The shoulder is a ball and socket joint, with the humeral head as the ball and the glenoid as the socket. Instability occurs when the ball slips out of the socket, through dislocations or partial dislocations (subluxation). Because the shoulder has such a great range of motion, it can even experience instability in multiple directions (anteriorly, posteriorly, and in multiple directions).
A variety of tissues keep the shoulder in place, including a capsule, labrum, ligaments, tendons, and muscles. An injury to any of these structures can contribute to shoulder instability.
Previous dislocation, labral tears, genetics, repetitive strain, and multidirectional instability can lead to shoulder instability. Repetitive strain can cause damage to the labrum, capsule, rotator cuff, deltoid, biceps tendon or ligaments within the shoulder leading to instability.
At-risk populations for shoulder instability include individuals with very loose joints or connective tissue diseases, as well as athletes who participate in repetitive overhead activity (baseball, swimming, and volleyball). Injuries to the above shoulder stabilizers can increase an athlete's risk of instability.
Signs and symptoms
The most common symptoms of instability are activity related pain, decreased strength and performance. Athletes with shoulder instability may experience frequent subluxations or dislocations. Other common symptoms of instability include pain when carrying heavy objects, such as a suitcase, or apprehension in certain positions on physical examination. Bruising, swelling, pain and reduced range of motion may also be present.
Shoulder instability is typically diagnosed through a thorough history and physical examination. Diagnostic imaging tests like X-Rays, MRIs, and CT scans can also aid in the diagnosis of shoulder instability and associated injuries.
The initial treatment for shoulder instability includes rest, ice, NSAIDs, avoiding aggravating activities, and immobilizing the joint via a sling or brace. After this, physical therapy exercises to increase strength and range of motion in the shoulder can help increase stability.
If these options are unsuccessful, surgery can be performed via arthroscopy, or open surgery (in more severe cases).
If the athlete has experienced a traumatic dislocation or recurrent subluxations/dislocations they may also have associated fractures or labral tears that need further management as well.