Biomechanical Evaluation of the Acromioclavicular Capsular Ligaments and Reconstruction with an Intramedullary Free Tissue Graft

Abstract

Background Multiple techniques have been reported to treat chronic acromioclavicular joint injuries. However, many have failed to restore native stability, and few have addressed reconstructing the acromioclavicular ligaments. Hypothesis An intramedullary free semitendinosus graft reconstruction of the acromioclavicular ligaments will demonstrate joint stability comparable with that of the intact acromioclavicular joint. Study Design Controlled laboratory study. Methods Six matched pairs of cadaveric specimens with only the acromioclavicular capsule/ligament intact were tested at 10 N and 15 N in the anteroposterior and superoinferior directions under acromioclavicular joint compression loads of 10 N, 20 N, and 30 N. One of each pair randomly underwent reconstruction of the acromioclavicular ligaments with an intramedullary free semitendinosus graft, and the translational testing was repeated. Both the intact and reconstructed specimens then underwent load-to-failure testing via superior clavicle distraction at a rate of 50 mm/min. Results The reconstructed specimens reproduced the stability of the intact specimens during all translational and joint compression load trials. Progressively decreased translation was observed for the reconstructed specimens that reached statistical significance (P < .05) in the anteroposterior direction at 10 N of joint compression under 10-N and 15-N translation loads and in the superoinferior direction at 10 N of joint compression and 10-N translational load. With regard to load-to-failure testing, the reconstructed specimens demonstrated significantly lower (P < .05) values for linear stiffness, yield load, ultimate load, and energy absorbed, ranging from 40% to 48% of the values for the intact specimens. Conclusion Intramedullary free semitendinosus graft reconstruction of the acromioclavicular ligaments reproduced anteroposterior and superoinferior translational stability and partially reproduced load-to-failure characteristics. Clinical Relevance When surgical intervention after higher grade acromioclavicular joint injuries is required, reconstruction of the acromioclavicular ligaments with an intramedullary free semitendinosus graft, in addition to reconstructing the coracoclavicular ligaments, may result in improved stability of the joint complex, improved maintenance of joint reduction, and increased patient satisfaction.