The clavicle, being a strut from the anterior chest wall to the shoulder, articulates with the superior and lateral projection from the scapula called the acromion. This articulation is called the acromioclavicular joint. Problems in the AC joint can lead to abnormal scapular biomechanics and can lead to shoulder dysfunction and pain.
AC joint arthritis: The acromioclavicular joint can become arthritic due to abnormal stress and wear on the articular cartilage on either side of the joint ( end of the clavicle or the articular facet of the acromion ). Degeneration of the joint does occur with the aging process, with nearly 90% of people showing some signs of degeneration by the age of 35. People who repetitively lift and work overhead seem to be predisposed to developing accelerated degenerative arthritis in the AC joint.
Distal clavicle osteolysis: This condition, which is better known as “weightlifter’s shoulder”, is a painful deterioration of the distal end of the clavicle as a result of stress injury to the end of the clavicle. The abnormal stress leads to microfractures of the end of the bone, and, eventually, bone from the distal clavicle resorbs and cysts in the bone develop. While the condition is commonly seen in weightlifters with shoulder pain, the condition can also occur in overhead workers, laborers, military personnel, and overhead athletes.
Treatment options: Conservative options for AC joint arthritis and distal clavicle osteolysis consist of anti-inflammatory medications, activity modifications, periodic corticosteroid injections, and physical therapy, particularly if scapular mechanics are affected. For patients with chronic symptoms that continue to adverse affect quality of life and function, surgery can be considered. The surgery consists of an arthroscopy with debridement and distal clavicle resection.
Watch a video of an arthroscopic distal clavicle resection
Left shoulder complete AC joint separation 
AC joint Separation: Falls directly onto the shoulder or trauma from a motor vehicle accident can rupture the suspensory ligaments of the shoulder as well as the ligaments that stabilize the distal clavicle. When the ligaments completely rupture, the end of the clavicle will appear to be “high riding”, but in fact, the clavicle is in a normal position and the entire shoulder girdle (scapula and humerus). These injuries are quite common in athletes, especially hockey players. It has been estimated that the majority of NHL hockey players has sustained an AC joint separation during their career. Partial separations are usually successfully treated conservatively. Residual symptoms are common for 6-12 months. Injections can be done to help with residual symptoms. Complete AC joint separations are also treated conservatively, although with significant displacement and stripping of muscles from the clavicle, surgical stabilization is offered. Reconstruction of the coracoclavicular ligaments using a tendon graft is an effective way to restore function in symptomatic patients. Following surgery, patients are treated in a sling immobilizer for 5 weeks. Physical therapy is initiated to restore motion, followed by strength.
Watch a video of reconstruction of the coracoclavicular ligaments/AC joint