- Planar diarthrodial joint
- Formed by the junction of the anteromedial acromion and lateral clavicle
- Clavicle has 3 ossification centers
- Beginning at 5 to 6 weeks’ gestation
- Clavicular ossification often is not complete until 25 years of life
- Acromion has 4 ossification centers
- Preacromion, meta-acromion, and mesoacromion fusing together by 18 years of life
- A fibrocartilaginous disk cushions the joint
- The disk is composed of 75% water, 20% collagen (90% of which is type I, with minor contributions from types II, III, and IV), and 5% proteoglycans, elastin, and other cells
- Degeneration of the intra-articular meniscus is thought to contribute to osteoarthritis
- Commonly observed in patients over the age of 50 years, begins as early as the second decade of life
- Acromioclavicular Ligament
- Resist 50% of anterior and 90% of posterior displacement
- Coracoclavicular Ligaments
- Primary: resist superior and axial translation
- Secondary: resist anterior and posterior translation in the absence of AC ligaments
- Blood Supply
- Suprascapular Artery
- Thoracoacromial Artery
- Branches of the Suprascapular Nerve
- Ogata, S, Uhthoff, HK. The early development and ossification of the human clavicle—an embryologic study. Acta Orthop Scand. 1990;61(4):330-334.
- Warner, JJP, Beim, GM, Higgins, L. The treatment of symptomatic os acromiale. J Bone Joint Surg Am. 1998;80(9):1320-1326.
- Brys, P, Geusens, E Scapular, clavicular, acromioclavicular and sternoclavicular joint injuries. In: Vanhoenacker, FN, Maas, M, Gielen, JL, eds. Imaging of Orthopedic Sports Injuries. Berlin, Germany: Springer-Verlag; 2007:169-182.
- DePalma, AF . The role of the discs of the sternoclavicular and acromioclavicular joints. Clin Orthop Relat Res. 1959;13:7-12.