The prevalence of shoulder joint pathology is notably higher in individuals with spinal cord injury (SCI) than in the able-bodied population for any age group. Chronic shoulder pain after SCI has been associated with the repetitive weight bearing of wheelchair propulsion (WCP), but a causal relationship has not been established. Preliminary evidence indicates that individuals who develop shoulder joint pain have a less efficient pattern of WCP even years prior to the onset of pain than in those who remain pain-free. This project will determine whether this pattern is found in a larger prospective sample. Additionally, an imbalance in the strength of the rotator cuff muscles has been documented in individuals with shoulder pain after SCI. It is unclear if the reduced strength in the rotator cuff is a precursor of shoulder pathology or a secondary effect. We will relate the damaging forces at the shoulder to the pattern of motion and force application to the push rim. The long-term goal will be to develop biomechanical guidelines for optimum, less stressful shoulder function. Subjects will have complete paraplegia, be between 2 and 15 years post SCI, and free of shoulder pain measured on the Wheelchair Users Shoulder Pain Index (WUSPI). Predictor variables will be measured at entry into the study, at 18 months and 3 years. A biomechanical analysis of WCP performed in the laboratory setting will document subjects'pattern of upper extremity motion, shoulder joint reaction forces and force application on the push rim during free, fast, and incline propulsion. Shoulder strength will be documented by recording maximal isometric torques at the shoulder. An odometer attached to the subject's wheelchair will document the daily distance and average speed of WCP in the home and community. Readings from the odometer will be taken monthly over the 3 year follow-up period. The primary outcome will be change in the Wheelchair Users Shoulder Pain Index. The combination of factors that determine the increase of shoulder joint pain will be identified. Using logistic regression analysis we will determine the odds ratios for the vertical shoulder joint reaction force during WCP, shoulder muscle strength (normalized by body weight), age/time since SCI, level of SCI, and quantitated wheelchair activity for the development of shoulder joint pain over a 3 year period in a cohort of subjects. MANOVA will be employed to compare the biomechanical parameters of WCP for the shoulder pain and pain-free groups.
