The Shoulder joint is a ball and socket joint that connects the bone of the upper arm (upper arm) to the shoulder blade (scapula). The shallow socket in the scapula is glenoid. The capsule is a broad ligament that surrounds and stabilizes the joint. The glenoid labrum is thickened ring of cartilage circumferentially attached to the glenoid. If the arm is pulled or pushed out of its normal position in the socket, the capsule and labrum tear, usually away from the glenoid attachment point. A dislocation occurs when the humerus comes completely out of the socket and stays out. A subluxation occurs when the humerus comes partly out of the socket and then slips back in.
When the capsule tears from the glenoid rim, the shoulder can become unstable and dislocate or subluxate repeatedly. The most common direction for the humeral head to dislocate is toward the front of the body (anteriorly); this typically occurs if the arm goes too far behind the body when the arm is in an overhead position (such as when throwing a ball). The humeral head can also dislocate toward the back of the body (posterior); this occurs when the force to the arm is directed toward the back of the shoulder joint such as when falling forward on an outstretched arm or blocking with the arm straight ahead in football.
Diagnosis of Shoulder Instability
The direction of the shoulder dislocation or subluxation can usually be made by physical examination. It is possible for the shoulder to be unstable in more than one direction. Multidirectional instability is more common in loose-jointed individuals.
If the diagnosis of instability or direction is in doubt, additional tests that can be helpful are:
- MRI (magnetic resonance imaging)
- CT (computed tomography)
- Both of these radiographic tests can be performed after dye is injected into the shoulder joint (arthrogram).
- Examination under anesthesia followed by arthroscopy
Treatment of Shoulder Instability
Some patients who subluxate or dislocate their shoulder do well after the injury and do not have recurrent instability. They tend to be older in age and not active in sports, especially the overhead varieties. Young people, especially overhead athletes, are prone to have recurrent subluxations and/or dislocations and often need shoulder surgery to correct the shoulder problem (stabilization). The unstable shoulder joint can be repaired by reattaching the torn capsule and labrum to the glenoid rim. This is called a Labral Repair. The repair is generally done via arthroscopic surgery. In some instances, an open procedure is performed in which the muscles of the shoulder are separated to expose the shoulder capsule and underlying joint. Often the capsule tissue is also stretched loose and requires tightening with stitches, a procedure known as a capsuloraphy. This supplemental procedure can be done via the open as well as arthroscopic approach.
In either technique, the goal of surgery is to reattach the torn capsule and labrum to the glenoid rim allowing it to heal and to retighten the capsule back to its normal tension such that the shoulder joint is stabilized from subluxation and dislocation.
It takes several months for the capsule and labrum repairs to heal back to bone. During this time, extremes of shoulder motion and weighted stress must be avoided so that repairs are NOT damaged or undone.
Results and Risks of Surgery
The success rate of the open and arthroscopic repair are statistically equal ranging anywhere from 90-97%.
If there is fracture of the glenoid rim (Bankart lesion) and a compression fracture of the humeral head (Hill-Sachs lesion), there is an increased risk of recurrent instability following repair. Dependent upon the size of these injury related bone lesions, additional surgical procedures may be required for joint stabilization.
Two nerves are at risk during surgery as they are near the operative site; however, they are rarely injured.
As with any surgical procedure, there are always potential risks.
The incidence of infections is less than 0.5%.
The shoulder will become tight after surgery and will require extensive physical therapy to regain normal mobility. Occasionally, the shoulder can lose some overall motion after surgery; this is especially true if the shoulder has to be significantly tightened because of excess laxity and for severe injuries requiring extensive repairs.
Rarely, the shoulder may re-loosen over time causing recurrent laxity or instability; this is more so in the cases of non-traumatic instability rather than traumatic instability.