The shoulder is a complex, ball-and-socket joint that rotates through a greater range of motion than any other joint in the body. The shoulder is made up of: the upper arm bone (humerus), shoulder blade (scapula), and collarbone (clavicle). The ball, or head of the upper arm, fits into a shallow socket (glenoid) in the shoulder blade. The ends of these bones, where they touch, are covered with articular cartilage, a smooth substance that protects the bones and enables them to move easily. The glenoid is ringed by the labrum, a strong, fibrous cartilage that forms a gasket around the socket, adding stability and cushioning the joint.
The shoulder joint is surrounded by bands of tissue, called ligaments, to form a capsule that holds the joint together. The undersurface of the shoulder capsule is lined by the synovium, a thin membrane that produces synovial fluid to lubricate the cartilage and eliminate friction. Four tendons surround the shoulder capsule and help keep the arm bone centered in the shoulder socket. This thick tendon material, called the rotator cuff, covers the head of the humerus and attaches it to your shoulder blade. Between the rotator cuff and the bone on top of your shoulder (acromion), a lubricating sac (bursa) helps the rotator cuff tendons glide smoothly during movement.
Normally, these components work together in harmony, but when disrupted by disease or injury the result can be pain, muscle weakness and reduced function.
Although the enables you to lift your arm, turn or rotate it in many directions, and reach above your head, this greater range of motion also results in less stability. Shoulder instability occurs when the head of the upper arm bone is forced out of the shoulder socket due to sudden injury or overuse. In a partial shoulder dislocation (called a subluxation), the ball of the upper arm only comes partially out of the socket, but in a complete dislocation the ball comes all the way out of the socket.
Once a shoulder has dislocated, or the shoulder's ligaments, tendons and muscles become loose or torn, that shoulder is vulnerable to repeated dislocations. Chronic shoulder instability is the persistent inability of these tissues to keep the arm centered in the shoulder socket, so the shoulder is loose and slips out of place repeatedly.
There are three common ways that a shoulder can become unstable.
Common symptoms of chronic shoulder instability include: pain caused by shoulder injury, repeated shoulder dislocations, repeated instances of the shoulder giving out, or a persistent sensation of the shoulder feeling loose, slipping in and out of the joint, or just "hanging there."
During an examination of your shoulder, your doctor may check for general looseness in your ligaments and perform specific tests to assess instability in your shoulder. Imaging tests may be needed to help your doctor confirm your diagnosis and identify any additional problems.
Chronic shoulder instability is often first treated with nonsurgical options. Your doctor will develop a treatment plan to relieve your symptoms. It may take several months of nonsurgical treatment before you can tell how well it is working. Nonsurgical treatment typically includes:
If nonsurgical options do not relieve the pain and instability, surgical repair may be necessary to enable the torn or stretched ligaments to hold the shoulder joint in place. For some patients, shoulder arthroscopy (minimally invasive surgery) may be appropriate, while others may require traditional open surgery. Your orthopaedic surgeon will discuss the options with you and recommend the procedure that meets your individual health needs.
It is important that you follow your doctor's treatment plan carefully. After surgery, your shoulder may be immobilized with a sling for several weeks, depending on your condition. Once your orthopaedic surgeon has removed the sling, you will be given specific program of physical therapy to help you improve the range of motion in your shoulder and prevent scarring. As the ligament heals, exercises to strengthen your shoulder will be gradually added. Rehabilitation plays a vital role in getting you back to your daily activities. The process may seem slow, but your commitment to physical therapy is key to experiencing a successful outcome.