Injuries to the clavicle (collarbone) and acromioclavicular (AC) joint are among the most common upper extremity sporting injuries. The clavicle attaches to the chest at the sternoclavicular (SC) joint, and to the scapula and arm at the AC joint.
The shoulder is a ball and socket joint, but the anatomy of the shoulder allows for an amazing amount of flexibility. The humeral head, or ball, sits on the glenoid, a very shallow socket. It resembles a golf ball on a tee. Because the socket is so shallow, the shoulder relies on the soft tissue around the shoulder for stability. The labrum, a thickened cartilage layer around the glenoid, and the ligaments and capsule, provide a majority of the stability to the shoulder. The muscles of the rotator cuff and scapula also provide stability.
An Acromioclavicular (AC) separation is a sprain of the ligaments that attach the clavicle to the scapula. The sprain can either be partial, with minimal separation of the clavicle and acromion, or complete, with complete separation of the clavicle and acromion. Treatment is based on the amount of displacement seen on radiographs.
The injury commonly occurs due to a direct blow to the lateral (outside) part of the shoulder, or by falling on an outstretched hand or elbow. AC joint injuries are particularly common in contact sports and biking.
Tenderness and swelling on the top of the shoulder at the AC joint is common after the injury. There is usually bruising after about 48 hours in the area as well. Early after the injury, it is often painful to move the arm and shoulder, as the entire area around the AC joint becomes inflamed.
Initial treatment of AC separations consists of medication and ice to relieve the pain and swelling associated with the initial injury. A sling is often used for 7-10 days to provide comfort while the AC joint begins to heal. Radiographs are usually obtained to determine the amount of displacement of the clavicle, and an MRI is occasionally ordered as well in order to make sure there is no injury to other parts of the shoulder.
Surgery is not usually necessary for AC separations, but is recommended in cases with complete disruption of the AC joint, or occasionally in patients with a partial tear of the ligaments and persistent pain despite appropriate treatment for 2-6 months following injury. Surgery consists of reconstructing the ligaments that hold the clavicle to the scapula. Return to sports is usually 4 to 6 months following surgery.
What to expect from a AC joint injury…
Return to sports is allowed when there is minimal pain and strength of the affected arm has returned to normal.
Even in partial sprains of the AC joint, a bump is common even after complete healing. The bump will get smaller over time, but rarely completely disappears.
Most people will recover completely from shoulder separations, with minimal pain and no loss of function.