ANTERIOR GLENOHUMERAL STABILIZATION FACTORS - PROGRESSIVE EFFECTS IN A BIOMECHANICAL MODEL

The aim of this study was to evaluate the anterior stabilizing factors of the glenohumeral joint over a range of translations. The stabilize rs examined included the capsular ligaments, the coracohumeral ligamen t, the rotator cuff muscles, and the long head of the biceps. Simulate d muscle forces were applied to eight shoulder specimens to produce 90 degrees of total elevation of the arm in the scapular plane. Stabilit y, defined as the force required to reach a specified subluxation. the n was evaluated under varying configurations of capsule cuts, humeral rotation, and muscular loads. The overall force-displacement relations hip of the subluxation was found to increase exponentially in external rotation to 239 N at 10 mm of displacement and to level off in neutra l rotation to 172 N at 10 mm of displacement. Among the muscles, the b iceps was the most important stabilizer in neutral rotation, providing more than 30 N of stabilization: the subscapularis provided the great est degree of stabilization in external rotation, increasing to approx imately 20 N. The subscapularis and supraspinatus were the most consis tently important stabilizers in both types of rotation. In external ro tation, the superior, middle, and inferior glenohumeral ligaments were the most effective ligamentous stabilizers, and all provided progress ively more stabilization as higher displacements were reached. The sta bility provided by some of the ligaments reached nearly 50 N at 10 mm of displacement.