Release of the coracoacromial ligament can lead to glenohumeral laxity: a biomechanical study.

The purpose of this study was to determine change in glenohumeral joint translation after release of the coracoacromial ligament. Six fresh, frozen unpaired glenohumeral joints were tested in a neutral position and at 30 degrees internal and 30 degrees external rotation of the humerus at 0 degrees, 30 degrees, and 60 degrees of abduction on a custom glenohumeral joint translation testing apparatus. A joint compression load of 20 N was simulated; then a 15-N load was applied to the humerus in anterior, posterior, superior, and inferior directions, and translations on the glenoid were measured with an electromagnetic tracking device. The tests were then repeated after a 1.5-cm section of the coracoacromial ligament was released from the acromion. A multivariate analysis of variance was used for statistical analyses with a P value of.05 as the level of significance. At 0 degrees and 30 degrees of abduction, release of the coracoacromial ligament resulted in a significant increase in glenohumeral joint translations, in both the anterior and inferior directions. In addition, the differences in translation between before and after the release of the coracoacromial ligament decreased in all directions as glenohumeral abduction increased, and they were not significant at 60 degrees of abduction in any of the rotations. The results of this study suggest that the coracoacromial ligament has a role in static restraint of the glenohumeral joint. It provides a suspension function and may restrain anterior and inferior translations through an interaction with the coracohumeral ligament. Although this is a biomechanical study without simulation of the shoulder muscles, it indicates that the coracoacromial ligament contributes to glenohumeral stability. Caution should be exercised in the release of the coracoacromial ligament in those with rotator cuff pain associated with glenohumeral instability.