Injuries to the Glenoid Labrum
A Diagnostic and Treatment Challenge
David B. Richards, MD
THE PHYSICIAN AND SPORTSMEDICINE - VOL 27 - NO. 6 - JUNE 1999
In Brief: The glenoid labrum contributes to shoulder stability by increasing the glenoid surface and providing attachments for the shoulder capsule and various ligaments and tendons. Overhead arm activities, especially throwing, can stress the shoulder excessively and cause labral injury. Symptoms include poorly localized pain, exacerbated by overhead and behind-the-back motions, and popping, catching, or grinding. Imaging includes AP, outlet, and axillary radiographs, but CT arthrogram or MR arthrogram is also recommended. Fractures and dislocations should be referred. In other labral injuries, 2 to 4 weeks of rest and physical therapy may resolve symptoms. If not, patients should be referred for further testing and possible surgery.
The shoulder has the greatest range of motion of any joint in the body, making it tremendously versatile. This versatility, however, comes at the price of the relative instability of the glenohumeral joint. Normal shoulder function and stability depend on the maintenance of a delicate balance between the static and dynamic constraints in the shoulder. Any injury that disturbs this balance can lead to pain, progressive weakness, biomechanical changes, instability, and progressive shoulder dysfunction.
Nowhere is optimum shoulder function more important than in athletes. In particular, athletes who engage in throwing and other overhead arm motions require a strong, stable shoulder to compete. The glenoid labrum plays an important role in maintaining shoulder function, and although labral injuries are relatively infrequent, they can sideline an overhead athlete. Familiarity with the throwing motion and shoulder anatomy can help primary care physicians diagnose, treat, and, when necessary, refer patients who have injuries to the glenoid labrum.
The Throwing Motion
Extensive study of throwing athletes has provided insight into the tremendous forces bearing on the shoulder. In the act of throwing (see figure 1 in the article, "Elbow Injuries in Young Baseball Players"), the arm is abducted about 100° throughout most of the motion. External shoulder rotation of 175°, including scapulothoracic motion and trunk extension, is common. In the follow-through phase, up to 105° of internal rotation has been measured. In addition, the speed of arm rotation has been calculated at an astonishing 7,000° per second. These factors impose tremendous torque on the shoulder, particularly during deceleration. If these forces are not modulated and controlled by the soft tissues of the shoulder, injury follows (1,2).
Electromyography studies have shown that during the acceleration phase, the pectoralis major, serratus anterior, latissimus dorsi, and subscapularis muscles are actively contracting while the rotator cuff and biceps are relatively silent. Conversely, during the deceleration phase, the rotator cuff and trunk muscles show the most activity (3).
Glenoid Labrum Anatomy and Shoulder Stability
The shoulder is intrinsically unstable. The bony anatomy—the articulation of the large humeral head with the small glenoid cavity—confers relatively little stability (figure 1) (4,5). Muscular activity around the scapula, which provides a stable site of origin for the rotator cuff muscles, normally positions the glenoid so that the proper glenohumeral relationship is maintained throughout the range of shoulder motion (6,7). Rowe and Zarins (8) have compared this relationship to a seal balancing a ball on its nose.
Shoulder stability is also enhanced by the glenoid labrum, a ring of fibrous tissue attached to the rim of the glenoid. It varies in size and shape and has a wedge-shaped appearance in cross section, very similar to that of the meniscus (9-11). The labrum serves to expand the size and depth of the glenoid cavity. It increases the superior-inferior diameter of the glenoid by 75% and the anterior-posterior diameter by 50% (5,12).
The form of the labrum's attachment to the edge of the glenoid varies. In some individuals, the attachment is meniscoid; the labrum has a free edge that extends over the rim of the glenoid onto the articular surface. An inexperienced arthroscopist can easily mistake this variant for a tear rather than a normal anatomic form. More often the labral attachment is continuous with the edge of the glenoid and blends directly into the articular surface (figure 2) (9-11).
Besides increasing the area and depth of the glenoid, the labrum serves as the primary attachment site for the shoulder capsule and glenohumeral ligaments. The primary function of these ligaments is to stabilize the shoulder, especially at the extremes of motion. Throughout the middle range of shoulder motion, shoulder stability is a product of the complex interaction of negative intra-articular pressure, muscle balance and cocontractions, joint congruity, and coordinated scapula activity (13,14).
The superior aspect of the glenoid labrum also serves as the attachment site for the tendon of the long head of the biceps muscle (figure 2). This site may be more vulnerable to injury and age-related degenerative changes than the rest of the labrum because of a relatively poor blood supply. Cooper et al (9) have shown that the labrum has a rich vascular supply to all but its superior aspect.
Recent studies by Pagnani et al (15) and Rodosky et al (16) confirmed that the biceps tendon plays an important role in maintaining anterior shoulder stability. They demonstrated that tension applied to the intact long-head tendon in cadavers significantly decreased the anterior, superior, and inferior translation of the humeral head. Conversely, when superior labrum anterior-to-posterior (SLAP) lesions (discussed on page 82) were created in cadaver models, destabilizing the biceps anchor, the result was a significant decrease in torsional stability and increased strain in the inferior glenohumeral ligament complex.
In addition, cadaver studies have demonstrated that SLAP lesions that destabilize the biceps tendon anchor significantly increase anterior-posterior and superior-inferior glenohumeral translation (15). In contrast, isolated anterosuperior labral tears without biceps involvement did not increase joint translation (17).
Thus, it appears that an intact labrum makes a critical contribution to shoulder stability by anchoring the long-head biceps tendon as well as the glenohumeral ligaments.
The most common mechanisms of injury to the glenoid labrum in athletes and the general public are acute and chronic excessive traction and compression. Forces resulting from excessive inferior traction (eg, carrying or dropping and catching a heavy object) and excessive superior traction (eg, lifting or stabilizing an object overhead) have both been described (W. Ben Kibler, MD, personal communication, 1994). Traction injuries are common in overhead athletes as a result of the chronic repetitive overload to the shoulder (17-19), placing pitchers, swimmers, and tennis players at higher risk for labral injuries than other athletes. Compression injuries also occur and may be caused by a fall on an outstretched arm with the shoulder forward flexed and externally rotated. Chronic overuse- and age-related attritional changes are also part of the spectrum of labral injuries (20,21).
It is essential to combine a careful history and complete physical exam of the shoulder to diagnose labral injuries on clinical grounds.
Labral injuries often occur in association with other shoulder pathology, making the diagnosis challenging. In patients who have a history of shoulder instability, either dislocation or subluxation, or a traction or compression injury to the shoulder, a labral injury should be considered (22).
Signs and symptoms. Most often, patients will complain of poorly localized pain in the shoulder, often exacerbated by overhead and behind-the-back arm motions. They may also describe mechanical symptoms such as popping, catching, or grinding.
Physical findings may be subtle and nonspecific, adding to the difficulty of diagnosis. The patient may describe pain in the shoulder with resisted biceps contraction. Tenderness directly over the anterosuperior glenohumeral joint is not uncommon.
Physical tests. Several authors have described clinical tests that have varying degrees of sensitivity and specificity in the diagnosis of labral injuries. Kibler (23) published the first report of a diagnostic clinical test, the anterior slide test (figure 3a), which had a sensitivity of 78% and specificity of 91.5%. Liu et al (24) and O'Brien et al (25) have also described similarly reliable clinical tests for labral injuries; the O'Brien test is shown in figure 3b. The compression-rotation, or crank, test (14) (figure 3c)—analogous to the McMurray test of the knee—is also useful. One test is not necessarily more reliable than the others, and the findings of all aid the clinical diagnosis.
Plain x-rays, including anteroposterior (AP), outlet, and axillary views, should be obtained for all patients who have shoulder pain. Although normal x-rays do not rule out labral injury, plain x-rays may reveal loose bodies. The AP view may show an avulsion fracture of the supraglenoid tubercle, a rare fracture (26). An axillary view can help confirm a properly reduced glenohumeral joint and help reveal any bony detachment from the glenoid, and an outlet view provides an excellent look at the subacromial arch in cases of impingement. A West Point view may expose Hill-Sachs lesions and may be helpful in cases of suspected dislocation.
Presently, the preferred imaging studies for labral injuries include computed tomography arthrogram and magnetic resonance (MR) arthrogram. Both have shown excellent sensitivity and specificity for labral injuries.
Referral or conservative treatment? Primary care physicians who treat shoulder problems must rule out a fracture or dislocation in the initial assessment. If either of these conditions cannot be excluded, referral to an orthopedist is appropriate.
For the patient who has a painful shoulder that is not fractured or dislocated, a short period of conservative treatment is indicated. This generally includes rest, mild analgesia, and physical therapy, consisting of gentle range-of-motion and strengthening exercises and modalities such as heat, ice, and electric stimulation for pain. If the patient does not improve significantly within 2 to 4 weeks, he or she should be referred to an orthopedic surgeon for further examination, diagnostic testing, and surgery, if indicated.
Surgery. Excluding labral injuries that involve fractures and dislocations, arthroscopy should be done only after a trial of conservative treatment. The specific surgical intervention is determined by the type of labral injury. The most widely accepted classification system for these injuries defines them as SLAP or non-SLAP lesions. Both can be further classified as stable or unstable.
SLAP. SLAP lesions are injuries to the labrum that extend from anterior to the biceps tendon to posterior to the biceps tendon. Snyder (18,20,21) divided these injuries into four types, as shown in figure 4.
SLAP lesions are either stable or unstable, depending on whether the majority of the superior labrum and the biceps tendon are firmly attached to the glenoid margin. Unstable lesions (types 2 and 4) can generally be repaired arthroscopically by reattaching the labrum to the glenoid. For stable lesions (types 1 and 3), arthroscopic debridement to eliminate mechanical irritation is usually adequate.
Non-SLAP. Stable non-SLAP injuries, including degenerative, flap, and vertical labral tears (20,21), can be treated with arthroscopic debridement. Unstable non-SLAP injuries, such as Perthes and Bankart lesions, should be treated with arthroscopic fixation.
Address Shoulder Stability
Shoulder stability must be addressed in patients who have labral lesions, which are often associated with capsular injury. In the absence of associated injuries and evidence of shoulder instability, treatment of the labral injury, as described above, is usually adequate. In patients who have an unstable shoulder, as demonstrated by episodes of subluxation or dislocations, the diagnostic challenge is to accurately define the pathologic lesion to permit treatment of the instability as well as the labral injury.
A detailed look at all of the patterns of shoulder instability and specific pathologic features is beyond the scope of this article. However, shoulder instability generally involves a spectrum of injury to the glenohumeral ligaments, from mild stretching or attenuation that causes mild instability with transient subluxation, to complete avulsion of the glenohumeral ligaments from the glenoid or the humerus with associated frank instability. The goal of surgery is to restore the anatomy to its normal state and provide adequate stability to allow proper healing and facilitate maximal rehabilitation.
The function of the glenoid labrum is just beginning to be understood. Although small and seemingly insignificant, it appears to play a vital role in maintaining shoulder stability and normal function. Though labral injuries are not common, they are clinically significant. Their nonspecific symptoms and the complexity of possible associated injuries present the sports medicine physician with diagnostic and treatment challenges.
Dr Richards practices orthopedic surgery and sports medicine in the Lexington Clinic Sports Medicine Center in Lexington, Kentucky. He is a team physician for several local high schools and colleges and is a fellow of the American College of Sports Medicine. Address correspondence to David B. Richards, MD, Lexington Clinic, 700 Bob-O-Link Dr, Lexington, KY 40504.