The use of the impingement test as a predictor of outcome following subacromial decompression for rotator cuff tendinosis

PURPOSE: To evaluate the use of the impingement test as a predictor of outcome following subacromial decompression for patients with rotator cuff tendinosis. TYPE OF STUDY: Observational study. METHODS: An impingement test was administered to each patient immediately before surgery. Patients underwent a subacromial decompression and were assessed postoperatively at 3 and 6 months. The primary outcome measure was the Western Ontario Rotator Cuff Index (WORC). RESULTS: Thirty patients (mean age, 47.0 years; range, 29.4 to 71.2 years) took part in this study. There was no significant correlation between the classic impingement test (Neer's impingement sign before and after subacromial injection of local anesthetic) and the change in WORC score (r = -.174, P =.358). Similar results were obtained for the aggregate impingement test (pain at rest plus Neer's impingement sign plus Hawkins sign plus resisted abduction) before and after subacromial injection of local anesthetic (r = -.208, P =.270). When divided into categories of improvement following the classic impingement test (worse 0%-25%, 26%-50%, 51%-75%, 76%-100% better), there was no significant difference between groups for outcome as indicated by WORC score (P =.203). Results were similar for the aggregate impingement test (P =.271). CONCLUSIONS: The impingement test is a poor tool for predicting the success of subacromial decompression. There are 6 assumptions discussed that must hold true in order for the impingement test to be a useful predictor of outcome following subacromial decompression. If one or more of these assumptions are not met, or are only partially met, the impingement test would be rendered invalid as a predictor of outcome, as this study suggests.