A U-shaped skin flap is often caused by compressive forces on skin overlying bone. The flap usually has abraded skin and extends deep with attached subcutaneous tissues. The edges of the flap are usually irregular and fit together with adjacent wound edges, like a jigsaw puzzle. The survival of a rectangular-shaped flap is dependent on the blood supply from vessels that enter the flap at its base. Survival of a flap is more dependent on its length and not the width of the base; wide and narrow-based flaps survive equally if they are of the same length. Other factors that favor survival include the following: (1) the presence of direct cutaneous arteries or veins coursing the longitudinal axis of the flap (axial-pattern flap); (2) location of the flap in the head or neck, where the vascularity is excellent; (3) younger patients and those without diabetes mellitus or arteriosclerosis; (4) location above the knee and not in areas of scar or previous exposure to radiation, which, especially in the elderly, have diminished vascularity; and (5) absence of excessive tension, kinking, pressure, hematoma, or infection, which may interfere with circulation.
The most reliable way to determine tissue viability in a flap is reexamination 24 h after injury, at which time the viability is well demarcated and can be clearly ascertained. For fresh skin wounds, active bleeding from the distal and dermal margins indicates viability. U-, C-, or V-shaped flaps usually heal with a trapdoor or pincushion effect that results in an elevated bulging of the tissues. Various theories to explain this phenomenon are lymphatic and venous obstruction, hypertrophy of the scar, excessive fatty and redundant tissues, beveled wound edges, and contracture of the scar. Because the traumatic wound is susceptible to the development of infection, it is best to reapproximate the edges of a vascularized flap with the least reactive synthetic monofilament suture using interrupted percutaneous sutures.
Approximation of the irregular wound edges is like putting together a jigsaw puzzle ( Fig 37z26). The wound edges of these lacerations often have a beveled edge rather than a perpendicular configuration (Fig 37-27). It can be argued that this beveled edge may have a favorable influence on healing by providing a large interface between the divided edges, thereby enhancing repair. Consequently, repair of the beveled edges is advocated rather than revising the edges to create perpendicular edges. Suturing beveled edges may be time-consuming because the needle must be passed separately through one edge before it is passed through the other to ensure that the suture passes through the same depth on each side of the wound to align equivalent layers. This time-consuming maneuver is worthwhile because it prevents malapposition of the wound edges and an unattractive scar deformity.
FIG. 37-26. A. V-shaped laceration with irregular wound edges. B. An interrupted percutaneous suture approximates the midportion of the wound. C. Two additional percutaneous sutures are used to approximate the lateral sides of the wound. D. Additional percutaneous sutures are positioned between the previously placed percutaneous sutures. E. The interrupted percutaneous sutures allow the wound to be reconstructed like a jigsaw puzzle.
FIG. 37-27. Closure of beveled edges requires careful approximation of the wound edges. This is facilitated by removing the needle from the needle holder after passage through one side, regrasping the needle, and passing it through the opposite side.
When a portion of the flap is devascularized, this segment should be excised. Ihe excised flap should then be defatted, converting the flap into a skin graft that is applied to the defect and secured by a tie-over bolus dressing. After the skin graft heals without infection, the patient should be referred to a plastic surgeon for follow-up evaluation. Six months after wound closure, the plastic surgeon can correct the trapdoor deformity by performing Z- and W-plasties accompanied by peripheral undermining of the wound. For small trapdoor deformities, simple excision of the deformity resulting in a lenticular defect that can be primarily closed is an excellent alternative.
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