Biomechanical Comparison of a Modified Weaver-Dunn and a Free-Tissue Graft Reconstruction of the Acromioclavicular Joint Complex

Abstract

Background: Most surgical reconstructions of the separated acromioclavicular joint do not address the injured ligaments and capsule of the acromioclavicular joint. Purpose: This study was undertaken to compare the biomechanical characteristics of a modified Weaver-Dunn reconstruction and an intramedullary acromioclavicular joint reconstruction that uses a free-tissue graft for reconstruction of both the coracoclavicular and acromioclavicular ligaments. Study Design: Controlled laboratory study. Methods: Each pair of 6 matched pairs of cadaveric shoulders was randomly selected for a modified Weaver-Dunn reconstruction on 1 side and the contralateral side was used for free-tissue graft reconstruction of the coracoclavicular and acromioclavicular ligamentous complexes. Anterior-posterior and superior-inferior acromioclavicular joint translation (in millimeters) was measured with acromioclavicular joint compressions of 10, 20, and 30 N, and with translational loads of 10 and 15 N both before and after acromioclavicular joint reconstruction. Load-to-failure testing was then performed for each construct. Repeated-measures analysis of variance (translational testing) and Wilcoxon signed rank test (load-to-failure testing), both with P = .05, were used for statistical analysis. Results: Mean anterior-posterior and superior-inferior translation of the intramedullary acromioclavicular joint reconstruction was significantly less than that of the modified Weaver-Dunn under all loading conditions ( P < .001 and P = .001, respectively), but was not significantly different from that of the intact state ( P = .656 and P = .173, respectively). Although the mean ultimate and yield loads and linear stiffness for the intramedullary acromioclavicular reconstruction were greater than that of the modified Weaver-Dunn reconstruction, this did not reach statistical significance ( P = .625, P = .625, and P = .625, respectively). Conclusion: Acromioclavicular joint reconstruction with free-tissue graft for both the coracoclavicular and acromioclavicular ligamentous complexes demonstrates initial stability significantly better than a modified Weaver-Dunn and similar to that of intact specimens. Clinical Relevance: This acromioclavicular joint reconstruction provides the surgeon with a relatively nondestructive option.