BIOMECHANICAL EVALUATION OF A SIMULATED BANKART LESION

The purpose of this study was to determine the effect of sectioning of the anterior part of the inferior glenohumeral ligament (a simulated Bankart lesion) on load-induced multidirectional glenohumeral motion. Nine fresh, intact cadaveric shoulders were tested on a special apparatus that constrained three rotations but allowed simultaneous measurement of anterior-posterior, superior-inferior, and medial-lateral translation. Coupled anterior-posterior and superior-posterior translations were recorded while anterior, posterior, superior, and inferior forces of fifty newtons were applied sequentially. Testing was done in three positions of humeral elevation in the scapular plane, in three positions of humeral rotation, and with an externally applied joint-compression load of twenty-two newtons. A liquid-metal strain-gauge was placed on the posterior band of the inferior glenohumeral ligament to assess concomitant posterior capsular strain during the various test conditions. All shoulders were tested intact and again after the inferior glenohumeral ligament and the labrum had been detached from the glenoid from just superior to the anterior band of the inferior glenohumeral ligament to a point just posterior to the infraglenoid tubercle. The simulated Bankart lesion resulted in selected increases in anterior translation at all positions of elevation, in posterior translation at 90 degrees of elevation, and in inferior translation at all positions of elevation. However, these increases were very small; the maximum mean increase in translation seen over-all was only 3.4 millimeters, which occurred during inferior translation at 45 degrees of elevation. The coupled anterior-posterior and superior-inferior motion resulting from the application of either the superior-inferior or the anterior-posterior force, respectively was not affected by the simulated Bankart lesion. Altered patterns of tension were demonstrated in the posterior aspect of the capsule after creation of the Bankart lesion. CLINICAL RELEVANCE: injury to the anterior part of the inferior ligament at the level of the glenoid does not appear to be solely responsible for the increased anterior glenohumeral translation that is necessary to produce an anterior dislocation of the shoulder. The present study demonstrates that the detachment of the anterior half of the inferior glenohumeral ligament from the glenoid results in only a slight increase in anterior translation. This indicates that permanent stretching or elongation of the inferior glenohumeral ligament may also be necessary to produce anterior glenohumeral dislocation.