The role of the acromioclavicular ligaments and the effect of distal clavicle resection.

To determine the role of the acromioclavicular ligaments in controlling scapular rotation about the distal clavicle and the effects of distal clavicle resection, we used 13 fresh shoulders consisting of the clavicle, acromioclavicular ligaments, coracoclavicular ligaments, and scapula. The range of motion was measured using a specially designed goniometer for each of the three orthogonal axes of rotation of the scapula with reference to the clavicle: anterior-posterior axial rotation, protraction-retraction, and abduction-adduction. We did two experiments involving sequential sectioning. Range of motion was measured in the intact shoulder and after each sectioning cut. The order of sectioning in Experiment 1 (six shoulders) was 1) the inferior acromioclavicular ligament, 2) removal of 5 mm of the distal clavicle, and 3) the superior acromioclavicular ligament. In Experiment 2 (seven shoulders) the order was 1) the superior acromioclavicular ligament, 2) removal of 5 mm of the distal clavicle, and 3) the inferior acromioclavicular ligament. The most important results were 1) only 5 mm of the distal clavicle needs to be resected to ensure that no bone-to-bone contact occurs in rotation postoperatively and 2) there was no difference in the end result (for range of motion in any of the three axes) whether the inferior acromioclavicular ligament or the superior acromioclavicular ligament was cut before removal of 5 mm of the distal clavicle.