Shoulder Instability

By Dr. Bruce Blackstone, M.D.

The term shoulder instability encompasses a spectrum of conditions and symptoms. The most dramatic and painful variety is acute traumatic dislocation of the shoulder in which the humeral head comes completely out of the socket, whereas, the opposite end of the spectrum is chronic subluxation manifested only by pain with overhead use of the arm.

The shoulder has the greatest range of motion of any joint in the body. In general, the normal shoulder allows just a few millimeters of movement of the humeral head away from the middle of the socket, a term called translation. Every individual is different, however, regarding the amount of flexibility or ligamentous laxity they have. Movement that is painfully disabling in one person may be perfectly well tolerated by another. Therefore, the term instability doesn’t just refer to degrees of flexibility but to symptomatic, abnormal translation of the humeral head with respect to the socket.

Given the motion requirements of the shoulder, stability of this joint depends on many factors all balanced in a finely tuned manner. These include the conforming fit of the ball shaped humeral head into the shallow cup shaped socket, the integrity of the labrum, which is the tough lip of tissue which surrounds and deepens the socket, the integrity of the capsular ligaments that restrict extremes of motion and the secondary stabilizing effect of the rotator cuff muscles that surround the joint.

Violent trauma to the shoulder, such as experienced in a motor vehicle accident, fall from a height, or other forms of wrenching force to the shoulder as are often experienced in athletic injuries, may cause the shoulder to completely dislocate, i.e., come out of the socket. A great majority of these are anterior dislocations, i.e., the head “pops out” in front of the socket. In so doing, the most common structures injured are the anterior labrum and the adjacent capsular ligaments. Occasionally, a fragment of bone may fracture off the leading edge of the socket and the back portion of the humeral head frequently sustains a compression fracture (Hill-Sachs defect), where the dislocated head abuts against the edge of the socket.

Labrum (left) torn away from socket

Hill-Sachs defect of humeral head

A first time dislocation is typically very painful and requires a medical professional to reduce the shoulder, i.e., put the shoulder back in the socket. Often the injured structures heal adequately with time and rest, such that recurrent instability is not a problem. This is likely the case in those over forty years of age. However, recurrent instability is seen much more frequently in younger individuals. In fact, the likelihood of recurrent dislocation may exceed 80% to 90% in those under twenty years of age at the time of the first episodes and, in the skeletally immature, even higher recurrence rates are seen, i.e., approaching 100%.

Recurrent instability can manifest itself as repeated dislocation or subluxation (partial dislocations, usually spontaneously or self reduced, or a feeling of apprehension or pain with reaching upward or outward). This chronic, recurrent instability can significantly alter ones lifestyle and, in the case of athletes, can drastically interfere with one’s ability to continue participation. Recurrent dislocations are painful and can cause more damage to the joint surfaces and surrounding soft tissues, possibility leading to significant arthritic changes.

DIAGNOSIS

Repeated dislocations that require reduction make the diagnosis of recurrent instability fairly obvious. More often than note, however, the proper diagnosis requires a careful combination of history, physical exam, and imaging. Your orthopedic physician can sort out history and physical exam findings that distinguish instability from other shoulder conditions. Imaging techniques include plain radiographs, MRI, and sometimes CT scans. Plain radiographs can show glenoid rim fractures and Hill-Sachs compression fractures of the posterior aspect of the humeral head. MRI is used to diagnose labral tears, capsular tears or stretching and SLAP tears (tearing of the attachment of the biceps to the superior glenoid labrum). CT is sometimes used to confirm the extent of bone defects in the humeral head and glenoid. None of these techniques are foolproof and a complete diagnosis oftentimes depends also on exam under anesthesia and diagnostic arthroscopy.

Dislocated right shoulder

Dislocated right shoulder - radiograph

TREATMENT

Not infrequently, cases of mild instability may respond favorably to a course of physical therapy concentrating on shoulder muscle rehabilitation. Strengthening and toning of the rotator cuff and periscapular muscles can provide stability to an otherwise mildly unstable shoulder.

More often, however, instability of the shoulder may prove to be a hindrance to participation in sports or overhead activities or even make the performance of routine activities of daily living difficult despite a diligent attempt at nonoperative treatment. Assuming the patient does not voluntarily dislocate the shoulder and he or she is capable of and willing to actively participate in a structured postoperative physical therapy program, surgery to stabilize the shoulder may then be recommended. Surgery for instability of the shoulder usually involves repair of the labrum and/or capsular ligaments to the glenoid rim or a generalized tightening of the shoulder capsule.

These procedures can be done via standard “open surgery” through a significant incision or arthroscopically through a few very small incisions. Through the years, the “gold standard” has been the open Bankart repair (repair of labrum and capsule to the glenoid rim) or the open capsular shift for MDI (multidirectional instability). In the past few years, the success rate of the arthroscopic Bankart repair for the treatment of traumatic anterior instability has equaled that of the open procedure, approximately 90% to 95%. Given this high success rate and several advantages of the arthroscopic technique over the open procedures, the arthroscopic Bankart repair for an increasing number of surgeons has become the procedure choice for the treatment of traumatic instability of the shoulder. Arthroscopic capsulorraphy or capsular tightening for MDI has show very excellent results with similar advantages as well.

Advantages of the arthroscopic approach include less tissue dissection for the surgical approach and, therefore, usually less pain postoperatively. Also, stabilization of the joint while maintaining close to normal range of motion is easier with the arthroscopic approach because the subscapularis tendon in the front of the shoulder is not violated as it typically is in the open approach. This is especially important in throwing athletes.

The main advantage to the arthroscopic approach is much better visualization of associated pathology in the rest of the shoulder joint, such as superior labral tears (SLAP tears) near the biceps origin or posterior labral tears, articular cartilage lesions and additional capsular lesions. As such, a more comprehensive and accurate diagnosis of the problem and treatment of the pathology can often be accomplished arthroscopically.

One situation in which an open procedure is clearly indicated is that of significant glenoid or humeral head bone loss. Anterior glenoid bone loss resulting in an inverted pear shape to the socket or large engaging Hill-Sachs defects of the humeral head typically require open procedures, such as coracoid transfers or other bone grafting procedures as well as soft tissue reconstruction.

THE PROCEDURE

After appropriate anesthesia and with the patient completely relaxed, the surgeon first examines the patient’s shoulders, comparing the symptomatic shoulder with the opposite shoulder. The degree and direction of translation of the head with respect to the socket are determined. Also, any abnormal crepitance or grinding sensations are noted. The exam under anesthesia typically confirms the surgeon’s diagnosis made preoperatively but occasionally unexpected findings may influence the treatment provided.

Most often, the next step is arthroscopic evaluation of the joint. This step, called diagnostic arthroscopy, involves placing one or two 1 centimeter skin incisions around the shoulder, through which special small instruments are inserted in the shoulder. An arthroscope is a rod shaped instrument approximately 5 millimeters in diameter with a lens on either end connected by fiber optics. One end is inserted into the shoulder and the other is connected to a camera, which allows the surgeon to view the interior contents of the shoulder on a video monitor. A probe or other small instruments can be used through the other portal (incision) to help assess the status of all pertinent structures inside the joint, such as the labrum, capsular ligaments, articular surfaces, biceps origin and rotator cuff tendons.

Once the pathology is defined, the surgeon can decide upon the best approach to repair or reconstruct the shoulder. Open and arthroscopic surgery are different techniques utilized to accomplish the same thing, i.e., repair of injured tissues. For the most common type of shoulder instability, traumatic anterior instability, arthroscopic repair, because of its high success rate and the need for less tissue dissection than an open surgery, is often the procedure of choice.

One or two additional portals are made into which hollow cannulas are placed, which allow instruments and implants to be freely placed into the shoulder. Suture anchors, absorbable threaded devices to which sutures are attached, are placed in the rim of the socket. The attached sutures are then passed through the torn labral or capsular tissues allowing them to be tightened or repaired back to the socket rim.

Uncommonly, the unstable shoulder will be found to be loose in several directions (MDI). This type of instability can be addressed arthroscopically as well, although, depending on a variety of factors, may often best be treated with an open “capsular shift.” Similarly, significant glenoid or humeral head bone loss may make an arthroscopic approach to the repair unsuitable.

Labrum torn away from socket

Suture anchor placed in rim of socket

Labrum repaired

AFTER SURGERY

After surgery, the repaired structures must be protected adequately to allow healing. Some early range of motion after repair is important but unrestricted range of motion can endanger the success of the procedure. Typically, a sling is worn for three to six weeks as an aid to the patient and reminder to others that the patient’s shoulder needs protection. No significant lifting or carrying with the extremity is allowed and the shoulder is protected from external rotation/abduction forces (i.e., reaching outwards and upwards). At approximately six weeks, formal physical therapy concentrating on gradually regaining range of motion is instituted followed by shoulder girdle strengthening exercises. Formal physical therapy sessions that allow close supervision by a well-trained therapist are very important as is a home exercise program designed by your therapist and surgeon. Typically, twelve to sixteen weeks are required to comfortably and safely return to unrestricted activities of daily living and it is preferable to avoid collision sports for six months post surgery and even this is assuming compliance with a dedicated rehabilitation program.