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

Excessive posterior translation of the residual clavicle after distal clavi cle resection can be associated with significant postoperative pain. Althou gh the acromioclavicular capsule has been identified as the primary restrai nt to translation of the clavicle along this axis, the individual contribut ions of the anterior, posterior, superior and inferior components of the ca psular ligament have not been established. The purpose of this study was to define the relative roles of the individual acromioclavicular capsular lig aments 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 app aratus which, when attached to a standard servohydraulic materials testing device, allowed translation of the distal clavicle along the anteroposterio r axis of the arcromioclavicular joint (ie, parallel to the articular surfa ce). Resistance to posterior displacement was measured For standardized dis placements in the normal specimens and after serial sectioning of each of t he acromioclavicular ligaments was performed. Sectioning of the anterior an d inferior capsular ligaments had no significant effect on posterior transl ation 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%, resp ectively, of the Force required to achieve a given posterior displacement. To avoid excessive posterior translation of the clavicle after distal clavi cle excision, surgical techniques that spare the posterior and superior acr omioclavicular capsular ligaments should be used.