Skills Laboratory: Reconstructive surgery techniques, Part 4: Full-thickness mesh skin grafts
A full-thickness mesh graft is a sheet of skin that includes only the epidermis and the entire dermis and is fenestrated to allow for expansion and drainage. All subcutaneous tissue is removed from the graft. Full-thickness mesh grafts are indicated to cover defects when skin is not available for local flaps or for moving local tissue or when excessive tension would be created by using such wound closure techniques as placing presutures or an adjustable horizontal mattress suture or making multiple punctate relaxing incisions (Figure 1). They are most commonly used to close mid- and distal-limb defects. Full-thickness mesh grafts are indicated for excision sites or for fresh wounds with well-vascularized tissue—enough vascularization to produce granulation tissue—or a bed of healthy granulation tissue that has started to epithelialize.
Figure 1. Skin stretching or relaxing procedures will be ineffective for wound closure.
The day before grafting, administer a neuroleptanalgesic and use a No. 10 scalpel blade to scrape the wound’s surface of granulation tissue to remove any coagulum on the wound surface. Bandage the wound with mesh gauze coated with gentamicin sulfate antibiotic ointment (not cream). Apply an absorbent secondary wrap and a tertiary adhesive wrap.1 Removing coagulum, applying an antibiotic, and bandaging may help reduce bacterial flora on the wound surface, helping ensure that infection will not interfere with graft healing.1
Dogs and cats have an abundance of loose, well-haired skin on the lower craniolateral thoracic area. This area is ideal for obtaining skin for a graft, with sufficient skin to close the defect after graft harvest. Before surgery, tent the skin on the proposed donor site to ensure that sufficient skin is available for obtaining the graft and for wound closure after graft removal. If closure of the donor site causes tension, you may place walking sutures to relieve the tension.
While adequately restraining the patient, change the bandage daily for the first seven days.1,2 A graft may appear quite ischemic for the first two days after placement. Later, it may appear cyanotic and edematous. As the graft heals, it becomes less edematous and cyanotic and the color changes from deep red to pink. As granulation tissue grows up into the mesh holes, drainage decreases. Bandages can be changed less often as drainage decreases: every other day, then every third or fourth day, depending on clinical judgment. By 21 days, bandaging is usually discontinued. Sutures are generally removed seven to 10 days after grafting.
In people, about three weeks after grafting, reinnervation with a pins-and-needles sensation reportedly occurs. It is speculated that this sensation may occur in dogs as well and may be manifested by excessive licking and chewing at the graft after the bandage is removed at three weeks. If an owner reports that a dog is excessively licking a graft after bandage removal at three weeks, I recommend continued bandaging for another week. During the postoperative healing period, restrict exercise—the patient should receive cage rest with periodic excursions during the day for elimination. Limited exercise is particularly important early in the healing process to allow vascular and connective tissue attachments to become established.
Occasionally, only partial-thickness healing occurs, whereby the deeper part of the dermis revascularizes and heals but the epidermis and superficial dermis are lost. When this occurs, débride the nonviable superficial slough during bandage changes if it is loosely attached to the graft. If slough has not started to detach, delay débriding until the separation has started. Delaying débridement avoids damage to the underlying graft dermis. The healed dermis will epithelialize and provide a wound covering; however, it will have a sparse hair covering due to follicle loss. If a graft is completely lost, treat the wound as an open wound, and allow it to heal by contraction and epithelialization. If healing is insufficient, perform a second graft.
ADVANTAGES AND DISADVANTAGES
A disadvantage of mesh grafts is their poor cosmetic appearance early in the healing process; however, as healing progresses, the slits become less noticeable as they get smaller and hair regrows on the graft. Growth of hair on a graft is variable and unpredictable. Some grafts have full regrowth of hair while others will have sparse hair regrowth, especially with partial-thickness graft healing.
Steven F. Swaim, DVM, MS