What is the A.C. Joint?

If you have not yet reviewed the general shoulder anatomy page, please do so now. The A.C. Joint (Acromioclavicular Joint) is one of the two joints in the shoulder. The A.C. joint is the joint between the scapula (the shoulder blade) and the clavicle (the collar bone). The A.C. joint can be injured in varying degrees. A Grade 1 injury is defined as a simple sprain of the ligaments. A Grade 2 injury occurs when one of the ligaments of the joint is actually torn and a Grade 3 injury results in an obvious bump on the shoulder as a result of an A.C. joint dislocation (or separation). This occurs when the ligaments around the joint as well as the ligaments that connect the clavicle to the scapula are torn.

How is the A.C. Joint injured?

A.C. joint injuries are common among the snowboarding community, as well as in other sports activities where falls on the shoulder are common. When a person falls on their shoulder, the scapula is pushed further into the back. However, these injuries are caused because of the way the clavicle is attached. The clavicle is attached to the rib cage, and cannot move a significant amount as the scapula can. When the scapula is pressed into the back, the ligaments and muscles between the scapula and the clavicle are strained, and sometimes torn as a result.

What are the symptoms of an A.C. Joint injury?

Because of the varying degrees of injury in this joint, the symptoms vary. If you have any of these symptoms, you seek the care of an orthopedist to ensure that the problem is diagnosed properly.

Symptoms for a Grade 1 injury will usually include tenderness around the joint and a very minimal amount of swelling. If the injury is a grade 2 or grade 3 injury, you will probably notice considerable swelling and may observe a bluish discoloration of the skin a few days after the injury due to bruising. In a grade 3 injury you may experience a popping sensation due to loose joint shifting. As stated above, if the joint is completely dislocated, there will usually be a noticeable bump on the shoulder.

How is an A.C. joint injury diagnosed?

An A.C. joint injury is best diagnosed with the physical examination by an orthopedist. X-rays will show your orthopedist if the A.C. joint is dislocated as well as show whether any bones were fractured in the accident. An MRI may be taken to see which, if any ligaments are torn and to what extent they are torn.

How is an A.C. Joint injury treated?

Treatment for a grade 1 or grade 2 injury usually consists of an arm sling and anti-inflammatory medication (such as ibuprofen) until the sprain or tear heals. The shoulder should be relatively pain free within 3 weeks.

The treatment of a grade 3 separation will be discussed with you by your orthopedist. You may opt to have the joint surgically repaired, in which case the orthopedic surgeon will relocate the joint and repair the torn ligaments. Surgical repair will be most beneficial to athletes who use their shoulders regularly. However, you may choose to let the injury heal on its own. Your orthopedist will discuss these options with you as well as the pros and cons of surgical and the non-surgical aspects of healing to help you make the best decision for yourself.