Axial Pattern Flaps; Clinical Applications

An axial pattern flap is a skin flap containing a single, consistent myocutaneous artery, vein and nerve that supply a specific region of dermal tissue.1,2 As a result, axial pattern flaps have a more (reliable) and robust blood supply as compared to randomly chosen local flaps, which rely on the subdermal plexus alone for their circulation. Axial pattern flaps are used most commonly to facilitate wound closure following a traumatic event or after extensive tumor resection.

Full Thickness Skin Cover

Axial pattern flaps provide a durable full thickness skin cover for skin defects that can be closed primarily without the need for a vascular (well granulated) wound bed or strict postoperative immobilization (which are critical to the success of skin grafts). Since the blood supply is well preserved and the flaps are created from full-thickness skin, the cosmetic appearance of the flaps are considered excellent (they can be expected to closely resemble the donor site skin). The main advantage of axial pattern flaps over randomly chosen subdermal flaps is that they can be made with a narrow base or with no skin connection, thereby allowing considerable flexibility in flap rotation and transfer of skin to more distant areas. In axial pattern flaps, the length of the flap that can be safely created is related to the known length of the axial vessel supplying the flap. Since the blood supply is so reliable, the survival rate of axial pattern flaps is estimated to be about twice that for local random flaps of comparable size. In randomly chosen flaps, the safe length of a flap can only be estimated by the width of skin connected to the flap base. Smaller length to width ratios for random subdermal flaps are safer since there is better chance that the blood supply to the distal portions of the flap is secure. Thus, the use of these local flaps is usually limited to open wounds in the immediate vicinity of the flap base.

Disadvantage
One disadvantage of axial pattern flaps is that they have specific anatomical borders that must be followed to ensure survival of the flap (incorporating the axial vessel in the flap is imperative). When these borders have been damaged or the axial pattern flap landmarks have been altered by patient positioning, a previous surgery, or trauma, the axial vessel may not be located in the described boundaries and the risk of partial flap necrosis is high.

Axial vessels are distributed in many locations throughout the body surface so the application of these flaps is quite broad. There are, however, some body regions that are not readily covered by axial flaps. These include the more distal extremity areas, and the dorsal and ventral midline (in the central areas of the body). The most commonly used axial pattern flaps in small animal surgery are the thoracodorsal and the caudal superficial epigastric. The following list of axial pattern flaps includes the more common regions they are employed for wound closure. [...]