RESUMO
An experimental model was developed to determine the effects of pressure on skin and muscle in animals. A pressure-time regimen that consistently produced cutaneous ulceration (100 percent) over a bony pressure point was found to produce no ulceration in skin in a location where muscle separated skin and bone. When pressure was applied to skin over a transposed muscle flap and bone, a reduction of the incidence of ulceration (69 percent) was noted, as compared to the corresponding side without a muscle flap between skin and bone (100 percent ulceration). Histologic studies of skin and muscle biopsies demonstrated epidermal breakdown, increased cellularity, and muscle fiber necrosis when cutaneous ulceration occurred. In the animals without ulceration, were normal muscle or a muscle flap was interposed between skin and bone, there were nevertheless significant areas of muscle necrosis in almost every case. Although these data support the supposition that the increased mass of muscle under skin can diffuse pressure and lessen incidence of ulceration, the extremely high incidence of muscle necrosis in response to pressure, despite absence of skin ulceration points to the possibility that muscle is an unsuitable coverage for a pressure-bearing area.