Capsular restraints to anterior-posterior motion of the abducted shoulder: A biomechanical study

Twenty-three fresh-frozen cadaver shoulders free of degenerative arthritis or rotator cuff disease were tested biomechanically to quantitate the contribution of specific capsular structures to restricting anterior-posterior translation of the abducted shoulder. With the glenohumeral joint in 90° of abduction on a servohydraulic control testing system, translation was measured in 30° of forward flexion (with regard to the coronal plane of the scapula), 0°, and 30° of extension while a 25 N anterior-posterior load was applied. Measurements were taken both in the intact (vented) shoulder and after selective cutting of different capsuloligamentous structures was performed. In the intact shoulder the largest anterior-posterior translation occurred in 0° of horizontal flexion and extension with regard to the scapular plane, with equal amounts of anterior and posterior translation noted. The primary anterior-posterior stabilizer of the abducted shoulder is the inferior glenohumeral ligament complex. The anterior band is the primary stabilizer in 30° of horizontal extension and at 0° (neutral). The posterior band is the primary stabilizer in 30° of horizontal flexion. This study quantifies for the first time the normal amount of anterior-posterior translation in the intact cadaveric shoulder model. In addition, it demonstrates the relative role of the anterior and posterior band of the inferior glenohumeral ligament complex in stabilizing the glenohumeral joint at 90° of abduction, where most clinical instability of the shoulder occurs.