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.
The IRRST is performed in the standing position with the examiner positioned behind the patient. The arm is positioned in 90° of abduction in the coronal plane and approximately 80° of external rotation. A manual isometric muscle test is performed for external rotation and then compared with one for internal rotation in the same position
If a patient with a positive impingement sign has good strength in external rotation in this position and apparent weakness in internal rotation, the IRRST result is considered positive. Because this is a test of relative weakness in a pathologic shoulder, strength is not compared with the contralateral normal arm.