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The shoulder is a ball-and-socket joint with a wide range of motion. That impressive range of mobility also makes the shoulder quite unstable, however.

Damage to one or more of the structures that work together to stabilize the shoulder can result in shoulder instability. Those structures include:

  • 4 "rotator cuff" muscles
  • the fibrous joint capsule
  • the labrum, a ring of tissue that lines the socket area, and
  • ligaments, which connect bone to bone.

An unstable shoulder allows the ball-shaped top of the upper arm bone (humerus) to move about excessively in the socket (glenoid). Instability can lead to shoulder dislocations and damages to the structures in the joint. These conditions can reduce your ability to work, exercise and perform self-care activities.

Causes
Injury is the No. 1 cause of shoulder instability. Falling on your shoulder or outstretched hand, or sustaining a strong blow to the shoulder by an object or another person can tear muscles or ligaments. In some people, shoulder instability is hereditary - they experience joint laxity throughout their bodies. Work and recreational activities that involve a great deal of shoulder motion can also overstress the joint.

Symptoms
Signs of shoulder instability may appear suddenly, or may develop over time. They will vary according to the degree of instability. You will experience some pain and swelling in the area, and partial-to-complete loss of shoulder movement. The upper arm bone may pop in and out of place. A bone moving partially out of the joint is known as a subluxation. A dislocation occurs if the bone moves completely out of the joint.

Diagnosis
Your doctor will ask questions about your symptoms and the history of the problem. A physical examination of the shoulder and its movement will help identify signs of instability. And X-rays may be taken to assess joint alignment and rule out the possibility of broken bones. An MRI (magnetic resonance imaging) may be used to identify any detached ligaments.

Treatment
Conservative treatment consists of a period of rest and immobilization of the affected shoulder. For dislocations, the shoulder may be manually repositioned into place. You may need to wear a sling to support the joint and allow soft tissue to heal. Anti-inflammatories may be recommended to decrease pain and swelling. And ice packs may be applied to the area several times a day until the swelling disappears.

Severe or recurrent cases may require surgery, also known as shoulder stabilization. This procedure allows your doctor to repair the damaged tissues and restore stability to the shoulder joint. As with conservative treatment, a period of rest and rehabilitation will follow the surgery.

A rehabilitation program guided by a physical and/or occupational therapist may be recommended by your doctor. The goal of rehab is to help you return to regular activities and restore function in the shoulder.

Recuperation
The time necessary for your shoulder to heal will depend on your age, overall health, extent of the instability and the treatment recommended by your doctor. Patients with mild conditions may require just a few weeks to regain strength and flexibility. Cases requiring surgery may need 4-6 months for complete recovery. Following your rehabilitation program as closely as possible will promote healing and help prevent re-injury.