The acromioclavicular joint, or AC joint, is a joint at the top of the shoulder. It is the junction between the acromion (part of the scapula that forms the highest point of the shoulder) and the clavicle. This article is about a joint in zootomical anatomy. ... In human anatomy, the shoulder joint is composed of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone) (see diagram). ... The acromion process, or simply the acromion, is an anatomical feature on the scapula. ... Left scapula - front view () Left scapula - rear view () In anatomy, the scapula, or shoulder blade, is the bone that connects the humerus (arm bone) with the clavicle (collar bone). ... Left clavicle - from above Left clavicle - from below In human anatomy, the clavicle or collar bone is a bone that makes up part of the shoulder girdle. ...

The joint is stabilized by three ligaments: The acromioclavicular ligament, the coracoclavicular ligament, and the capsule ligament. A ligament is a short band of tough fibrous connective tissue composed mainly of long, stringy collagen fibres. ...

A common injury to the AC joint is dislocation, or AC shoulder separation. This occurs often in sports like football, soccer, horseback riding, mountain biking, and biking. The dislocation is classified on a scale of 1 to 6, with 6 being the most severe. A type one AC dislocation involves trauma to the ligaments that form the joint, but no severe tearing or fracture. It is commonly referred to as a sprain. Most doctors treat this type of dislocation with anti-inflammatory drugs and the placement of the arm in a sling.

A type 2 AC dislocation involves tearing of the ligaments, which causes a noticeable bump on the shoulder. Severe pain and loss of movement are common. Treatment is typically an arm sliing, bed rest, and anti-inflammatory drugs. Most people recover full motion of the shoulder and arm within 6 to 8 weeks, often with the assistance of physical therapy.

More severe and less treatable are type 3 through 6 separations. These involve the complete tearing of the ligaments at the AC joint and those under the scapula that hold the shoulder in place, and the clavicle bone left floating. A significant bump appears and movement may be very restricted. Pain can be very severe in these instances. Many doctors will not do surgery on a type 3 separation as it is debatable how effective the surgery is. The most common surgery is the Weaver-Dunn, which involves the grafting of tendons and muscles from the leg. Variations include the use of synthetic sutures to assist in the strengthening of the grafts. Type 4 through 6 separations always result in surgery. The Weaver-Dunn procedure is 50% successful, with the best results in males (females tend to have more clavicle breakage after the surgery). Physical therapy is always recommended after surgery, and most patients get flexibility back, although somewhat limited.