The acromioclavicular capsule as a restraint to posterior translation of the clavicle: a biomechanical analysis.

Excessive posterior translation of the residual clavicle after distal clavicle resection can be associated with significant postoperative pain. Although the acromioclavicular capsule has been identified as the primary restraint to translation of the clavicle along this axis, the individual contributions of the anterior, posterior, superior, and inferior components of the capsular ligament have not been established. The purpose of this study was to define the relative roles of the individual acromioclavicular capsular ligaments in preventing posterior translation of the distal clavicle in normal acromioclavicular joints in a human cadaver model. Six fresh-frozen human cadaveric acromioclavicular joints were mounted on a specially designed apparatus which, when attached to a standard servohydraulic materials testing device, allowed translation of the distal clavicle along the anteroposterior axis of the acromioclavicular joint (i.e., parallel to the articular surface). Resistance to posterior displacement was measured for standardized displacements in the normal specimens and after serial sectioning of each of the acromioclavicular ligaments was performed. Sectioning of the anterior and inferior capsular ligaments had no significant effect on posterior translation at the 5% significance level. However, sectioning of the superior and posterior ligaments had statistically significant effects (P < .05). These capsular structures contributed 56% +/- 23% (+/- SEM) and 25% +/- 16%, respectively, of the force required to achieve a given posterior displacement. To avoid excessive posterior translation of the clavicle after distal clavicle excision, surgical techniques that spare the posterior and superior acromioclavicular capsular ligaments should be used.