Internal rotation resistance strength test: a new diagnostic test to differentiate intra-articular pathology from outlet (Neer) impingement syndrome in the shoulder.

This prospective study introduces a new sign to differentiate between outlet impingement and non-outlet (intra-articular) causes of shoulder pain in patients with positive impingement sign: the internal rotation resistance strength test (IRRST). It was hypothesized that positive test results are predictive of non-outlet impingement, whereas negative test results confirm outlet impingement. A prospective comparison between IRRST and arthroscopic findings of 115 consecutive patients showed the test to be highly accurate in differentiating between these two diagnoses (positive predictive value 88%, negative predictive value 96%, sensitivity 88%, specificity 96%, and accuracy 94.5%). The IRRST, in conjunction with impingement and apprehension signs, adds to our armamentarium of tests that distinguish between subacromial outlet impingement and intra-articular forms of pathology.