What Is It?

A shoulder dislocation occurs when the top of the bone of the upper arm (the humerus) moves out of its usual location in the shoulder joint. The shoulder joint is a type of joint called a ball-and-socket joint. The ball is the rounded top of the humerus, which fits into the socket — the cup-shaped outer part of the shoulder blade. A related injury, called a shoulder subluxation, occurs when the top of the humerus is only partially displaced, so that the arm bone is not totally out of its socket.

In some cases, a shoulder dislocation occurs because the arm has been pulled or twisted with extreme force in an outward, upward or backward direction. This extreme force literally pops the top of the humerus out of its socket. In other cases, a shoulder dislocation is the result of a fall on an outstretched arm, a direct forceful blow to the shoulder, a seizure or a severe electric shock. Shocks and seizures can cause shoulder dislocations because they produce extreme, unbalanced muscle contractions that can wrench the humerus out of place.

Doctors classify shoulder dislocations into three types, depending on the direction of the dislocation:

• Anterior dislocation — The top of the humerus is displaced forward toward the front of the body. This is the most common type of shoulder dislocation, accounting for more than 95 percent of cases. In young people, it is typically a sports-related injury, while in older people, it usually is caused by a fall on an outstretched arm.



• Posterior dislocation — The top of the humerus is displaced toward the back of the body. Posterior dislocations account for 2 percent to 4 percent of all shoulder dislocations, and are the type most likely to be related to electric shock and seizures. Posterior dislocations also can happen because of a fall on an outstretched arm or a blow to the front of the shoulder.



• Inferior dislocation — The top of the humerus is displaced downward. Inferior dislocations are the rarest of all shoulder dislocations, occurring in only one out of every 200 cases. They have been caused by various types of trauma in which the arm is pushed violently downward.

Overall, shoulder dislocations are the most common type of joint dislocation seen by emergency-room physicians, accounting for more than 50 percent of all dislocations treated in hospitals. They occur in 17 to 26 out of every 1,000 persons, particularly men 20 to 30 years old and women 61 to 80 years old.

Although 96 percent of all shoulder dislocations are related to trauma, the remaining 4 percent occur after ordinarily harmless motions, such as raising an arm or rolling over in bed. In these mysterious cases of dislocation without trauma, the real cause may be an abnormal looseness of the shoulder ligaments. Ligaments are fibrous bands of tissue that bind one bone to another. Ligament looseness is sometimes an inherited condition that can increase a person’s risk for dislocation in many body joints.

Symptoms of a dislocated shoulder include:

• Severe shoulder pain
• Limited motion of the shoulder — The shoulder joint cannot move normally because the head of the humerus is totally out of place.
• A distortion in the contour of the shoulder — In an anterior dislocation, the sideways silhouette of the shoulder has an abnormal squared-off appearance instead of its typical sloping, rounded contour. In a posterior dislocation, the front of the shoulder may look abnormally flat.
• A hard knob under the skin near the shoulder — This knob is the top of the humerus that has popped out of its socket.
• Shoulder bruising or abrasions if an impact has caused your injury

The doctor will examine both shoulders, comparing your injured shoulder with your uninjured one. The doctor will check for swelling, shape changes, abrasions, bruising, pain with movement, tenderness and limitation of motion at the shoulder joint. The doctor also will gently press and feel the area around your shoulder to locate the displaced head of the humerus under the skin. In addition, since many important blood vessels and nerves travel through your shoulder area, your doctor will check the strength of the pulses at your wrist and elbow and check the muscle strength and skin feeling in your arm, hand and fingers. In particular, your doctor will look for numbness on the outside of your upper arm, a sign of injury to the axillary nerve, which is vulnerable to injury in a shoulder dislocation.

If the results of your physical examination suggest that that you have a dislocated shoulder, your doctor will order shoulder X-rays to confirm the diagnosis.

Once your displaced humerus is slipped back into its socket, your ability to move your shoulder probably will improve immediately and the full range of motion should return fully within six to eight weeks, provided that you faithfully follow an exercise program. Although most shoulder strength usually returns within three months, regaining full strength may take up to one year.

If you have had a dislocated shoulder, you may be able to prevent a repeat injury by doing shoulder-strengthening exercises that are recommended by your doctor or physical therapist. If you have had one shoulder dislocation you are at risk of another, particularly if you play a contact sport. By one count, 65 percent to 90 percent of young athletes who had one shoulder dislocation had another dislocation later. In people who do not play contact sports, repeat dislocations occur in about 30 percent of shoulder dislocations.

When the arm bone is forced out of its socket, it remains attached to the muscles of the shoulder blade and upper chest. These muscles pull the arm bone against the shoulder and chest, even when the bone is out of its socket and off-center. If these muscles are in spasm, they need to be relaxed before the doctor can move the arm bone back into its socket. Your doctor may give you medications to ease your pain and relax your shoulder muscles. Then the doctor will pull carefully against these muscles until the head of your humerus slips back into its socket. Sometimes, doctors use arm weights on the side of the dislocation to make it easier to extend these tight muscles. This treatment, with or without the weights, is called closed reduction.

Once your shoulder joint is back in its normal position, you will rest your arm in a sling for one to four weeks. Teen-agers wear the sling longer than older patients. You also will begin a physical-therapy program to restore the normal strength and range of motion in your shoulder joint.

If you continue to have severe shoulder pain after closed reduction, or your injured shoulder is loose and unstable in spite of physical therapy, you may need surgery to repair the fibrous tissues that support your shoulder joint. In some cases, this surgery can be done through a small incision, using an arthroscope.

Call your doctor immediately if you cannot move your shoulder following a fall or other traumatic injury, or if your shoulder is painful, swollen, tender or unusually shaped.

The prognosis depends on many factors, including the severity of your shoulder injury, your age and your participation in athletic activity. For example, if you are a teen-age athlete and you play contact sports such as football or hockey after a shoulder dislocation, your overall risk of a second shoulder dislocation may be as high as 90 percent. With repeated injury, you may also be at high risk of developing shoulder instability that requires surgical repair. Surgery usually restores the shoulder’s stability and reduces the risk of future dislocation to 5 percent or less.

If you are an older patient and you have an uncomplicated shoulder dislocation, your risk of a second dislocation is low, with repeat dislocations occurring only about 25 percent of the time for people in their 30s and less often for older age groups.

Diseases and Conditions Center

All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.