Shoulder Dislocation
Key points
- 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 doctor will examine both shoulders, comparing your injured shoulder with your uninjured one.
- 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.
- 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.
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.
Frequently asked questions
What is shoulder dislocation?
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.
What are the symptoms of shoulder dislocation?
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
How is shoulder dislocation diagnosed?
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.
Written and revised by
David Cohen, M.D.
Our doctors write and review articles for accuracy and keep them up to date.
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