The acromio-clavicular joint can develop arthritis (ACJ arthritis) secondary to wear and tear. Although most of the people with this condition do not have symptoms, few people develop pain and difficulty with shoulder movements. It is usually treated with combination of physical therapy and steroid injection. In resistant cases, your surgeon may suggest arthroscopic excision of acromio-clavicular joint where small portion (5-8 mm) of the bone is removed from end of the collar bone (clavicle).