The principal causes of AC joint arthritis are overuse injuries or previous trauma to the AC joint. Any activity that can put pressure on the joint, either normal or excessive, may eventually cause this condition.
Constant overhead lifting, such as is engaged in by weightlifters or manual laborers who work overhead can increase the incidence of the disease. Other susceptible individuals are athletes participating in contact sports or engaging in any activity which may result in a fall on the end of the shoulder.
Typical symptoms of AC joint arthritis are pain and tenderness on the top of the shoulder around the AC joint. Sleeping on the side may cause pain and restlessness. There may be a decrease in shoulder motion. Compression of the joint, such as bringing the arm across the chest may result in increased pain.
First-line treatment consists of non-steroidal anti-inflammatory drugs (NSAIDs) and activity modification with physiotherapy. Steroid and local anesthetic injections are quite useful in recalcitrant cases.