In vivo (CT scan) comparison of vertical shear in human tissue caused by various support surfaces.

Shear stress and shear strain of human tissue were calculated in vivo using measurements derived from pelvic CT scans of three subjects lying upon three depths of foam mattress overlays and an air mattress overlay commonly used in the prevention of pressure ulcers. The air mattress overlay plus three-inch foam had the lowest degree of tissue shear when compared with the foam overlays both quantitatively and qualitatively. In addition, it was found that the contouring air mattress overlay plus three-inch foam provided the greatest area of contact between surface support and subject when compared to the foam overlays, resulting in a greater distribution of applied load and ultimately decreasing tissue shear.