The purpose of this study was to analyze the kinematics of the glenohumeral joint of normal volunteers, patients with cuff tear and traumatic anterior instability during active abduction using open MRI. Ten normal volunteers (23∼39 years old), 9 patients with cuff tear (54∼70 years old), and 6 patients with anterior instability (17∼30 years old) were examined with an open MR system (0.2T Magnetom Open, Siemens). There was 1 incomplete tear, 1 small tear, 3 middle tear, and 4 massive (supraspinatus and infraspinatus) tear. The scans were done at five different active abduction positions (30°, 60°, 90°, 120°, 150°). The translation of the center of the humeral head relative to the center of the glenoid was measured for both the coronal plane and the axial plane in each case. In the normal shoulders, the translation was within 1mm from the center of the glenoid in the coronal plane, and within 2mm anterior from the center of the glenoid in the axial plane. The massive cuff tear shoulders showed superior and posterior translations, while no remarkable translation was observed in supraspinatus tear shoulders. In anterior instability shoulders, inferior translation was observed at 150° abduction, and anterior (n=4) or posterior (n=2) translation was observed in the axial plane. Normal shoulders showed ball-and-socket kinematics. From the results of the analysis of cuff tear shoulders, the anterior and posterior cuff tendons were considered to play an important role in stabilizing the humeral head toward the glenoid. In anterior instability shoulders, translation of the humeral head in the axial plane was observed even during scapular abduction. This analyzing method is useful to evaluate the three-dimensional kinematics of the glenohumeral joint.
