Wrist biomechanics during two speeds of wheelchair propulsion: An analysis using a local coordinate system

Objective: To describe motion, forces, and moments occurring at the wrist in anatomic terms during wheelchair propulsion; to obtain variables that characterize wrist function during propulsion and are statistically stable; and to determine how these variables change with speed. Design: Case series. Setting: Biomechanics laboratory. Participants: Convenience sample of Paralympic athletes ( n = 6) who use manual wheelchairs for mobility and have unimpaired arm function. Intervention: Subjects propelled a standard wheelchair on a dynamometer at 1.3m/sec and 2.2m/sec. Biomechanical data were obtained using a force and moment sensing pushrim and a motion analysis system. Main Outcome Measures: Maximum angles, forces, and moments in a local, wrist coordinate system. Each variable was evaluated for stability using Cronbach's alpha. Measures found to be stable (∝ > .8) at each speed were then compared to look for differences associated with speed. Results: The following measures were stable at both speeds: maximum wrist flexion, ulnar deviation, and radial deviation angles, peak moments acting to cause wrist flexion, extension, and ulnar deviation, peak shear forces acting between the radial and ulnar styloids, and peak axial force acting at the wrist. Of these measures, the following measures differed ( p < .05) between speeds (±SD): maximum radial deviation (1.3m/sec, 25.1° ± 9.0; 2.2m/sec, 21.4° ± 6.9), peak flexion moment (1.3m/sec, 3.4N · m ± 3.0; 2.2m/sec, 5.2N · m ± 3.7), peak extension moment (1.3m/sec, 10.4N · m ± 4.8; 2.2m/sec, 13.6N · m ± 5.1), peak shear acting from the ulnar styloid to the radial styloid (1.3m/sec, 2.3N ± 2.7, 2.2m/sec, 8.3N ± 7.5) and maximum axial force (1.3m/sec, 50.9N ± 18.2; 2.2m/sec, 65.9N ± 27.6). Conclusion: This study found stable parameters that characterize wrist biomechanics during wheelchair propulsion and varied with speed. Ultimately these parameters may provide insight into the cause and prevention of wrist injuries in manual wheelchair users.