Arch Health Medical Group

Shoulder Instability

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Understanding Shoulder Instability

Your shoulder is made up of three bones: your upper arm bone (humerus), your shoulder blade (scapula), and your collarbone (clavicle).
 
The head, or ball, of your upper arm bone fits into a shallow socket in your shoulder blade. This socket is called the glenoid. Strong connective tissue, called the shoulder capsule, is the ligament system of the shoulder and keeps the head of the upper arm bone centered in the glenoid socket. This tissue covers the shoulder joint and attaches the upper end of the arm bone to the shoulder blade.
 
Your shoulder also relies on strong tendons and muscles to keep your shoulder stable.
 
Background
Shoulder dislocations can be partial, with the ball of the upper arm coming just partially out of the socket. This is called a subluxation. A complete dislocation means the ball comes all the way out of the socket.
 
Once the ligaments, tendons, and muscles around the shoulder become loose or torn, dislocations can occur repeatedly. Chronic shoulder instability is the persistent inability of these tissues to keep the arm centered in the shoulder socket.
 
Cause
There are three common ways that a shoulder can become unstable:

Shoulder Dislocation
 
Severe injury, or trauma, is often the cause of an initial shoulder dislocation. When the head of the humerus dislocates, the socket bone (glenoid) and the ligaments in the front of the shoulder are often injured. The torn ligament in the front of the shoulder is commonly called a Bankart lesion. A severe first dislocation can lead to continued dislocations, giving out, or a feeling of instability.


Repetitive Strain

Some people with shoulder instability have never had a dislocation. Most of these patients have looser ligaments in their shoulders. This increased looseness is sometimes just their normal anatomy. Sometimes, it is the result of repetitive overhead motion.
 
Swimming, tennis, and volleyball are some sports examples of repetitive overhead motion that can stretch out the shoulder ligaments. Many jobs also require repetitive overhead work.
Looser ligaments can make it hard to maintain shoulder stability. Repetitive or stressful activities can challenge a weakened shoulder. This can result in a painful, unstable shoulder.

Multi-directional Instability
 
In a small minority of patients, the shoulder can become unstable without a history of injury or repetitive strain. In such patients, the shoulder may feel loose or dislocate in multiple directions, meaning the ball may dislocate out the front, out the back, or out the bottom of the shoulder. This is called multi-directional instability. These patients have naturally loose ligaments throughout the body and may be "double-jointed."
 
Symptoms
Common symptoms of chronic shoulder instability include:

  • Pain caused by shoulder injury
  • Repeated shoulder dislocations
  • Repeated instances of the shoulder giving out
  • A persistent sensation of the shoulder feeling loose, slipping in and out of the joint, or just "hanging there"
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