The effect of level of spinal cord injury on shoulder joint kinetics during manual wheelchair propulsion

Objective. The effects of spinal cord injury level on shoulder kinetics during manual wheelchair propulsion were studied. Design. Single session data collection in a laboratory environment. Methods. Male subjects were divided into four groups: low level paraplegia (n=17), high level paraplegia (n=19), C7 tetraplegia (C7, n=16) and C6 tetraplegia (C6, n=17). Measurements were recorded using a six-camera VICON motion analysis system, a strain gauge instrumented wheel, and wheelchair ergometer. Shoulder joint forces and moments were calculated using the inverse dynamics approach. Results. Mean self-selected propulsion velocity was higher in the paraplegic (low PARAPLEGIA=90.7 m/min; high PARAPLEGIA=83.4 m/min) than tetraplegic (C7=66.5 m/min; C6=47.0 m/min) groups. After covarying for velocity, no significant differences in shoulder joint moments were identified. However, superior push force in subjects with tetraplegia (C7=21.4 N; C6=9.3 N) was significantly higher than in those with high paraplegia (7.3 N), after covarying velocity. Conclusions. The superior push force in the tetraplegic groups coupled with weakness of thoraco-humeral depressors increases susceptibility of the subacromial structures to compression.