The normal shoulder is a marvel of mobility and stability. It provides more motion than any other joint in the human body yet the humeral head (ball of the shoulder joint) remains precisely centered in the glenoid (the socket of the joint) throughout the wide range of shoulder activities. One of the main stabilizing mechanisms is concavity compression in which the head of the humerus is held into the glenoid concavity by the action of the rotator cuff (much like a golf ball is held into the concavity of a golf tee).
The figure shows the humeral head the glenoid and one of the muscles of the rotator cuff. The concavity of the shoulder socket is deepened by a fibrous ring known as the glenoid labrum (see movie 1). The glenoid labrum greatly increases the stability of the shoulder (see movies 2 and 3). Another stabilizing mechanism is ligament restraint in which the motion of the shoulder is kept within the proper range by ligaments that span the joint (see movie 4).
The glenoid labrum and the ligaments can be torn when the arm is forced backwards allowing the humeral head to dislocate from the glenoid. If the labrum and the ligaments do not heal the shoulder may continue to be unstable allowing the ball to slip from the center of the glenoid even with minimal force.
When recurrent shoulder dislocations or feeling of instability interfere with the comfort and security of the shoulder a repair of the ligaments and labrum by an experienced shoulder surgeon can usually restore the stability of the joint.
The patient with an unstable shoulder requires a thorough history and physical examination along with proper x-rays.
The most common form of ligament injury is the Bankart lesion in which the ligaments are torn from the front of the socket. A solid surgical repair requires that the torn tissue be sewn back to the rim of the socket. Failure to secure this lesion solidly can result in failure of the repair.
If the glenoid bone is deficient the shoulder may benefit from a surgery to restore the lost bony anatomy.
Symptoms & Diagnosis
Characteristics of shoulder dislocations
Instability is a common cause of shoulder injury; shoulder function can usually be improved by a surgical repair. Individuals with shoulder instability usually notice that the shoulder feels unsteady or the ball may actually slip out of the joint in certain positions such as when the arm is out to the side or across the body. People with anterior (frontward) instability of the shoulder have difficulty throwing because this action depends on normal ligaments across the front of the joint as shown in the figure and movie 5.
The most common type of shoulder instability is traumatic anterior instability. In this type the ligaments and the labrum at the lower front part of the shoulder are torn by an injury that occurred when the arm was out to the side.
The figure on the left shows in cross section the capsule and labrum torn from the edge of the glenoid socket. Note that the damaged socket resembles a golf tee with one of its edges broken away so that the golf ball will tend to roll off of it. The figure on the right shows the same injury looking at the socket with the ball removed. The gap between the glenoid and the torn capsule and labrum is where the ball dislocates. The tear of the labrum and capsule from the glenoid is called a "Bankart Lesion".
Common causes of this injury include a skiing fall with the arm out to the side a clothesline tackle or a blocked spike in volleyball. The shoulder may not pop back in the joint but instead often needs to be put back in place by experienced assistance such as in an emergency room. The dislocated shoulder is given a chance to heal; then the patient is started on a rehabilitation program.
Not infrequently the labrum and the ligaments do not heal completely and the shoulder continues to feel unsteady (for example when the arm is moved out to the side and backward). These injuries seriously compromise the stability of the shoulder. An unhealed Bankart Lesion can result in recurrent anterior shoulder instability. When multiple dislocations have occurred the chances of healing without surgery become small.
A similar type of injury can occur to the back of the joint (traumatic posterior shoulder instability) but it is much less common. Traumatic posterior instability arises from mechanisms such as a fall on the outstretched hand.
There is another type of instability which arises without an injury--atraumatic instability. In this condition the shoulder loses its normal ability to center the ball in the glenoid socket. Not infrequently atraumatic instability may allow the shoulder to slip in different directions (multidirectional instability). In this condition there is usually nothing torn but rather the stabilizing structures of the shoulder decompensate.
Shoulder instability must be distinguished from other causes of shoulder dysfunction such as arthritis rotator cuff tear and snapping scapula. Arthritis usually results in shoulder stiffness and pain; X-rays show the loss of the joint space. Rotator cuff tear results in shoulder weakness. In snapping scapula the shoulder pops when the shoulder blade is moved on the chest wall.
Shoulder dislocations are among the most common conditions of the shoulder. They are more likely to be found in people from 15 to 35 years of age. Individuals over the age of 40 who dislocate their shoulders are likely to also have a tear of the rotator cuff. Those who have instability of one shoulder are somewhat more likely to have instability of the opposite shoulder. People with loose joints are more likely to have atraumatic instability.
Medications cannot help the healing of a torn labrum or ligament. Mild pain-relieving medications can be used to make shoulders with instability more comfortable.
Shoulder exercises to strengthen the rotator cuff such as those shown in the figure above may help control an unstable shoulder. Particularly in atraumatic instability rotator cuff strengthening and training the shoulder for stability are the mainstays of treatment.
In traumatic instability the repair of the labrum and the ligaments can usually restore stability to the joint. The restoration of stability often allows patients to return to their usual activities.
In atraumatic instability there is no single lesion to repair. Thus if exercises do not restore joint stability careful consideration needs to be given to the advisability of any surgical procedure. While tightening or burning the ligaments and capsule of the joint have been used for this condition it is recognized that these procedures may not specifically address the cause of the instability.
Possible benefits of surgical repair for shoulder dislocations
The effectiveness of any surgical procedure depends on the health and motivation of the patient the condition of the shoulder and the expertise of the surgeon. When performed by an experienced surgeon surgery for shoulder instability usually leads to improved shoulder comfort and function. This is particularly the case for individuals with traumatic instability where the injury can be specifically repaired. The greatest improvements are in the ability of the patient to sleep to perform activities of daily living and to engage in recreational activities.
Goal of surgery
Surgery to repair instability can help restore the function and comfort of unstable and dislocating shoulders. The goal of surgery for traumatic anterior instability is to repair the ligaments and the labrum that are torn from the lower front part of the glenoid socket. The opportunity for a secure and anatomic repair is best when the repair is done through open (not arthroscopic) surgery. As shown in the figure the incision is made in the normal skin creases around the shoulder leaving a minimal surgical scar.
Surgery for traumatic vs. atraumatic instability
Figure 6 shows how ligaments and the labrum can be anatomically repaired so that their function is restored. If there is a substantial loss of the bone of the anterior glenoid lip this can be restored by fixing a bone graft from the iliac crest (hip bone at the belt line) outside the shoulder joint capsule.
When performed by an experienced shoulder surgeon surgery for traumatic anterior instability has an excellent chance of restoring stability to the shoulder.
For traumatic posterior instability a similar repair can be carried out through an incision over the back of the shoulder.
For atraumatic instability exercises are the first choice in treatment. When these are not successful the surgical approach needs to be tailored to the specific circumstances. If the primary direction of atraumatic instability is posterior a posterior glenoid osteoplasty provides a robust reconfiguration of the shape of the glenoid so that it provides additional stability. For multidirectional instability a procedure to build up the glenoid labrum may increase the effective concavity of the glenoid socket. For patients with ligamentous hyperlaxity (excessive range of motion of the shoulder) a ligament and capsule tightening procedure is considered. This has been done with open surgery (known as a capsular shift) and by arthroscopic surgery (for example by burning and scarring the capsule).
Who should consider surgical repair for shoulder dislocations?
Surgery is considered for patients with:
What happens without surgery?
For traumatic anterior shoulder instability the most dependable results have been obtained with an open (not arthroscopic) repair that securely restores the attachment of the labrum and the ligaments to the edge of the glenoid socket as shown in the figure.
While arthroscopic approaches to surgical repair have been developed the chance of persistent instability is less when the repair is carried out by open surgery. This may be due to the increased difficulty in restoring the normal anatomy and in achieving a secure repair using arthroscopic surgery. The return to activities after open surgery is at least as fast as with arthroscopic repair. The cosmetic appearance of the shoulder after open surgery done through the natural skin creases is at least as good as that after arthroscopic repair. For shoulders in which the bone of the anterior (front) lip of the glenoid socket is lacking bone grafting can be used to restore the configuration of the socket.
For shoulders in which the back of the socket is too flat a reshaping of the socket (posterior glenoid osteoplasty) can be used.
For shoulders in which the soft tissues provide insufficient stability to the shoulder procedures can be considered to tighten the ligaments and capsule and to thicken the glenoid labrum (the "O" ring that surrounds the surface of the socket).
In the hands of an experienced surgeon repair for recurrent traumatic instability has an excellent chance of restoring much of the lost comfort and function to the unstable shoulder. With a good rehabilitation effort and with the avoidance of additional injuries the result of the surgery should last for a long time.
The results of surgery for the more unusual types of instability depend on the specifics of the shoulder problem and the type of surgery performed. Patients should discuss the details of the problem and the proposed procedure with the surgeon.
Surgery for instability is not an emergency. Such a repair is an elective procedure that can be scheduled when circumstances are optimal. The patient has time to become informed and to select an experienced surgeon.
Before surgery is undertaken the patient needs to:
1. be in optimal health
2. understand and accept the risks and alternatives of surgery and
3. understand the post operative rehabilitation program.
Surgery for shoulder instability should be performed when conditions are optimal. Particularly in the case of atraumatic instability an extended effort at non-operative management is suggested. This is because there is not a specific surgical repair for a specific injury. On the other hand in the case of recurrent instability or apprehension after an injury surgery can be performed whenever it becomes evident that exercises are not effective in restoring the shoulder's ability to function. Usually a 6- to 12-week try at strengthening exercises is sufficient to determine whether exercises are likely to be effective.
The risks of surgery for shoulder instability include but are not limited to the following:
There are also risks associated with anesthesia including death. An experienced shoulder surgery team will use special techniques to minimize these risks but cannot totally eliminate them.