Pelvic movement and interface pressure distribution during manual wheelchair propulsion

OBJECTIVE: To investigate the movement of the ischial tuberosities and the redistribution of interface pressure during manual wheelchair propulsion. DESIGN: Measurement of ischial tuberosity positions and comparison with corresponding position of the zones of peak pressure by using independent samples t tests. Analysis of variance was used to compare peak and average pressures under static and dynamic conditions. SETTING: Human locomotion laboratory. PARTICIPANTS: Ten subjects with spinal cord injury (SCI) and 10 individuals with no disabilities. INTERVENTIONS: Manual wheelchair propulsion on a stationary wheelchair ergometer at the subject's maximum propulsion speed. MAIN OUTCOME MEASURES: Seat interface pressure and the 3-dimensional position of the pelvis were measured with a pressure mat and an optical motion analysis system. RESULTS: During wheelchair sprinting, the ischia were located at 19.2+/-11.7 mm behind the corresponding peak pressure locations. The anteroposterior rocking of the pelvis was 11.2 degrees and 5.2 degrees for the normal and SCI group, respectively. The average interface pressure over the ischial tuberosity area was lower under dynamic conditions. It was also observed in the SCI group that there was a concentration of high-pressure gradients around the peak pressure areas of the buttock during dynamic propulsion. CONCLUSION: Peak pressure locations did not concur exactly with the ischial tuberosities during propulsion. The movements of the ischial bone and the cyclic loading imposed on the tissue underneath the ischial tuberosities during dynamic conditions may have implications for the etiology of decubitus ulcers.