Effects of anteroinferior capsulolabral incision and resection on glenohumeral joint reaction force.

Successful outcome of a Bankart procedure depends on knowledge of the effects of capsulolabral lesions on joint biomechanics. The joint reaction force, through "concavity compression," is integral to glenohumeral stability. In this study, we applied loads to the tendons of the rotator cuff and deltoid (anterior and middle portions) of five cadaver upper limbs. The joint reaction force was measured with a 6 degrees of freedom load cell for the intact condition and each of two test conditions: (1) incision and (2) partial resection of the anteroinferior capsulolabrum. We used analysis of variance to compare joint reaction forces resolved into that which is directed perpendicular (compression force), anterior, and superior to the glenoid. Compression force for the two different capsulolabral lesions of the glenohumeral joint was the same, 133 N +/- 13 N, a small 12% decrease compared to the intact condition (151 N +/- 13 N). This difference was not statistically significant. Results were similar for the components of the joint reaction force directed anterior and superior. Joint reaction force was not meaningfully altered after anteroinferior capsulolabral lesions were simulated. Because glenohumeral joint stability involves complex interplay of static and dynamic restraints, additional shoulder injuries may be necessary for the joint reaction force to be abnormal.