Epidemiology, anatomy, biomechanics and imaging of acromioclavicular joint injuries

Current techniques of acromioclavicular (AC) joint repair primarily focus on the reconstruction of the coracoclavicular (CC) ligaments. However, it is not clear if this approach is sufficient to restore vertical as well as horizontal AC joint stability and kinematics. This review focuses on the epidemiology of AC joint injuries and the coincidence of intra-articular pathologies. Furthermore, the clinically relevant anatomy and the pathomechanism of AC joint instability are described. The biomechanical characteristics of current procedures as they have been revealed by in vitro investigations are summarized. As a basic result, neither selective repair of the CC ligaments nor selective repair of the AC ligaments could be shown to restore both vertical and horizontal joint stability. Similar to the intact ligaments CC repair primarily provides vertical joint stability while AC repair is able to restore horizontal stability. In conclusion a biomechanically effective treatment of AC joint separation should analyze the individual instability pattern in the first step. Therefore, the radiological standard according to Rockwood should be supplemented by specific stress x-rays for quantification of dynamic horizontal AC joint instability. In the second step an adequate surgical treatment considering CC and AC stabilization should be performed meeting the individual patient requirements.