Shoulder Instability, Posterior

Description

Posterior shoulder instability is an injury to the shoulder joint that causes the upper arm (humerus) to be displaced from its normal position in the center of the socket (glenoid), so that the joint surfaces no longer touch each other. This uncommon dislocation occurs at the back of the shoulder, where the humerus sits behind the glenoid.

The shoulder is like a golf ball on a tee, and because the shoulder has more motion than any other large joint in the body, it is the most commonly dislocated large joint. A few of the many structures that provide shoulder stability include the cartilage rim (labrum), which helps provide depth to the socket; the capsule, with thickenings that are the ligaments of the shoulder; and the muscles of the rotator cuff, which surround the shoulder. To dislocate the shoulder, the rotator cuff muscles must be stretched or torn, the capsule and ligaments must be stretched, and often the labrum is pulled off the glenoid. Posterior subluxation of the shoulder is more common than dislocation, but both are much less common than anterior dislocation. Subluxation is when the ball of the humerus does not stay centered in the socket with shoulder motion and feels as if it is slipping out of place.

Common signs and symptoms

• Severe pain in the shoulder at the time of injury

• Loss of shoulder function and severe pain when attempting to move the shoulder

• Feeling as if the shoulder is slipping out of place

• Tenderness and swelling in the back of the shoulder

• Deformity of the shoulder, specifically a fullness in the back of the shoulder

• Inability to turn the arm outward

• Numbness or paralysis in the upper arm and deltoid muscle from pinching, stretching, or pressure on the blood vessels or nerves

• Decreased or absent pulse at the wrist because of blood vessel damage (rare)

Causes

• A direct blow to the shoulder

• A backward force on an outstretched arm, such as with blocking in football

• End result of a severe shoulder sprain

• Congenital abnormality (birth defect), such as a shallow or malformed joint surface

• Powerful muscle twisting or violent muscle contraction, such as with an epileptic seizure or electrocution

• Some people can willfully produce a recurrent dislocation.

Factors that increase risk

• Contact sports (football, wrestling, basketball)

• Sports that require forceful lifting, hitting, or twisting (swimming, volleyball, softball)

• Previous shoulder dislocations or sprains

• Shoulder fracture

• Repeated shoulder injury of any kind

• Poor physical conditioning (strength, flexibility)

Preventive measures

• Appropriately warm up and stretch before practice and competition.

• Maintain appropriate conditioning that includes shoulder strength, flexibility and endurance, and cardiovascular fitness.

• For contact sports, wear protective shoulder pads.

• Use proper sports technique.

Expected outcome

With appropriate repositioning of the joint (reduction) and immobilization for 3 to 6 weeks, healing of ligaments can be expected in 6 weeks. Repeated shoulder dislocations depend on the amount of trauma necessary to cause the first dislocation, age at the time of injury, and associated shoulder injury or bony defect. Recurrent dislocation is less common with posterior shoulder instability than after anterior dislocation. If customary treatment does not prevent a recurrence, athletic activities should be modified until surgery can be performed to cure the problem. Nonoperative treatment is successful in 70% to 90% of patients.

Possible complications

• Damage to nearby nerves or major blood vessels, causing temporary or permanent weakness, paralysis, numbness, coldness, and paleness

• Fracture or joint cartilage injury as a result of the dislocation or as a result of the reduction of the dislocation

• Prolonged healing or recurrent dislocation if activity is resumed too soon

• Rotator cuff tear

• Repeated shoulder dislocations, particularly if the previous dislocation is not healed completely or is not appropriately rehabilitated; most recurrent dislocations are caused by repeated injury.

• An unstable or arthritic shoulder following repeated injury or with associated fracture

General treatment considerations

After repositioning of the bones of the joint by trained medical personnel, treatment consists of ice and medications to relieve pain. Reduction usually can be performed without surgery, which may rarely be necessary to restore the joint to its normal position and to repair ligaments. Immobilization by brace, cast, or immobilizer for 6 to 8 weeks is recommended to protect the joint while the ligaments heal. After immobilization, stretching and strengthening of the stiff, injured, and weakened joint and surrounding muscles are necessary as a result of the injury and the immobilization. These may be done with or without the assistance of a physical therapist or athletic trainer. Nonoperative treatment provides relief in 70% to 90% of patients with posterior subluxation. Surgery is uncommonly recommended after the first dislocation to tighten the shoulder ligaments and repair the labrum, and it is usually reserved for those who have recurrent dislocations despite 6 months of appropriate rehabilitation. Surgery can be done arthroscopically, or it may be performed through a standard incision, although surgery is not as successful for posterior dislocations as it is for anterior dislocations.

Medication

• General anesthesia or muscle relaxers may be used to help make joint repositioning possible.

• Nonsteroidal antiinflammatory medications, such as aspirin and ibuprofen (do not take for 7 days before surgery), or other over-the-counter pain relievers, such as acetaminophen, are often recommended. Take these as directed by your physician, and contact your doctor immediately if any bleeding, stomach upset, or signs of an allergic reaction occur.

• Stronger pain relievers may be prescribed as necessary. Use these only as directed, and take only as much as you need.

Cold therapy

Cold is used to relieve pain and reduce inflammation. It should be applied for 10 to 15 minutes every 2 to 3 hours as needed after injury and immediately after any activity that aggravates your symptoms. Use ice packs or an ice massage.

When to call your doctor

• Pain, tenderness, or swelling worsens despite treatment.

• You have another dislocation.

• You experience pain, numbness, or coldness in your arm.

Figure 1

From Economou SG, Economou TS: Instructions for surgery patients, Philadelphia, 1998, W.B. Saunders, p 551.

• A blue, gray, or dusky color appears in your fingernails.

• New, unexplained symptoms develop. Drugs used in treatment may produce side effects.

Range of Motion and Stretching Exercises

Posterior Shoulder Instability

These are some of the initial exercises you may use to start your rehabilitation program, after your surgeon has said that you may begin moving your shoulder. The length of time your shoulder is immobilized, often 2 to 6 weeks, will vary depending on the type and severity of your injury. Continue these exercises as instructed, until you see your physician, physical therapist, or athletic trainer again, or until your symptoms resolve. Avoid motions that place your elbow all the way across the front of your body. Please remember:

• Flexible tissue is more tolerant of the stresses placed on it.

• A gentle stretching sensation should be felt.

Range of motion shoulder pendulum

1. Lean forward at the waist, letting your weak arm hang freely. Support yourself by placing your opposite hand on a chair, table, or counter as shown.

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