Shoulder Instability

rotator cuff painAnatomy

The shoulder joint consists of the humerus (arm bone), the glenoid (part of the scapula bone), the labrum, and the surrounding tendons and ligaments. The humeral head sitting in the glenoid can be thought of as a “golf ball on a tee” because of the large humeral head and small labrum.  As a result, the shoulder has a very large range of motion, but in exchange loses stability and is easily injured or dislocated. The four most important muscles and tendons that surround and stabilize the shoulder are the rotator cuff muscles: supraspinatus, infraspinatus, teres minor, and subscapularis. These muscles are covered by a bursa that helps lubricate the tendons and allow them to glide freely during motion.  Together, these muscles with the help of the labrum, a ring of cartilage around the glenoid, hold the humeral head into the shoulder “socket” and stabilize the shoulder. It is important to recognize that unlike other joints that have strong bone and ligament stabilizers, the shoulder is primarily stabilized by muscles and tendons.


Because the shoulder is relatively unstable, the humerus is at risk of dislocation or subluxation during activities – which is called shoulder instability. These symptoms are the result of deficiencies or weaknesses in the labrum, the glenoid, or shoulder capsule.  Sometimes, the weakness is the result of an injury, such as a shoulder dislocation.  In other cases, this may be result from stretching of the tissues over time. Often, this results from an initial injury, such as a dislocation, that becomes worse over time with repeated injuries and subluxation.

Shoulder dislocations can occur in any direction, but most commonly the humerus moves forward (anterior), which occurs during a throwing position. They may also compress and injury some of the nerves that pass in front of and underneath the shoulder joint, resulting in weakness and numbness over the outside of the arm.


The initial treatment for a shoulder dislocation or instability is reduction if the joint is dislocated. Your shoulder should then be immobilized in a sling or a brace for a period of time to let the swelling and pain decrease. Ice and rest is important during this period.  Once the pain and swelling go down, your doctor will prescribe a series of physical therapy exercises to regain your strength and motion.

In cases of chronic instability, when non-surgical treatment has not been able to relieve pain and improve symptoms, your surgeon may recommend a stabilization procedure. There are numerous options depending on your specific injury or limitation. This may include a capsule tightening, labral repairs, tendon or muscle transfers, and bone transfers. Speak with your surgeon to understand his or her preferred treatment options.


Your physician will recommend a specific rehabilitation protocol to enhance your recovery to activities and decrease pain after surgery. The importance of physical therapy in the shoulder cannot be overstated since it is the muscles and tendons that primarily stabilize the joint.  Exercises will consist of exercises for improving strength, maintaining motion, and re-training your muscles during the recovery phase. These exercises will typically progress in stages as the capsule and tendon heals and gets stronger. It is important to follow the protocol exactly as your surgeon recommends since going to fast may result in injury to the surgical repair and going too fast can result in stiffness and decreased motion. Exercises should be performed in a supervised setting, as well as at home on your own time. Your commitment to rehabilitation is key to a successful outcome.


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