Fluoroscopic evaluation for subtle shoulder instability.

Fifty patients with unilateral shoulder symptoms and a variety of diagnoses were evaluated with stress testing of both shoulders under general anesthesia using fluoroscopic documentation just before surgery. An axillary lateral view of the glenohumeral joint was taken in neutral rotation and 90 degrees of abduction; this was termed "neutral position." Anterior and posterior translational stresses were then applied and spot radiographs taken. Measurements were made and the translation was expressed as a percentage of displacement of the humeral head with respect to the glenoid. The asymptomatic side was used as a control. We determined that up to 14% anterior translation and up to 37% posterior translation is normal. Using these guidelines, attempts were made to confirm or predict the presence of stability or instability. Thirty-one patients were correctly identified as stable; 14 were correctly identified as unstable. Three patients with anterior shoulder pain were classified as unstable and found to have Bankart lesions at surgery. Overall, specificity was 100% and sensitivity was 93%. Using discriminant function analysis, a difference score of 10% between the symptomatic and control shoulder was generated. This was useful in eliminating interobserver variations in the examination for predicting stability or instability. We recommend this examination as a valuable adjunct to confirm the presence and direction of shoulder instability and predict subtle instability patterns in patients with recalcitrant undiagnosed shoulder pain.