Wheelchair Pushrim kinetics: Body weight and median nerve function

Objectives: Individuals who use manual wheelchairs are at high risk for med ian nerve injury and subsequent carpal tunnel syndrome (CTS), To gain a bet ter understanding of the mechanism behind CTS in manual wheelchair users, t his study examined the relation between (1) pushrim biomechanics and functi on of the median nerve, (2) pushrim biomechanics and subject characteristic s, and (3) median nerve function and subject characteristics. Design: Case series. Setting: Biomechanics laboratory and an electromyography laboratory. Participants: Thirty-four randomly recruited individuals with paraplegia wh o use a manual wheelchair for mobility. Intervention: Subjects propelled their own wheelchair on a dynamometer at 0 .9m/sec and 1.8m/sec. Bilateral biomechanical data were obtained using a fo rce- and moment-sensing pushrim and a motion analysis system, Bilateral ner ve conduction studies focusing on the median nerve were also completed. Main Outcome Measures: Pearson's correlation coefficients between subject c haracteristics, median nerve conduction studies, and propulsion biomechanic s; a regression model of nerve conduction studies incorporating subject cha racteristics and pushrim biomechanics. Results: Subject weight was significantly related to median nerve latency ( r = .36, p = .03) and median sensory amplitude (r = -.43, p = .01). Height was also significantly related to median sensory amplitude (r = -.58, p = . 01). Subject weight was significantly related to the peak resultant force a pplied to the pushrim (r = .59, p < .001). Height, weight, and weight-norma lized pushrim forces were successfully incorporated into a linear regressio n model predicting median sensory amplitude (r = .63,p < .05) and mean medi an latency (r = .54, p < .05), Conclusion: This study found subject weight to be related to pushrim forces and median nerve function. Independent of subject weight, pushrim biomecha nics were also related to median nerve function. Through weight loss and ch anges in pushrim biomechanics, it may be possible to prevent median nerve i njury in manual wheelchair users. (C) 1999 by the American Congress of Reha bilitation Medicine and the American Academy of Physical Medicine and Rehab ilitation.