Shoulder Strength and Physical Activity Predictors of Shoulder Pain in People With Paraplegia From Spinal Injury: Prospective Cohort Study

BACKGROUND: Shoulder joint pain is a frequent secondary complaint for people following spinal cord injury (SCI). OBJECTIVE: The purpose of this study was to determine predictors of shoulder joint pain in people with paraplegia. METHODS/DESIGN: A 3-year longitudinal study was conducted. Participants were people with paraplegia who used a manual wheelchair for at least 50% of their mobility and were asymptomatic for shoulder pain at study entry. Participants were classified as having developed shoulder pain if they experienced an increase of ≥10 points on the Wheelchair User's Shoulder Pain Index in the 3-year follow-up period. Measurements of maximal isometric shoulder torques were collected at study entry (baseline), 18 months, and 3 years. Daily activity was measured using a wheelchair odometer, and self-reported daily transfer and raise frequency data were collected by telephone every 6 weeks. RESULTS: Two hundred twenty-three participants were enrolled in the study; 39.8% developed shoulder pain over the 3-year follow-up period. Demographic variables and higher activity levels were not associated with shoulder pain onset. Baseline maximal isometric torque (normalized by body weight) in all shoulder muscle groups was 10% to 15% lower in participants who developed shoulder pain compared with those who remained pain-free. Lower shoulder adduction torque was a significant predictor of shoulder pain development (log-likelihood test=11.38), but the model explained only 7.5% of shoulder pain onset and consequently is of limited clinical utility. LIMITATIONS: Time since SCI varied widely among participants, and transfer and raise activity was measured by participant recall. CONCLUSIONS: Participants who developed shoulder pain had decreased muscle strength, particularly in the shoulder adductors, and lower levels of physical activity prior to the onset of shoulder pain. Neither factor was a strong predictor of shoulder pain onset.