Acromioclavicular joint

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.

Ligaments

The joint is stabilized by three ligaments:

Injuries

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, ultimate frisbee, and biking. When incurred during a game of ultimate frisbee, the injury commonly occurs in conjunction with the activity known as a lay out. The dislocation is classified on a scale of 1 to 6, with 6 being the most severe. The most common mechanism of injury is a FOOSH (Fall on a outstretched hand).

Type 1

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.

Type 2

A type 2 AC dislocation involves tearing of the ligaments, which causes a noticeable bump on the shoulder. This bump is called a "Piano Key" sign. By pressing on the sternal aspect of the clavical you force the acromial end to pop up (due to the tearing of the AC ligament) illiciting a piano key sign. 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.

Types 3-6

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.

External links

Overview and diagram