Biomechanical and Radiographic Analysis of Partial Coracoclavicular Ligament Injuries

Background A spectrum of acromioclavicular joint injuries may exist between type II acromioclavicular joint disruption (coracoclavicular strain) and type III acromioclavicular joint injuries (coracoclavicular disruption). This may help explain the variability in outcomes seen in patients with type II acromioclavicular injuries. Hypothesis Injury to either the conoid or trapezoid ligaments would lead to instability of the acromioclavicular joint after complete acromioclavicular joint injury. A secondary hypothesis was that the resulting instability could be recognized with Zanca radiographs. Study Design Controlled laboratory study. Methods The acromioclavicular ligaments were sectioned in 40 cadaveric shoulder specimens. Ten intact specimens were loaded to failure to evaluate the normal failure patterns of the coracoclavicular ligaments. Thirty specimens then had either the conoid or trapezoid ligament sectioned after creation of complete acromioclavicular joint injury. Preinjury and postinjury radiographs and stability testing quantified the effect of coracoclavicular joint injury on acromioclavicular joint stability. Results During failure testing, the conoid always failed first. Sectioning of the conoid led to significant increases in posterior and superior displacement on radiographs and with materials testing. Sectioning of the trapezoid led to significant increases in posterior displacement for materials testing and superior displacement on radiographs. Conclusion Sectioning of the acromioclavicular ligaments in conjunction with partial disruption of the coracoclavicular ligament complex led to significant changes in both radiographic and mechanical measures of acromioclavicular stability. The conoid fails first when a load is applied to the coracoclavicular complex in a superior direction. Clinical Relevance Zanca radiograph may detect incomplete injury to the coracoclavicular ligaments associated with acromioclavicular disruption.