Acromioclavicular joint (AC) injuries are associated with damage to the joint and surrounding structures.
The acromioclavicular joint, together with the sternoclavicular joint, connects the upper limb to the skeleton.
The support of the acromioclavicular joint is provided by the ligament and muscle surrounding the joint. The capsule surrounding the acromioclavicular joint is strengthened by the acromioclavicular ligaments. The joints are acromioclavicular ligaments that provide horizontal stability.
The coracoclavicular ligaments consist of two parts, the lateral trapezoid, and the medial conoid, and connect the distal lower clavicle to the coracoid process of the scapula. The coracoclavicular ligament is the main stabilizing ligament of the upper limb.
Acromioclavicular joint injuries occur at all ages, but are most common in the 20-40 year age group, 5x times more common in men than women. It is a common contact sports injury in young male athletes (1).
There are two main mechanisms of acromioclavicular joint injury; direct and indirect (2). A direct blow or fall to the shoulder results in a superior force on the acromion with restricted clavicular movement in the joint, the acromion is forcibly pushed down and medially relative to the clavicle. It can occur indirectly as a result of a fall on the hand or elbow, causing the humerus to be pushed into the acromion, resulting in lower-grade injuries that typically protect the coracoclavicular ligament.
Imaging can be used to classify acromioclavicular injuries and is the most widely used Rockwood classification.
References and Further Reading
- Dyan V. Flores, Paola Kuenzer Goes, Catalina Mejía Gómez et-al. Imaging of the Acromioclavicular Joint: Anatomy, Function, Pathologic Features, and Treatment. (2020) RadioGraphics. 40 (5): 1355-1382.
- Vanhoenacker F, Maas M, Gielen JL. Imaging of Orthopedic Sports Injuries. (2006)
- Tintinalli’s Emergency Medicine, A Comprehensive Study Guide 9th edition. ( 2019)