaluation of the dermal effects of cast padding in coaptation casts on dogs. Am J Vet Res 1992;53:1266-1272.
12. Hohn RB. Principles and application of plaster casts. Vet Clin North Am 1975;5:291.

Suggested Readings

DeCamp CE. External coaptation. In: Slatter D, ed. Textbook of small animal surgery. 2nd ed. Philadelphia: WB Saunders, 1993.

Leighton RL. Principles of conservative fracture management: splints and casts. Semin Vet Med Surg 1991;6:39-51.

Tobias TA. Slings, padded bandages, splinted bandages, and casts. In: Olmstead ML, ed. Small animal orthopedics. St. Louis: CV Mosby, 1995.