Ligamentous restraints to external rotation of the humerus in the late-cocking phase of throwing - A cadaveric biomechanical investigation

The late-cocking phase of throwing is characterized by extreme external rot ation of the abducted arm; repeated stress in this position is a potential source of glenohumeral joint laxity. To determine the ligamentous restraint s for external rotation in this position, 20 cadaver shoulders (mean age, 6 5 +/- 16 years) were dissected, leaving the rotator cuff tendons, coracoacr omial ligament, glenohumeral capsule and ligaments, and coracohumeral ligam ent intact. The combined superior and middle glenohumeral ligaments, anteri or band of the inferior glenohumeral ligament, and the entire inferior glen ohumeral ligament were marked with sutures during arthroscopy. Specimens we re mounted in a testing apparatus to simulate the late-cocking position. Fo rces of 22 N were applied to each of the rotator cuff tendons. An external rotation torque (0.06 N.m/sec to a peak of 3.4 N.m) was applied to the hume rus of each specimen with the capsule intact and again after a single rando mly chosen ligament was cut (N = 5 in each group). Cutting the entire infer ior glenohumeral ligament resulted in the greatest increase in external rot ation (10.2 degrees +/- 4.9 degrees). This was not significantly different from sectioning the coracohumeral ligament (8.6 degrees +/- 7.3 degrees). T he anterior band of the inferior glenohumeral ligament (2.7 degrees +/- 1.5 degrees) and the superior and middle glenohumeral ligaments (0.7 degrees /- 0.3 degrees) were significantly less important in limiting external rota tion.