Shoulder instability refers to inability of the humerus (ball part of the shoulder joint) to stay centered in the socket (glenoid) following a shoulder dislocation event. This should not be confused with a “shoulder separation,” which refers to an injury that causes the collarbone to separate from the shoulder blade.
Normal shoulder stability requires a complex interplay between bony and soft tissue stabilizing structures. The natural shape of the shoulder joint allows for a wide arc of motion, and therefore only provides a limited amount of inherent stability. As a result, the shoulder relies on soft tissue structures, including the capsule, labrum and glenohumeral ligaments, as well as muscles of the rotator cuff, to maintain stability.
What are some common ways the shoulder can become unstable?
During a dislocation event, the soft tissue stabilizers of the shoulder are injured. These include the capsule, ligaments and labrum, which is the fibrous cartilage attachment of the capsule on the rim of the socket. Injury to these structures alters the soft tissue balance of the shoulder and often results in recurrent dislocations or the sensation that the shoulder is unstable (apprehension). Several studies have found that age of the patient at time of injury will influence the chance of having continued shoulder instability (recurrent). Patients who are the most likely to have recurrent instability include patients under the age of 25, males, and athletes who compete in contact sports. Recurrent instability events increase the chance of damaging the bone of the glenoid, as well as placing the rotator cuff and crossing nerves at risk for injury.
What are the symptoms associated with shoulder instability?
People who have recurrent instability complain of a fear of the shoulder coming out of socket, which is typically associated with pain and weakness. The shoulder may intermittently come partially or completely out of socket. Patients may report apprehension with using their arm because they feel as if the shoulder will fall out of socket.
How does the shoulder dislocate?
The most common direction of dislocation is anterior, where the humerus dislocates out of the front part of the glenoid. Patients with anterior shoulder instability usually have apprehension with the arm in the throwing position. Patients with the opposite problem, posterior instability, will feel apprehensive or may sustain a dislocation with the arm in the forward and inwardly rotated position (thumb pointed towards the floor). Patients with so-called multidirectional instability may feel that the shoulder is apprehensive in many different positions. These patients will often have other signs of hyperlaxity, or too much motion of the shoulder and other joints (fingers, wrist, and elbows) compared to other people with “normal” shoulders. Typically these patients have been told they are “double-jointed,” which refers to laxity in their joints.
What treatment options are available for patients suffering from shoulder instability?
For most patients, an initial dislocation can be treated with a sling for a short period of time followed by focused physical therapy. If the patient continues to have pain or other episodes of instability, surgery may be considered. The most common surgery involves repair of the labrum and the capsule to the edge of the glenoid to restore its anatomic position and tension. Most commonly, this is done with an arthroscopic approach, which involves several small incisions and using a camera in the shoulder joint to visualize the problem and using small instruments to perform the repair.
Occasionally a dislocation of the ball over the front of the socket can be associated with a bony fracture. These patients may require an open surgery to correct this bone defect with a “Latarjet procedure.” The Latarjet procedure uses the coracoid process of the scapula as a bone graft to reform the front of the socket where the bone is deficient.
The transferred bone is placed via a split in the front rotator cuff muscle, the subscapularis. A strong pair of tendons, including the short head of the biceps, is attached to this transferred bone. When the arm is brought into the throwing position (a usual position of instability) the lower subscapularis acts as a tether, keeping the shoulder from moving forward. The biceps tendon acts as a second barrier, helping to also keep the shoulder from dislocating with a so-called “sling effect.” Ultimately, the Latarjet procedure can be an effective procedure for treating patients in whom previous soft tissue repairs have failed.
What can patients expect following treatment for shoulder instability?
After surgery, you can expect to be in a sling for about four weeks. Therapy is then initiated as a gradual progression of motion and strengthening of the structures that help hold the shoulder in position, including the rotator cuff and muscles that attach and position the shoulder blade. Ultimately, it will take four to five months before patients have cleared all restrictions and can get back to most activities.