Effect of seat cushion on dynamic stability in sitting during a reaching task in wheelchair users with paraplegia

Objectives: To examine the effects of seat cushions on dynamic stability in sitting during a controlled reaching task by wheelchair users with paraplegia. Design: A randomized, controlled test. Setting: Rehabilitation center. Participants: Nine wheelchair users with paraplegia. Interventions: Three types of cushions-an air flotation, a generic contoured, and a Bat polyurethane foam-were tested during a controlled reaching task in ipsilateral and contralateral directions, at 45 degrees from the sagittal plane in the anterolateral direction. Center of pressure (COP) coordinates were monitored by using a pressure measurement system as well as a force platform under slat. Main Outcome Measures: Trajectory of COP, maximal distance covered by COP, maximal velocity of COP; and the index of asymmetry between right and left maximal pressure under ischial tuberosities. Results: The genetic contoured cushion allowed the COP to cover significantly (p < .02) a larger distance (81 +/- 28mm) when compared with the air flotation (63 +/- 25mm) or the Bat foam (61 +/- 29mm) cushions. The COP velocity was significant (p < .05) for the generic contoured cushion (.14 +/- 0.5m/s) versus the air floatation (.10 +/- .04m/s) or the Bat-foam (.10 +/- .03m/s) cushions. The index of asymmetry was higher for the generic contoured and the Bat foam cushions. During reaching, maximal pressure under ipsilateral ischial tuberosity was significantly higher for the flat foam (275 +/- 70mmHg) and the generic contoured (235 +/- 81mmHg) cushions, when compared with the air flotation cushion (143 +/- 51mmHg). Conclusion: Seat cushions can significantly affect sitting balance during reaching tasks. This study provided an objective method to assess the dynamic stability of wheelchair users when they perform activities of daily living requiring reaching. These findings have implications for wheelchair seating recommendations, especially seat cushion selection.