Examination under anesthesia for evaluation of anterior shoulder instability

Thirty patients with unilateral, traumatic recurrent anterior instability were assessed by examination under anesthesia of both shoulders in the anterior, anteroinferior, inferior, posterior, and posteroinferior directions while the examiner controlled the patients' arm rotation. There were significant side-to-side differences in humeral head translation, depending on arm rotation. Humeral head translation was significantly greater in the abnormal shoulder only in the anteroinferior direction with 40 degrees and 80 degrees of external rotation of the arm. Defining an "abnormal" examination as grade 3 translation (translation of the humeral head up onto the glenoid rim) or grade 4 translation (translation of the humeral head over the glenoid rim, that is, dislocated) and translation two grades greater than the contralateral uninjured side, the test sensitivity was 83%, and the test specificity was 100%. Assessing humeral head translation by examination under anesthesia is a useful adjunct to the diagnostic tools for shoulder instability, but the number of tests should be expanded to include the anteroinferior and posteroinferior directions, and the tests should be done with the arm in varying degrees of rotation.