Shoulder computed arthrotomography: role of internal and external rotation.

Computed arthrotomography of the shoulder is the best investigation for instability of the glenohumeral joint. The purpose of this paper is to evaluate the role of internal rotation and external rotation in detecting glenoid and capsular lesions. From October 1989 to December 1991, 74 double-contrast CT arthrograms of the shoulder were performed with both internal and external rotation. Most of these patients were referred for instability problems or shoulder pain of vague origin. Of the 49 abnormalities of the anterior portion of glenoid labrum, 44 (89.8%) were identified on the scans with internal rotation; however, 5 (10.2%) was seen only in external rotation view. Most of the anterior capsular abnormalities occurred on the internal rotation. Only one of 74 examination was evidenced solely on external rotation. There were relatively few posterior labral or capsule abnormalities. Of the five, two were seen solely on external rotation. The results suggest that internal rotation scans detect most of the lesions; however, with the help of external rotation view, 10% increase in diagnostic yield can be expected for anterior labral abnormalities. Although few posterior labral or capsule lesions occur, external rotation examination does play an important role in this respect.