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 tra nslation after release of the coracoacromial ligament. Six fresh, frozen un paired glenohumeral joints were tested in a neutral position and at 30 degr ees internal and 30 degrees external rotation of the humerus at 0 degrees 3 0 degrees and 60 degrees of abduction on a custom glenohumeral joint transl ation testing apparatus. A joint compression load of 20 N was simulated; th en 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 wit h a P value of .05 as the level of significance. At 0 degrees and 30 degree s of abduction, release of the coracoacromial ligament resulted in a signif icant increase in glenohumeral joint translations, in both the anterior and inferior directions. In addition, the differences in translation between b efore and after the release of the coracoacromial ligament decreased in all directions as glenohumeral abduction increased, and they were not signific ant 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 restra int of the glenohumeral joint. It provides a suspension Function and may re strain anterior and inferior translations through an interaction With the c oracohumeral ligament. Although this is a biomechanical study without simul ation of the shoulder muscles, it indicates that the coracoacromial ligamen t contributes to glenohumeral stability. Caution should be exercised in the release of the coracoacromial ligament in those with rotator cuff pain ass ociated with glenohumeral instability.