DYNAMIC STABILITY DURING REPETITIVE AXIAL GLENOHUMERAL ROTATION USING CINE MRI IN HEALTHY ADULTS

Manual testing for dynamic shoulder instability includes noting and shifting of the humeral head, but the corresponding shift of the axis of rotation has been given little attention. The purpose of this study is to clarify translation of the humeral head during active glenohumeral rotation. Magnetic resonance images were taken at 2images/s on 22 shoulders of 11 healthy men. At 150 degrees shoulder elevation, the supine subject internally and externally rotated the humerus repeatedly over 20s. The location over the glenoid of the center of the humeral head (CENHED) projected was studied. During external rotation, projection of CENHED on the glenoid began posterior to the center of the glenoid and migrated to anterior. During internal rotation, this projection was initially positioned above the glenoid center and midway through the motion, shifted inferiorly to nearly the glenoid center. The projection of CENHED did not significantly differ in location over the glenoid at any position along the range of motion during shoulder rotation. Initial values are now available for judging excessive movements of the humeral head on the glenoid fossa during rotation at 150 degrees of abduction in the scapular plane. The method used in this study is amenable to clinical use.