Effect of coracoacromial ligament resection on glenohumeral stability under active muscle loading in an in vitro model.

Abstract

The purpose of this study was to determine whether or not the coracoacromial ligament (CAL) has a relevant effect in stabilizing the humeral head under active rotator cuff and deltoid loading compared to passive loading conditions without muscular stabilization. Nine human cadaver shoulders were tested in a dynamic shoulder simulator. Forces of the rotator cuff muscles and the middle deltoid muscle were applied using servohydraulic cylinders, while glenohumeral motion was imposed in closed-loop force-control by a sensor-guided robot. Translational movement was measured with the CAL intact and resected under two different testing conditions: (1) simulated physiologic muscle force loading and (2) the passive drawer test, with loads applied in anterior, anterio-inferior, and anterio-superior directions in different glenohumeral positions. The resection of the CAL caused a significant increase in anterior and superior translation during translational testing and muscle force loading. However, the passive testing mode revealed differences in translation from 2.4 to 4.4 mm. The differences were quantitatively minor under muscle loading conditions, ranging from 0.5 to 1.0 mm. CAL resection induces an increased glenohumeral translation under passive loading conditions without muscular stabilization, whereas the effect under rotator cuff and deltoid loading was defined to be quantitatively small. A resection of the CAL should be critically discussed in shoulders with massive rotator cuff tears. In contrast, in muscularly intact shoulders, the release of the CAL evokes a light increase of translation, the clinical relevance of which is questionable.