The interactions between hand pattern, shoulder pain and upper extremity demand in manual wheelchair users
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Manual wheelchair users rely on their upper limbs for independent mobility, which requires frequent loading of their upper extremities. This loading often results in shoulder pain and injuries, which leads to decreased independence and quality of life. The overall goal of this research was to understand how the recovery hand pattern used by manual wheelchair users influences shoulder pain development and upper extremity demand through a series of studies using experimental and simulation methods. Previous research has identified shoulder adductor weakness as a predictor of shoulder pain development in manual wheelchair users. Therefore, an experimental study determined whether the hand pattern used during fast wheelchair propulsion was correlated with shoulder pain development and shoulder adductor strength. We found that over-rim patterns were not correlated with any pain groups. However, more over-rim patterns were weakly correlated with lower adductor strength, but the variability in this correlation was high. Thus, changing hand patterns alone may not be sufficient to prevent or mitigate shoulder pain. In a second study, shoulder joint contact forces were compared between hand patterns and within each pattern when different shoulder muscles were weakened using modeling and simulation techniques. Single-loop and semi-circular patterns required the highest and lowest joint contact force, respectively. Weakened internal rotators in all patterns and weakened adductors in single-loop and double-loop patterns induced the highest joint loading increases compared to non-weakened conditions. This suggests that shoulder joint loading is lowest when using a semi-circular pattern with and without shoulder muscle weakness, and therefore is less likely to result in shoulder injuries. A final modeling study quantified different measures of demand (muscle stress and power, metabolic cost and shoulder joint loading) for different hand patterns on a continuum. Patterns that were more under-rim improved multiple demand measures (muscle stress, total muscle power and peak joint contact force), but only weak trends were present in other measures. Thus, using under-rim patterns reduces these demand measures and consequently the risk of injury. Together, these studies provide additional insight into how manual wheelchair users can alter their recovery hand pattern for the prevention of shoulder pain and injuries.