Determinants of the shoulder pain and disability index in patients with subacromial shoulder pain.

OBJECTIVE To examine the influence of determinants on the Shoulder Pain and Disability Index. DESIGN A cross-sectional study. Baseline registrations were applied. PATIENTS Two hundred patients with subacromial shoulder pain lasting at least 3 months. METHODS A questionnaire consisting of possible determinants, 2 independent variables regarding pain and 2 regarding function, and the outcome measurement. Two multiple regression models (one with and one without the independent variables of pain and function) for the Shoulder Pain and Disability Index, the 2 subscales, and the determinants, were performed. RESULTS The included determinants explained 29% of the variance of the Shoulder Pain and Disability Index (25% for pain and 33% for disability subscale) with pain medication, emotional distress, flexion, and the hand-behind-back range accounting for 26%. When pain and function were included, the final model explained 65% of the variance, with gender, education and range of flexion showing significance. CONCLUSION The determinants explained 26% of the variance of the Shoulder Pain and Disability Index, but explained only a minor proportion when pain and function were included. This supports the Shoulder Pain and Disability Index as a shoulder pain and disability questionnaire.