Ultrasound mapping of the buttock-cushion interface contour.

For patients susceptible to decubitus ulcers, wheelchair cushions and other body support surfaces must be prescribed with a view to providing a uniform distribution of buttock-cushion interface pressures. The capacity to distribute pressure uniformly at the support interface depends on the shape of the bony prominences, and the amount and mechanical compliance of the overlying soft tissue: an indication of this capability may be given by the indentation contour of the buttock-cushion interface. Using normal subjects, we devised a method for measuring this contour using ultrasonic dimension gauging techniques. Because the technique can describe the geometry of soft tissues deformed under load, it could make an important contribution to successful employment of analytical modeling to predict internal tissue stresses during sitting.