From Jonathan Cluett, M.D.,
Your Guide to Orthopedics.
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About.com Health's Disease and Condition content is reviewed by Kate Grossman, MD

A shoulder separation is an injury to the acromioclavicular joint on the top of the shoulder. The shoulder joint is formed at the junction of three bones: the collarbone (clavicle), the shoulder blade (scapula), and the arm bone (humerus). The scapula and clavicle form the socket of the joint, and the humerus has a round head that fits within this socket.

A shoulder separation occurs where the clavicle and the scapula come together. The end of the scapula is called the acromion, and the joint between this part of the scapula and clavicle is called the acromioclavicular joint. When this joint is disrupted, it is called a shoulder separation. Another name for this injury is an acromioclavicular joint separation, or AC separation.

Is a shoulder separation the same as a shoulder dislocation?
No! These two injuries are commonly confused, but they are very different conditions. As described above, the shoulder joint is located at the junction of three different bones: the clavicle, the scapula, and the humerus. In a shoulder separation, the junction of the clavicle and scapula is disrupted. In a shoulder dislocation, the humerus (arm bone) is displaced from the socket. Not only are the injuries different in anatomic terms, but the implications for treatment, recovery, and complications are also different.

How does a shoulder separation occur?
A shoulder separation is almost always the result of a sudden, traumatic event that can be attributed to a specific incident or action. The two most common descriptions of a shoulder separation are either a direct blow to the shoulder (often seen in football, rugby, or hockey), or a fall on to an outstretched hand (commonly seen after falling off a bicycle or horse).

What are the symptoms of a shoulder separation?
Pain is the most common symptom of a separated shoulder, and is usually severe at the time of injury. Evidence of traumatic injury to the shoulder, such as swelling and bruising, are also commonly found.

The diagnosis of shoulder separation is often quite apparent from hearing a story that is typical of this injury, and a simple physical examination. An x-ray should be performed to ensure there is no fracture of these bones. If the diagnosis is unclear, an x-ray while holding a weight in your hand may be helpful. When this type of x-ray is performed, the force of the weight will accentuate any shoulder joint instability and better show the effects of the separated shoulder.

Are all separated shoulders the same?
No. Separated shoulders are graded according to the severity of the injury and the position of the displaced bones. Shoulder separations are graded from type I to VI:

• Type I Shoulder Separation:
  A type I shoulder separation is an injury to the capsule that surrounds the AC joint. The bones are not out of position and the primary symptom is pain.

• Type II Shoulder Separation:
  A type II shoulder separation involves an injury to the AC joint capsule as well as one of the important ligaments that stabilizes the clavicle. This ligament, the coracoclavicular ligament, is partially torn. Patients with a type II separated shoulder may have a small bump over the injury.

• Type III Shoulder Separation:
  A type III shoulder separation involves the same type of injury as a type II separated shoulder, but the injury is more significant. These patients usually have a large bump over the injured AC joint.

• Type IV Shoulder Separation:
  A type IV shoulder separation is an unusual injury where the clavicle is pushed behind the AC joint.

• Type V Shoulder Separation:
  A type V shoulder separation is an exaggerated type III injury. In this type of separated shoulder, the muscle above the AC joint is punctured by the end of the clavicle causing a significant bump over the injury.

• Type VI Shoulder Separation:
  A type VI shoulder separation is also exceedingly rare. In this type of injury the clavicle is pushed downwards, and becomes lodged below the corocoid (part of the scapula)

Read on for more about the treatment of different types of shoulder separations...