Shoulder separations and dislocations

Have you ever wondered what the difference was between a shoulder separation and a dislocation? Also, why are separations and dislocations virtually unique to the shoulder area? What is it about the anatomy of this area that lends itself to reinjury? Finally, can shoulder separations and dislocations be prevented? Join Dr. Bruce Moseley, team physician of the Houston Rockets and a member of the Association of Professional Team Physicians (PTP) as he addresses these and other questions about one of the most complex joints in the body -- the shoulder.

How does the shoulder dislocate or separate?

Dr. Moseley: Shoulder dislocations and separations are two separate injuries and should not be confused with one another. The terms "dislocation" and "separation" should not be used interchangeably although this mistake is frequently seen in newspapers and magazines.

The shoulder has two joints, the ball-and-saucer glenohumeral joint, and the joint on top of the shoulder called the acromioclavicular joint. Dislocations occur at the glenohumeral joint, while separations occur at the acromioclavicular joint.

A dislocation occurs when the "ball" of the humerus slips out of the "saucer" of the glenoid. The humerus is the upper-arm bone, and the head of the humerus (the "ball") is round and rotates in the center of the glenoid during normal shoulder motion. Normally, the ball of the humerus stays in the center of the saucer-like glenoid, but instability results when the ball dislocates or comes out of the saucer.

A separation occurs when the end of the clavicle separates from the adjacent acromion. The clavicle is the "collar bone," and the outer end of the clavicle is connected to the upper part of the shoulder blade at the acromion. Hence, the joint is known as the acromio-clavicular or A-C joint. A separation occurs when the end of the clavicle separates and elevates away from the acromion.

Why are these injuries more common in the shoulder than in other joints?

Separations are unique to the A-C joint and as such can only occur in the shoulder.

What causes dislocations and separations?

Dr. Moseley: Injuries or trauma are the cause of both separations and dislocations. A dislocation usually occurs when the arm is out away from the body and is forced backward behind the body. Imagine a football linebacker with his arms out away from his body poised to tackle the opposing player. Then imagine the opposing player is Ricky Williams who just runs right through the arm tackle and forces the linebacker's arm backward and dislocates the shoulder.

A separation usually occurs when a person falls down hard right on top of his shoulder. Imagine a bicycle rider who has the front wheel of his bike stop suddenly in a rut and the rider goes head first over the handlebars and falls on top of his shoulder. The crash of the rider's body weight forces the clavicle to separate from the acromion.

What are the symptoms?

Dr. Moseley: A dislocation causes severe pain, deformity in the glenohumeral joint, and an inability to rotate the arm because the humerus is locked out of place.

A separation causes severe pain and a deformity on top of the shoulder where the clavicle sticks up. Since the humerus is not involved, the arm can still rotate.

How are they treated?

Dr. Moseley: Dislocations require a reduction where the humerus (arm) is pulled back into the center of the glenoid. If the shoulder dislocates more than once, it is considered a "recurrent" dislocation, and these are usually fixed surgically to prevent the shoulder from coming out of place again.

Separations are usually left alone unless the deformity is severe. In cases of severe deformity, the clavicle can be surgically reduced and fixed.

What is the prognosis and how common are recurrences?

Dr. Moseley: Dislocations have frequent recurrences, especially in teenagers and young adults. If surgery is done to fix the recurrent dislocations, the prognosis is excellent, with approximately 95 percent of patients having full return of function and no further recurrences.

The prognosis for separations is excellent for return of function, although the bump or deformity on top of the shoulder remains. Since this bump doesn't usually affect function, it is safe to ignore it.

Dr. Bruce Moseley, a member of the Association of Professional Team Physicians (PTP), is a team physician for the Houston Rockets. Dr. Moseley received his undergraduate degree from the University of Texas at Austin and his M.D. from the University of Texas Health Science Center's Southwestern Medical School in Dallas. He completed a residency in orthopedic surgery at the University of Utah in Salt Lake City and was also was awarded a fellowship in sports medicine at the Kerlan-Jobe Orthopedic Clinic in Inglewood, Calif.

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