Arthroscopic shoulder surgery for shoulder dislocation, subluxation, and instability: why, when and how it is done.

Edited By: Christopher J. Wahl, M.D., Suzanne L. Slaney, PA-C, ATC, MMS
Last updated Tuesday, January 25, 2005

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Review of the condition

Characteristics of shoulder dislocation, subluxation, and instability

By definition, all forms shoulder dislocation and shoulder instability share the common bond that the humeral head (or “ball” at the top of the arm bone or humerus) does not stay adequately centered on the glenoid (or “socket” attached to the shoulder blade). This instability can be subtle, manifesting as pain at the shoulder or upper arm with overhead activities; mild to moderate, manifesting as the inability to perform overhead activities without apprehension (or the sense that the shoulder could dislocate); or severe, in which the shoulder can easily dislocate voluntarily or involuntarily during any activities, overhead or otherwise. Figure 3 shows the humeral head dislocated from the glenoid socket (redrawn from Burkhart et al. Arthroscopy. 2000:16:7:682)

A dislocation following trauma (such as a sports injury or auto accident) may be obvious, requiring emergent relocation. However, subtle instabilities can be difficult to diagnose correctly in the hands of physicians who do not normally examine the shoulder. These are not infrequently misdiagnosed as “rotator cuff tears” or “bursitis”. In addition, shoulder instability can occur in concert with other shoulder problems, so if the instability is not recognized and treated, the results of a rotator cuff surgery or surgery to remove “bone spurs” may not alleviate the symptoms.

Most patients with significant instability will have the sense that the shoulder “feels like it could come out of joint” when in certain positions, or have the sense that the shoulder “pops out and in” frequently with activities.

Types

The wide range of problems that contribute to shoulder instability can be defined in several ways, including:

• SEVERITY: subtle, mild to moderate, severe (as described above)
• DIRECTION: anterior, posterior, multidirectional
• MECHANISM: traumatic or atraumatic

In fact, the severity, direction and mechanism all influence how the shoulder should best be treated, so all of these factors must be considered.

SEVERITY
In most cases of subtle, mild and moderate forms of shoulder instability, the surgeon may recommend an attempt to stabilize the shoulder through a physical therapy and strengthening program. A certain subset of individuals (contact athletes, overhead laborers, and people who have failed a trial of physical therapy) may require surgery.

Severe shoulder instability, manifested by frequent dislocations and subluxations during normal activities of daily living are less likely to resolve without surgery, but are also most difficult to treat. A subset of patients who may not improve with surgery are those who voluntarily or willfully dislocate their shoulders regularly, or those who are not willing or not able to undergo the appropriate postoperative rehabilitation.

MECHANISM
A shoulder dislocation in a previously “normal” shoulder after an accident, trauma, or a seizure may need to be relocated on an emergent basis in the emergency room. When this occurs, it is advisable that the patient seeks further medical attention with a qualified sports medicine or shoulder surgeon. In persons who have never had problems with the shoulder but then have a traumatic dislocation, a significant injury to the shoulder joint can occur that may result in recurrent episodes of instability or dislocation. Many times, the shoulder can be appropriately braced while it is healing to avoid the need for surgery.

Dislocations and subluxations can also occur in people without any inciting event. This is called atraumatic instability, and can be more difficult to treat. Many people who suffer from atraumatic instability are usually also “double jointed” or “ligamentously lax” in other joints. Because the shoulder is the joint in the human body with the largest range of motion (i.e. it is relatively less stable anyway), the extra laxity or give in the shoulder can predispose it to subluxation or dislocation.

DIRECTION
True dislocations most commonly occur to the front of the shoulder (or anterior dislocation), but can also be to the back (posterior dislocation), or in more than one direction (“multidirectional instability” or “MDI”).

The most common direction for dislocation and subluxation (instability) to occur is to the front of the shoulder (anterior dislocation). Anterior dislocations and subluxations are frequently associated with a disruption of the stabilizing ligaments at the front edge of the glenoid (this ligament tear is termed a “Bankart lesion”), but can occur in the absence of any discrete injury as well.

True posterior dislocations are rare, and are usually the result of seizures or major trauma. Posterior subluxation, however, can occur after repetitive athletic trauma, particularly in weight lifters and contact athletes in sports such as hockey, lacrosse, and football.

Persons who have atraumatic instability due to laxity of their shoulder ligaments may sublux or dislocate their shoulder in more than one direction; this is called “multidirectional instability” or “MDI”. Multidirectional instability is usually related more to an inherent elasticity in the connective tissues around the shoulder joint, and not to a discreet injury to any particular ligaments of the shoulder capsule. Physical therapy is the mainstay of treatment for mild multidirectional instability (MDI). More severe MDI may require surgery if a patient is to maintain an active lifestyle.

Similar conditions

Incidence and risk factors

The shoulder joint had the greatest range of motion of all the joints in the human body and every individual is unique in terms of the amount of ligamentous laxity (or flexibility) they have. For this reason, the “stability” of the shoulder joint is relative from person to person and shoulder to shoulder. In general terms, in the “normal” shoulder the humeral head (ball) should not travel more than a few millimeters in any direction from the center the glenoid (socket)—it should behave essentially as a “ball and socket joint”.

“Instability” of the shoulder joint should therefore be defined as excessive motion of the head away from the center of the socket (glenoid) that produces pain or the inability to perform activities of daily living, overhead motions, or sports. The same degree of movement causing symptoms in one person may be perfectly acceptable to another. It is therefore difficult to give an exact percentage of persons who suffer from any particular form of instability.

Once a young person (who is still growing) suffers a shoulder dislocation, it is statistically likely that they will dislocate again. Studies have shown that when a dislocation occurs in a child with open growth plates, there is up to a 100% chance that they will dislocate again. In young adults (after the growth plates begin closing but younger than 20 years old), the re-dislocation rate is about 55% to 95%. People who suffer their first dislocation after 30 or 40 years of age are much less likely to suffer another dislocation without a significant traumatic event (usually less than 10% to 15%). Unfortunately, older persons who dislocate their shoulders may develop other problems as a result of the dislocation, such as fractures at the joint or rotator cuff tears.

Risk factors for shoulder instability include:

• ligament laxity (“double jointed”)
• a history of previous subluxation/dislocation of the shoulder joint
• young persons (younger than 20 years old)
• overhead or throwing athletes (baseball, tennis)
• contact athletes (football, hockey, wrestling, lacrosse)

Diagnosis

A physician can diagnose shoulder instability by reviewing the patients history, performing a thorough physical examination and shoulder examination, and through the use of imaging techniques such as X-rays and magnetic resonance imaging (MRI).

The physical examination and history remain the most reliable means to diagnose instability, because several persons will have no abnormalities present on X-ray or MRI. X-rays may show bony injuries to the glenoid socket (termed a “bony Bankart lesion”) or to the humeral head (termed a “Hill-Sach’s lesion”). MRI may demonstrate tears of the stabilizing ligaments of the shoulder joint (termed “labral tears”, “capsular disruptions” or “soft tissue Bankart lesion”. Alternatively, the MRI may demonstrate an abnormally large or “loose” shoulder capsule (joint). Figure 4 shows an MRI of an unstable shoulder. The stabilizing ligaments are torn from the front of the glenoid (arrow). Figure 5 shows an arthroscopic view of the ligament attachments (L) the metal probe is on the labrum, where the ligament attaches. The top view is a normal attachment, the middle is a mild tear, below is a severely torn ligament attachment.

Medications

There are no medications that can treat the excess laxity or instability of the shoulder joint. However, some medications such as Non-Steroidal Anti-inflammatory Drugs (NSAIDs) will frequently help to ease pain or symptoms related to the unstable shoulder. These medications can be quite helpful, but can also have side effects and therefore should be taken under the supervision of a physician experienced in their use. Injections of steroids (cortisone) or lubricants (such as hyaluronic acid) into the shoulder have little role in the treatment of instability and carry some risk of infection.

For any medications taken, patients should learn:

• the risks, possible interactions with other drugs
• the recommended dosage
• the cost

Exercises

The stability of the shoulder joint is dependent upon a balance of several factors, including:

• the fit or conformity of the humeral head (“ball”) to the glenoid (“socket”)
• the integrity of the lip of tissue around the glenoid socket (also called the labrum)
• the integrity of the ligaments within the shoulder capsule that act as “check reigns” to motion (termed the glenohumeral ligaments)
• a “vacuum effect” of the head in the glenoid socket
• the stabilizing effect of the rotator cuff muscles around the shoulder joint

Of all these factors, the one that can be addressed most easily is the strength and function of the rotator cuff muscles. Frequently, the extra laxity of the shoulder joint capsule can be overcome by strengthening the muscles around the joint that are used to stabilize the humeral head in the glenoid socket. These muscles can be strengthened effectively with a supervised and home physical therapy program designed to selectively balance and strengthen the four muscles around the shoulder that comprise the “cuff” ( called the supraspinatus, infraspinatus, teres minor, subscapularis). Most general shoulder exercisers in the gym do not adequately isolate and address rotator cuff strengthening, so it is important to learn which exercises are most beneficial.

If the exercises are performed gently several times per day on an ongoing basis, many patients will obtain relief of their symptoms and suffer few or no episodes of instability. It is important for patients to learn the possible risks of physical therapy as well as its cost. The anticipated effectiveness of physical therapy is dependent upon the degree and nature of the instability.

Possible benefits of arthroscopic shoulder surgery

In persons who have recurrent episodes of shoulder subluxation or dislocation who continue to have instability despite an adequate trial of physical therapy, surgical stabilization of the shoulder is the most effective method to restore comfort and eliminate the symptoms.

A qualified shoulder surgeon can isolate the factors contributing to instability, including tears of the glenoid socket “lip” (or “labrum”), tears of the shoulder capsule and ligaments, bony fractures of the glenoid socket or humeral head, the integrity of the rotator cuff tendons, or excessive laxity or volume of the shoulder capsule. Video 2 shows a short “diagnostic arthroscopy” of the shoulder, a virtual tour around the joint. This person has a normal glenohumeral ligament attachment, but a partial-thickness rotator cuff tear. Video 3 shows the “diagnostic arthroscopy” in which the ligament attachments at the front of the shoulder are torn. There are different procedures to address each of these problems, and most can be done on an outpatient basis using the arthroscope and special instruments designed to be used through very small incisions (3 to 4 incisions about 1-cm long). Note: Videos may be slow to load on non-broadband internet connections. Modem users may wish to right click (or Command click for Macs) and save the file locally for viewing.

The overwhelming majority of patients who undergo arthroscopic shoulder surgery to address shoulder instability will have a successful result without recurrent problems with subluxation, dislocation, or pain.

Links

• Video 2 - A short “diagnostic arthroscopy” of the shoulder
• Video 3 - The “diagnostic arthroscopy” in which the ligament attachments at the front of the shoulder are torn

Surgery for shoulder dislocation, subluxation, and instability at the University of Washington

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