Introduction

Shoulder instability can be a common problem after a shoulder dislocation. Instability means that the shoulder is too loose and has a tendency to slip out of the socket (or glenoid). If the shoulder slips completely out of the socket, it has become dislocated. Repeated dislocations are not only a nuisance, but can cause further injury to the shoulder and can lead to arthritis of the shoulder if not treated.

The shoulder is made up of three bones: the scapula (shoulder blade), the humerus (upper arm bone) and the clavicle (collarbone).

The tendons of four muscles form the rotator cuff. Tendons attach muscles to bones. These muscles are called the supraspinatus, infraspinatus, teres minor, and subscapularis. Muscles move bones by pulling on tendons. When the rotator cuff muscles contract, they also hold the humerus tightly in the socket (glenoid) of the scapula. Strong rotator cuff muscles can help stabilize the shoulder.

The shoulder joint is completely surrounded by a bag of tissue that forms a watertight capsule around the joint. A series of ligaments join together to form this capsule.

A ligament is a soft structure made up of connective tissue. Ligaments attach bones to bones. The ligaments that make up the joint capsule have a considerable amount of slack, or looseness, so that the shoulder is unrestricted as it moves through its rather large range of motion. If the shoulder moves too far, the ligaments become tight and stop any further motion.

Sometimes the shoulder does not completely dislocate, but slips partially out and then returns to its normal position. This is called subluxation.

Ninety-seven percent of dislocations are anterior, meaning that the humerus slips out of the front of the shoulder socket. Only three percent dislocate posteriorly, or out the back.

Causes

Shoulder instability typically results from an injury that made the shoulder dislocate. This initial injury is usually serious enough to require that the shoulder be reduced, or put back into the socket, by a physician.

After the initial dislocation, the shoulder may remain unstable. The ligaments that are supposed to hold the shoulder in the socket may not heal properly, or they may remain stretched and too loose to keep the shoulder in the socket in certain positions. This can result in repeated episodes of dislocation, even during normal activities.

In some cases, instability may be present without an initial dislocation. The initial injury may not have been severe enough to cause a dislocation. Sometimes a genetic problem with the connective tissue of the body can lead to ligaments that are too elastic and stretch too easily. All the joints of the body may be too loose and some joints, such as the shoulder, may be easily dislocated. These people are sometimes referred to as double jointed.

Symptoms

A shoulder dislocation is usually obvious. The injury is very painful and the shoulder looks abnormal. Any movement is extremely painful.

A dislocated shoulder may cause damage to the nerves around the shoulder joint. If the nerves have been stretched, there will usually be a patch of numbness on the outside of the arm just below the shoulder. Several of the muscles around the shoulder may be slightly weak. This condition is usually temporary and will be corrected when the nerves recover.

Chronic instability causes several symptoms. The shoulder may slip, or sublux, in certain positions, such as when the hand is raised above the head in a throwing motion. Subluxation of the shoulder usually causes a quick feeling of pain, like something is slipping or pinching, in the shoulder.

The shoulder may become so loose that it dislocates frequently, severely restricting your ability to move.

Diagnosis

Correctly diagnosing shoulder instability depends upon knowing a history of your condition and performing a physical examination. For the dislocated shoulder, X-rays are necessary to rule out a fracture of the shoulder. X-rays are usually done after the shoulder is relocated to ensure it is back in place and no fractures are present.

For chronic instability, the diagnosis relies on a history of a dislocation (or confirmation by an X-ray) and a physical examination that suggests a loose shoulder. During the physical examination, your physician will stress the shoulder to test the ligaments. When the shoulder is stretched in certain directions, you may get the feeling that the shoulder is going to dislocate. This is a very important sign of instability and is called an apprehension sign. (Unless your shoulder is very loose, the shoulder will not dislocate during this test.)

In some cases where the diagnosis is in question, special tests, such as examining the shoulder while the patient is under general anesthesia or arthroscopy, may be suggested. This will allow the doctor to test the ligaments of the shoulder while the patient is asleep and the muscles around the shoulder are paralyzed.

Remember that the muscles play an important role in the stability of the shoulder, and it is sometimes difficult to test the ligaments alone if the patient is awake and tightening these muscles during the exam.

Treatment

The treatment of shoulder instability begins with a well-designed physical therapy program. The muscles and the ligaments around the shoulder add major stability. If the ligaments have been weakened by injury, the muscles can be strengthened to compensate to some extent. The important muscles are the rotator cuff muscles, since these are the muscles that pull the humerus into the socket when they are contracted. Most typical weight lifting programs do not focus on these muscles. Patients should consult a physical therapist for the proper exercises.

If rehabilitation fails to stabilize the shoulder, surgery may be suggested. Many types of shoulder operations are designed to stabilize the shoulder. Nearly all of these operations attempt to tighten the ligaments that are loose, usually the ligaments at the front of the shoulder.

One of the most popular methods for surgically stabilizing the shoulder that dislocates anteriorly (out the front) is a procedure known as a Bankart repair.

This procedure was developed based on the idea that the primary reason the shoulder is dislocating is that the ligaments in the front of the joint have been torn from their attachment on the front end of the socket (glenoid) of the shoulder joint. In this operation, the ligaments are sewn, or stapled, back into their original position and allowed to heal so that the shoulder is once again stable.

Typically, this operation is done through an incision at the front of the shoulder, but some physicians prefer to perform a similar operation with the aid of the arthroscope. This is a new technique and not yet widely practiced.