The Acromioclavicular joint (ACJ) is part of the shoulder complex. It is situated on top of the shoulder joining the clavicle (collar bone) to the scapular (shoulder blade). The joint can be separated (dislocated) as a result of injury- these said injuries being among the most common upper extremity sporting injuries. Ligaments are torn and in severe cases surgery is required to stabilize the joint.
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.
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.