The Effect of Glenohumeral Position on the Shoulder after Traumatic Anterior Dislocation

Abstract

Previous cadaveric studies suggest that positioning the shoulder in an externally rotated position reduces displaced Bankart lesions through a coaptation effect. We hypothesized that positioning the glenohumeral joint in an externally rotated position creates contact pressure between the subscapularis and the anterior labrum. Descriptive laboratory study Eight cadaveric shoulders were used. Contact pressure between the subscapularis and labrum was measured in varying glenohumeral positions using a Tekscan pressure monitor. The position of the anterior band of the inferior glenohumeral ligament was also digitized in those positions. All shoulders were tested in the intact condition, following a surgically created Bankart lesion and following anterior shoulder dislocation. These conditions were also verified by measuring glenohumeral translation and joint forces. For all 8 specimens, the contact pressure between the subscapularis and the anterior labrum was negligible with the humerus externally rotated up to 90° at all abduction angles in intact, surgically created Bankart, and dislocated specimens. There were several glenohumeral positions where the anterior band of the inferior glenohumeral ligament strain in the intact specimens was similar to the postdislocation condition, that is, no statistically significant difference between intact and dislocated specimens. These positions included 30° of glenohumeral abduction with external rotation between 0° and 60°, as well as 45° of abduction with external rotation of 0° and 60°. The anterior band of the inferior glenohumeral ligament strain and glenohumeral anterior-posterior translation measurements revealed that the surgically created Bankart lesion does not simulate the conditions after anterior dislocation of the shoulder. External rotation of the shoulder does not create contact pressure between the subscapularis and the anterior labrum before or after anterior dislocation. The efficacy of external rotation immobilization after anterior-inferior shoulder dislocation is not likely to be related to coaptation of the Bankart lesion by the subscapularis.