Measurement and redistribution of excessive pressures during wheelchair sitting.

The ischial tuberosities, the sacral coccygeal area, and the greater and lesser trochanters and intertrochanteric crests receive excessive pressures when an individual is in the sitting position. Prolonged sitting by patients with insensitive skin and physical disability can cause pressure sores. Pressures below 20 to 30 mmHg are required to prevent capillary occlusion. Pressures are measured with a transducer system as the patient sits in his natural sitting posture in his wheelchair. A seat cushion is then "customized," which will redistribute excessive pressures. The most common cushion used is made of 3-in or 4-in high-density polyurethane foam. This material is easily modified when making ischial tuberosity cutouts and constructing a preischial bar. Because there is no single safe sitting pressure, each patient must be provided with a cushion support system that best reduces his excessive pressures. Although a properly fitted cushion can redistribute pressure, it can never substitute for relief of weight-bearing areas routinely carried out several times each hour.