Posture effect on seating interface biomechanics: comparison between two seating cushions.

Abstract

This study aimed at investigating the effects of sitting posture on ischial pressure and pelvic orientation for two types of cushions. Two types of seating devices, Roho and Polyurethane (PU) Foam cushions, six predefined postures, and two subject groups, Normal and Paraplegic, were tested. Ischial pressure and pelvic orientation were monitored. The sequence in which the cushions were tested were randomized, and the postures were tested according to a preplanned sequence. The experiments were carried out in the laboratory of a rehabilitation engineering centre in Hong Kong. Six paraplegic subjects (referred sample) and 8 normal volunteers were tested. At the time of study, no subjects showed any signs of pressure sore or other health problems. It was hypothesized that sitting posture could significantly affect pelvic orientation as well as pressure distribution. It was also hypothesized that cushion selection was a critical factor in compensating the adverse effects of postures on pressure distribution. With the paraplegic group, the maximum ischial pressure recorded on Roho for various postures ranged from 88 mmHg for the Trunk-Bent-Forward (PF) posture to 146 mmHg for the Trunk-Bent-Right (PR) posture, whereas on PU foam cushions, the values ranged from 106 mmHg for the PF posture to 221 mmHg for the PR posture. With the paraplegic subjects sitting with their trunks bent laterally, it was found that the mean pressure difference between the left and right ischial tuberosities was more prominent on the PU foam cushion than on the Roho. Sitting posture can significantly affect pelvic orientation and ischial pressure. This study was also showed that the Roho cushion was significantly more efficient in compensating the adverse effects of sitting posture on pressure distribution.