The anatomy of the shoulder allows the greatest range of motion of all the joints, and this anatomy places it at risk for dislocation. The shoulder is similar to a golf ball on a golf tee. The humeral head (golf ball) which sits in a shallow, relatively small, cup-shaped socket called the glenoid (tee). The labrum is a bumper-like rim of cartilage around the bone that deepens the cup and helps keep the humeral head in the socket.
Three main ligaments and the rotator cuff muscles and tendons wrap around the humeral head to improve the stability of the shoulder joint. When the shoulder dislocates, any of these structures may be injured. Repetitive partial dislocation (subluxation) can also injure these structures and cause pain and the feeling of instability. Persistent instability and pain occurs when the labrum is torn, the ligaments are torn or stretched, or when there are problems with the rotator cuff or the bones of the shoulder.
What happens when the shoulder dislocates?
Whenever a shoulder dislocates, the ligaments and labrum tear. Most commonly, shoulder dislocations occur when the arm is wrenched backward forcefully levering the shoulder out of the joint. The shoulder most often dislocates anteriorly (forward), but may also dislocate posteriorly. This can happen from a fall on an outstretched arm or from a direct blow to the front of the shoulder.
How is the shoulder joint “relocated”?
Sometimes, you can use your own muscles to “pull” the humeral head back into the socket. However, after the shoulder joint has been dislocated, the muscles of the shoulder will spasm and not allow any movement of the dislocated humerus.
The dislocated humerus needs to be returned (relocated) to the socket as soon as safely possible. In most instances, you will need to be taken to an emergency facility. A physician will give medication to relax the shoulder muscles and then manually relocate the shoulder.
Treatment after dislocation consists of the use of a sling or shoulder immobilizer to rest the injured limb.
Will my shoulder dislocate again?
Unfortunately, once you have dislocated your shoulder, the chances of it happening again are greater, especially if you are active in sports. Ligaments and tendons may stretch during a dislocation, making the shoulder unstable. Whether or not your shoulder will re-dislocate depends on several factors including age, athletic activity, fractures and bony lesions, and type of sport played. Previous studies have shown that the risk of re-dislocation is approximately:
~ 90-95% if less than 20 years old
~ 60-85% if less than 30 years old
~ 95% if bone loss is present
When is surgery necessary?
Surgery is indicated when the shoulder instability becomes a disability for the patient. The need for surgery depends upon the functional demands of the patient and the degree of instability present. Typically, surgery is not done unless a conservative program of exercise has failed. Patients who have repeated shoulder dislocations are the usual candidates for surgical repair.
What does the surgery involve?
Surgery attempts to restore an anatomical balance to the joint and address the problems that are causing the instability. The surgery focuses on repairing the structures that were torn at the time of the injury. In some situations, arthroscopic techniques may be used, but in other situations, open repair is the favored technique.
Results and Risks of Surgery
The goal of surgery is to restore stability while maintaining mobility and restoring pain-free functional use of the shoulder in daily activities as well as sports and recreational activities. Typical success rates of surery for shoulder instability vary from 90 to 95 %. In addition to the general surgical risks, the most common problems following surgery for a shoulder dislocation are shoulder stiffness or another dislocation.
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