Abstract
Aims: Although the glenohumeral joint is the most mobile articulation of the human body it is known to exhibit ball-and-socket-kinematics. Compression into the glenoid concavity keeps the humeral head centered. The purpose of this study was to determine the effects of joint position on glenohumeral stability through concavity-compression. Methods: Ten cadaver shoulders were tested. The glenoid was mounted horizontally onto a six-component load cell while the humerus was clamped to a vertically unconstrained slide. An x-y-stage translated the load cell with the glenoid underneath the humeral head in eight different directions. Compressive loads of twenty, forty and sixty Newtons were applied. The tests were repeated in 0, 30, 60 and 90 degrees of glenohumeral abduction with and without labrum. Translation distances and the forces resisting translation were recorded and the stability ratio calculated. Results: The average stability ratio was higher in hanging arm position than in glenohumeral abduction. With intact labrum the highest stability ratio was detected in inferior direction (59.8±7.7 percent), without labrum in superior direction (53.3±7.9 percent). In both conditions the anterior direction showed the lowest stability ratio (32.0±4.4 percent; 30.4±4.1 percent). Resection of the labrum resulted in a decrease in stability ratio of 9.6 ±1.7 percent. With increasing compressive load the stability ratio slightly decreased. Conclusions: Anterior shoulder dislocation may be facilitated by the lower stability in glenohumeral abduction and anterior direction. The labrum may not contribute as much as previously assumed to glenohumeral stability. Even moderate compressive forces are sufficient to provide stability through concavity-compression.
Theses abstracts were prepared by Professor Dr. Frantz Langlais. Correspondence should be addressed to him at EFORT Central Office, Freihofstrasse 22, CH-8700 Küsnacht, Switzerland.
