Manual wheelchair pushrim biomechanics and axle position

Objective: The biomechanics of wheelchair propulsion have been linked to up per extremity injury. Specifically, prior studies have correlated increased median nerve dysfunction with increasing propulsion frequency and a higher rate of rise of the resultant, or total, pushrim force. Despite this link, there is little research on the effect of wheelchair setup on propulsion b iomechanics. The objective of this study was to determine the effect of rea r axle position relative to the shoulder on pushrim biomechanics, Design: Case series. Setting: Biomechanics laboratory. Participants: Forty individuals with paraplegia who use manual wheelchairs for mobility. Intervention: Subjects propelled their own wheelchairs on a dynamometer at two different steady-state speeds and going from a dead stop to maximum spe ed, Bilateral biomechanical data were obtained using a force- and moment-se nsing pushrim and a motion analysis system. Main Outcome Measures: Position of the axle relative to the shoulder at res t both horizontal (XPOS) and vertical (YPOS), and pushrim biomechanical var iables including frequency of propulsion, peak and rate of rise of the resu ltant force, planar moment, and push angle. Partial correlation coefficient s between relative axle position and propulsion biomechanics variables were calculated. Results: After controlling for subject characteristics, XPOS was significan tly correlated with the frequency of propulsion (p <.01) and the rate of ri se of the resultant force (p <.05). In addition, both XPOS and YPOS were si gnificantly correlated with the push angle at multiple speeds (p <.05). Conclusion: Specific biomechanical parameters known to correlate with media n nerve injuries were found to be related to axle position relative to the shoulder. Providing wheelchair users with adjustable axle position and then Fitting the user to the wheelchair can improve propulsion biomechanics and likely reduce the risk of injury.