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Pathophysiology
Pathophysiology
Skin, cartilage, and composite grafts are completely removed from their underlying supporting vascular structures and transplanted to a foreign wound bed where revascularization connecting the wound bed to the graft must successfully take place for graft survival. The metabolic requirements of skin grafts are directly related to their thickness; thus STSGs have a lower metabolic demand than FTSGs, which in turn have a lower metabolic demand than composite grafts.
The stages of skin graft healing can be divided into three stages: imbibition, inosculation, and neovascularization. There may be significant overlap between these stages. Imbibition is the first stage of graft survival that occurs during the first 24 to 48 hours of graft placement.4 During this phase, the graft is ischemic, and graft survival is dependent on local plasma exudate of the recipient wound bed which enters the graft by passive diffusion and increases the graft weight by up to 40%.5 Fibrin forms beneath the graft, keeping the graft in contact with the wound bed. The second stage of graft survival, inosculation, begins approximately 48 to 72 hours after graft placement, and is characterized by the growth of new capillaries from the recipient bed that anastomose with the vasculature of the donor graft.6 Because the graft recipient site must be wellvascularized prior to graft placement for this step to occur, graft recipient sites with exposed bone or cartilage where periosteum or perichondrium have been stripped often benefit from delayed grafting to allow granulation tissue to form in the wound bed prior to graft placement.7 The final stage of graft survival, neovascularization, occurs in conjunction with inosculation, with completion 7 to 10 days after graft placement. Neovascularization describes the achievement of capillary ingrowth and anastomosis between the wound bed and graft with re-establishment of lymphatic flow.6โ8
Postsurgical reinnervation of skin grafts has been demonstrated on a molecular level.9 However, clinically significant reinnervation of grafts is modest, with less than a third of patients with skin grafts on the face able to detect light touch 2 years after graft placement.10