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Shoulder Instability / Shoulder Dislocations

Shoulder Instability web based movie

Overview

The shoulder is a “ball & socket” joint. The upper part of the arm bone (humerus) forms a ball shape that sits in a small cup, or socket (called the “glenoid”), on the side of the shoulder blade. The rim of the socket is surrounded by a ring of firm, rubbery cartilage called the labrum. The labrum functions to deepen the socket and to stabilize the ball in the socket. Shoulder read and layout as as the attachment site for ligaments that stabilize the shoulder joint.

Shoulder instability occurs when the ball of the arm bone slips either partially out of the socket (this is termed “subluxation”), or comes completely out of the socket (termed “dislocation”).

The two main causes of shoulder instability are:

  • Traumatic injury (decrease font and change from blue font)
  • Inherent looseness of the shoulder ligaments (also termed “laxity”) that worsens over time

Traumatic injury

A traumatic instability episode is the most common cause of instability. After the injury, the ball may slide back into the socket on its own (also called “reduced”), or may require medical treatment, usually in an emergency room, involving pain medication, sedation, and manual manipulation of the ball back into the socket. As a result of an instability episode (either subluxation or dislocation), a variety of structures in the shoulder may be damaged. Typically a tear of the labrum occurs (this tear is termed a “Bankart lesion”), and often the stabilizing ligaments of the shoulder are stretched to a certain degree. Additionally, on occasion a fracture of the bone of the ball and/or socket may occur. In older age patients (age >40), a tear of the rotator cuff may also occur.

Symptoms

In cases of shoulder instability due to looseness of the shoulder ligaments, there is usually no traumatic event that initiates problems in the shoulder. Many people inherently have looser ligaments in their joints and a higher degree of joint “laxity”, which is completely normal. However, repetitive stress on the shoulder from various activities (such as swimming, volleyball, or throwing) can further stretch ligaments. While most cases of shoulder instability after an injury lead to instability in one direction (termed “unidirectional instability”), instability due to loose or lax ligaments leads to instability in several directions, such out the front, back , and bottom of the shoulder joint (termed “multidirectional instability,” or “MDI”).

During an actual dislocation episode, the patient usually experiences severe pain. Often there is an obvious deformity in the shoulder region. Once the shoulder is reduced, the pain usually subsides significantly. Patients may notice numbness and tingling in parts of their hand or shoulder after a shoulder dislocation.

Once the initial pain from the injury subsides, many patients are able to gradually return to activities with no difficulties. Some patients, however, report apprehension or a sense of impending dislocation with the arm in certain positions. Other patients have episodes where the shoulder re-dislocates.

Symptoms of multidirectional instability are often more subtle. Patients can experience pain during sports or recreational activity with the arm in specific positions or motions. Often there is a dull ache in the shoulder during activity. There may or may not be a sensation of actual instability.

Diagnosis

The diagnosis of traumatic instability is made on based on the patient’s history and findings from a physical examination. The structural damage in the shoulder is then further defined by x-rays confirming reduction of the joint and presence of any fractures, particularly to the rim of the socket. A MRI scan may be performed looking for labral tears, stretching of the shoulder ligaments, and other associated injuries. In multidirectional instability, there is evidence of underlying joint laxity in other joints in the body, such as the elbow and finger joints. Pain is felt when the shoulder is stressed in the direction of instability. A MRI scan may be read as “normal” in cases of multidirection instability due to the subtly of the condition.

Treatment

The treatment of shoulder instability typically depends on the age and activity level of the patient as well as the number of instability episodes. Young patients (age <25), males, and those involved in collision/contact sports have a high rate of recurrent instability. For most patients after traumatic dislocation, non-operative treatment is recommended initially. This involves use of a sling with a short period of rest, followed by a course of physical therapy and a gradual return to normal activities. Patients with multidirectional instability are treated with physical therapy to strengthen the rotator cuff and other muscles that help stabilize the shoulder. Therapy exercises for MDI may take 3-6 months for full effect. Surgery is recommended in cases of repeated dislocation episodes, or if pain with use of the shoulder persists despite and adequate course of therapy exercises. The surgery is usually performed arthroscopically and may involve re-attachment of the torn labrum (termed “Bankart repair”) and/or tightening of stretched ligaments (termed “capsulorraphy” or “capsular plication”) .

Additional Information

For more information, visit
orthoinfo.aaos.org/topic.cfm?topic=A00035
orthoinfo.aaos.org/topic.cfm?topic=A00529
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