M A Baldwin

Wheelchair pushrim kinetics: Body weight and median nerve function

OBJECTIVES Individuals who use manual wheelchairs are at high risk for median nerve injury and subsequent carpal tunnel syndrome (CTS). To gain a better understanding of the mechanism behind CTS in manual wheelchair users, this study examined the relation between (1) pushrim biomechanics and function of the median nerve, (2) pushrim biomechanics and subject characteristics, 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 who 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 force- and moment-sensing pushrim and a motion analysis system. Bilateral nerve conduction studies focusing on the median nerve were also completed. MAIN OUTCOME MEASURES Pearsons correlation coefficients between subject characteristics, median nerve conduction studies, and propulsion biomechanics; a regression model of nerve conduction studies incorporating subject characteristics 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 applied to the pushrim (r = .59, p < .001). Height, weight, and weight-normalized pushrim forces were successfully incorporated into a linear regression model predicting median sensory amplitude (r = .63, p < .05) and mean median 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 biomechanics were also related to median nerve function. Through weight loss and changes in pushrim biomechanics, it may be possible to prevent median nerve injury in manual wheelchair users.

Manual wheelchair pushrim biomechanics and axle position

OBJECTIVE The biomechanics of wheelchair propulsion have been linked to upper 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 biomechanics. The objective of this study was to determine the effect of rear 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 speed. Bilateral biomechanical data were obtained using a force- and moment-sensing pushrim and a motion analysis system. MAIN OUTCOME MEASURES Position of the axle relative to the shoulder at rest both horizontal (XPOS) and vertical (YPOS), and pushrim biomechanical variables including frequency of propulsion, peak and rate of rise of the resultant force, planar moment, and push angle. Partial correlation coefficients between relative axle position and propulsion biomechanics variables were calculated. RESULTS After controlling for subject characteristics, XPOS was significantly correlated with the frequency of propulsion (p < .01) and the rate of rise of the resultant force (p < .05). In addition, both XPOS and YPOS were significantly correlated with the push angle at multiple speeds (p < .05). CONCLUSION Specific biomechanical parameters known to correlate with median 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.

Wrist kinematics and indicators of carpal tunnel syndrome during manual wheelchair propulsion

This study compared wrist kinematics during manual wheelchair propulsion (MWP) for 22 experienced Manual Wheelchair Users (MWU) with and without evidence of median mononeuropathy (MMN), an indicator of CTS. Thirteen (13) MWUs tested positive for MMN. Analysis found significantly higher peak wrist flexion for MWU who demonstrated CTS via the nerve conduction study. It may be prudent to instruct MWUs to avoid extremes of wrist extension.

EMG activity of wrist muscles during wheelchair propulsion

Wheelchair users are at an increased risk for developing carpal tunnel syndrome (CTS). The objective of this study was to use electromyography (EMG) to describe wrist flexor activity (WFA) during wheelchair propulsion. EMG data on 3 flexor muscles for one subject were collected while he propelled at a constant speed of 0.9 m/s (2 mph). The flexor carpi radialis was the most active flexor muscle during the push phase with peak and average EMG at 51% and 33% of its maximum isometric contraction value.

Comparison of propulsion kinetics and forearm EMG between two wheelchair pushrim designs

The electromyographic (EMG) activity of forearm muscles and pushrim forces were compared between a standard and an ergonomic wheelchair pushrim for a group of non-impaired subjects propelling at two and four miles per hour. The maximum EMG signals were not statistically different for any of the muscles between rims while significantly higher peak tangential, radial, and resultant forces were found for the ergonomic pushrims.

Kinematic model of wrist via marker placement during manual wheelchair propulsion

Due to the dynamic nature of MWP, motion analysis via markers placed on bony prominences provides the best approximation of the three dimensional trajectory of the segments of the upper extremity. Previous models which use motion analysis markers have been described in the literature, but these models have not corrected for positioning of the hand in a non-neutral position. The current model provides a standard method for determining the three ranges of motion commonly attributed to the wrist: flexion/extension, radial/ulnar deviation, and pronation/supination. These quantities are calculated via a local coordinate system based at the wrist as described by Shimada (1997), but applies a correction factor to account for non-neutral hand position during calibration.