Acromioclavicular Joint Anatomy and Biomechanics

Knowledge of the normal acromioclavicular (AC) joint anatomical relationships and biomechanics is important for the proper treatment of various AC joint pathologies. The AC joint is a complex diarthrodial articulation that is subject to a variety of atraumatic and traumatic conditions. The AC joint is supported by both capsular and extracapsular ligaments and dynamic muscular forces. The capsular ligaments provide stability in the anteroposterior direction as well as vertical stability with physiological loads. The extracapsular ligaments primarily provide vertical and compressive stability at supraphysiological loads and are commonly disrupted with high-grade AC joint injuries. Biomechanically, motion at the AC joint is a combination of translation, elevation, and rotational motions influenced by the complex interaction of scapulothoracic motion and guided by ligamentous restraints and dynamic muscular support. Disruption in normal AC joint anatomy or stability or both can affect normal biomechanics and lead to a variety of painful conditions.