Glenoid Labrum Injury Imaging

The shoulder has the greatest range of motion of any joint in the body, making it tremendously versatile. This versatility makes the joint unstable and liable to injury. In the United States, the incidence of shoulder dislocation is 23 per 100,000 person-years, with the highest rates in adults in their 20s. ^[1]  

Anatomically, the articulation of the large humeral head with the small glenoid cavity confers relatively little joint stability. The glenoid labrum provides attachments for the shoulder capsule and various tendons and ligaments; this contributes to shoulder stability by increasing the glenoid surface.

Normally, a delicate balance exists between static and dynamic constraints in the shoulder. Any injury that disturbs this balance can lead to instability, progressive shoulder dysfunction, and pain. The labrum may be torn with shoulder dislocations. Activities involving overhead arm movements, especially throwing and bowling, can stress the shoulder excessively and can cause labral injury. ^[2]

The topic of glenohumeral instability is complex. Methods of classification are based on the degree and direction of instability, its chronology, and its pathogenesis. The glenoid labrum plays an important role in maintaining shoulder function, and although labral injuries are relatively infrequent, when they do occur, they can incapacitate athletes. Traumatic detachment of the glenoid labrum is seen in 85% of patients after a traumatic anterior dislocation. The inferior glenohumeral ligament that is attached to the inferior half of the anterior glenoid labrum is the most important ligament that stabilizes the shoulder. With traumatic dislocation, the humeral head is displaced.

An anterior shoulder dislocation is associated with a Bankart lesion in 87-100% of cases, Hill-Sachs lesion in 90%, bony Bankart lesion in 73%, rotator cuff injury in 13%, and SLAP (superior labral lesion anterior to posterior (SLAP) in 10%. A Perthes lesion, anterior labral periosteal sleeve avulsion (ALPSA), glenolabral articular disruption (GLAD), and humeral avulsion of glenohumeral ligament (HAGL) occur in a minority of cases. ^[3]

Imaging plays an important role in assessment of labral injuries and consists of conventional radiography and computed tomography (CT) or magnetic resonance (MR) arthrography. ^{[4, 5]} Labral injuries associated with fractures and dislocations need urgent surgical attention. ^[6] Other labral injuries are initially treated in an expectant manner, with 2-4 weeks of rest and physiotherapy.

MRI, because of its soft tissue contrast capability, is considered the first-line imaging modality for assessing joints. For patients who are claustrophobic or who have any contraindications to MRI, a computed tomography (CT) arthrogram is a suitable option. Arthrography remains a useful imaging modality, with CT and MRI allowing a detailed assessment of articular structures. ^[7]

When shoulder pathology is evaluated, it is crucial to obtain radiographs to assess osseous and joint structural abnormalities. Typically, MRI is performed after conventional radiographs have been evaluated. ^[7]

(See images of normal shoulder anatomy below.)

Rotator cuff tendons

The rotator cuff is a group of muscles and tendons that support the shoulder joint. Rotator cuff disease is a frequent cause of morbidity in adulthood. ^[8]  The rotator cuff tendons blend in with the capsule posteriorly, superiorly, and anteriorly. Distally, the capsule inserts into the anatomic neck of the humerus, and proximally, the capsule is attached to the scapula. The posterior proximal capsule attaches either to the labrum or to the junction of the labrum and the glenoid. The anterior proximal capsule may attach to the labrum or to the neck of the scapula or occasionally more medially to the base of the scapular neck.

The glenoid inclination refers to the relationship of the glenoid articular surface and the transverse axis of the scapula. Normally, slight retroversion of approximately 5° is present but with a range of up to 25° in retroversion and 8° in anteversion. Average retroversion of the glenoid in habitual anterior dislocations is 0.3°, and it is 10° to 12° in posterior dislocations. On CT, the glenoid inclination angle can be measured easily through the midpoint of the glenoid. However, normal and abnormal angles significantly overlap; therefore, this measurement is clinically useful only in extreme cases.

In a study by Eustace et al of 597 patients (mean age, 49.4 ± 17.1 yr) who underwent shoulder MRI because of atraumatic shoulder pain, subacromial bursitis was identified in 517 patients, supraspinatus full-thickness tear in 102, and degenerative acromioclavicular joint in 370. The authors noted that extent of rotator cuff and acromioclavicular joint degeneration increases with older age and that mpingement appears to trigger a sequential cascade of events, from isolated subacromial bursitis through to supraspinatus tendon tearing. ^[8]

Associated and other injuries

The spectrum of glenohumeral joint instability is wide, ranging from joint dislocation, which is easily recognizable on clinical examination, to transient glenohumeral joint subluxation, which may be difficult to recognize, as the joint may spontaneously relocate. This event sometimes goes unrecognized, even by the patient.

The direction in which the humeral head is subluxed is also variable and may take any direction, or subluxation may be multidirectional. Many bony, ligamentous, tendinous, and muscular elements contribute to joint stability, although the individual contributions of these structures have long been debated. Authorities generally agree on the important contribution of glenohumeral ligaments to joint stability despite inconsistencies in their size.

With the advent of shoulder joint arthroscopy, an increasing number of abnormalities of various components of the glenohumeral joint have been recognized, and depiction of a Bankart lesion and a Hill-Sachs lesion is no longer regarded as sufficient for diagnosis of glenohumeral instability. However, these 2 lesions remain important, as they allow documentation of a previous anterior glenohumeral dislocation. Hurley and Anderson found anteroinferior labral tears in 92% of shoulders with recurrent subluxation or dislocation. ^{[9, 10]}

Bankart lesion

A Bankart lesion represents an anterior and inferior labral detachment from the glenoid with a capsuloligamentous injury below the equator of the glenoid. Arthur Sydney Blundell described the Bankart lesion as a traumatic detachment of the glenoid labrum. This lesion is seen in more than 85% of all cases after a traumatic anterior dislocation. At the time of the original injury, the humeral head is forced against the joint capsule and the inferior glenohumeral ligament, which it stretches. Then, as a result of traction, the fibrous labrum is pulled off from the inferior half of the anterior rim of the glenoid. ^[3]

(See the following images.)

Bankart described this lesion as an unusual condition affecting individuals with epilepsy and athletes, most often football players, with only 27 cases reported from 1923 to 1938. How the term Bankart lesion became embedded in the radiology literature is unclear, as Bankart emphatically denied the presence of a glenoid rim fracture in any of his cases. He stated that he had never seen a recurrent dislocation associated with a glenoid fracture and went on to say that if such an association exists, it must be rare.

A bony Bankart lesion refers to a fracture of the anteroinferior glenoid rim. ^[11]

Hill-Sachs lesion

Harold Arthur Hill and Maurice D. Sachs were 20th century American radiologists who described the association between an anterior dislocation of the glenohumeral joint and a compression fracture of the posterolateral aspect of the humeral head. This type of injury is caused by impaction of the humerus against the anterior rim of the glenoid cavity. ^{[12, 13, 14, 15, 16]}

(See the images below.)

The most common method of assessing the Hill-Sachs lesion is the Calandra classification, which uses arthroscopy to measure the depth of the lesion as follows ^[17] :

• Grade I: Defect in articular surface that does not affect subchondral bone
• Grade II: Defect that includes subchondral bone
• Grade III: Large defect in the subchondral bone

In a study of the characteristics of Hill-Sachs lesions using 3D CT in patients with anterior shoulder instability, Golijanin et al identified a statistically significant association between medialization and volume, position, and orientation. More medialized lesions had a larger volume, greater width, more surface area loss, and higher lesion angles and were more inferior in the humeral head. More medialized lesions had poorer clinical outcomes. ^[12]

Three-dimensional CT is considered the gold standard for evaluation of  Hill-Sachs lesions. Measurement of depth and width of axial slices on CT scan has shown good reliability, but 3D CT has been reported to be more accurate than 2D. Lesions that are bigger and more horizontally oriented to the humeral shaft have been shown to have a greater probability of being engaging. The on-track off-track method has been shown to be an accurate predictor of engagement. The glenoid track refers to the area of contact between the humeral head and glenoid and is defined as approximately 83% of glenoid width. A Hill-Sachs defect that is smaller than the track (ie, on-track) will maintain contact and is at lower risk of engagement and instability, while a Hill-Sachs defect larger than the glenoid track (ie, off-track) will be at increased risk of engagement and instability (ie, engaging Hill-Sachs defect). ^{[13, 14, 15, 16]}

Superior labral anterior and posterior lesion

A superior labral anterior and posterior (SLAP) lesion is often seen in athletes who perform repetitive overhead arm activities. This lesion affects the superior portion of the glenoid labrum and occasionally the biceps anchor. ^{[18, 19]}

Both athletic and general populations can be affected by SLAP lesions. Based on cross-sectional imaging findings, SLAP tears can be divided into 4 main types (I-IV) and 6 extended types (V-X). An accurate description of imaging findings of the SLAP tear type, along with concomitant findings, can aid in treatment planning. ^[20]

(See the following images.)

Labral abnormalities with posterior shoulder joint instability

Labral abnormalities are frequently seen in association with anterior instability of the shoulder joint. By contrast, relatively few labral abnormalities are seen with posterior instability. Hurley et al found no posteroinferior labral tears in 3 shoulders with posterior instability and 4 patients with multidirectional instability. Patients with posterior shoulder instability had increased glenoid retroversion when compared with an uninjured population. ^[9]

Singson et al performed double-contrast CT arthrography in 54 shoulders of 53 patients with recurrent dislocation or subluxation and observed no difference in the degree or number of labral lesions between subluxations and dislocations. ^[21] However, more severe capsular lesions, subscapularis tendon tears, and widened subscapularis bursae were consistently found in patients with dislocations. Lesions of the anterior labrum in 52 (96%) of 54 cases and of the capsuloligamentous complex in 42 (78%) of 54 cases were the most common abnormalities. ^[21]

Rafii et al examined 60 professional and recreational athletes with CT arthrography of the shoulder and determined that CT arthrography is a minimally invasive and highly accurate technique for evaluating suspected glenohumeral derangement. The investigators noted that with CT arthrography, the extent of pathologic changes associated with instability can be determined and differentiated from other intra-articular causes of incapacity (eg, labral tears caused by throwing; degenerative changes). ^[22]

Bennett lesion

The Bennett lesion represents an enthesophyte arising from the posterior portion of the glenoid rim; it is commonly seen in baseball pitchers. The posterior labrocapsular periosteal sleeve avulsion (POLPSA) lesion is an abnormality that can be associated with posterior instability. It differs from a reverse Bankart lesion in that the periosteum, although detached, remains intact with the posterior capsule and detached from the posterior labrum. This lesion may represent an acute form of a Bennett lesion. ^[23]

In a study by Knapik et al of 5,662 scapulae from 2,831 individual cadaveric specimens from individuals older than 18 years at the time of death, Bennett lesions were identified in 3.5% of osseous specimens and 1.8% of scapulae, with a higher prevalence in specimens from males and African Americans. ^[23]

POLPSA lesion

Yu et al used MRI to examine 6 male athletes aged 19 to 43 years with POLPSA lesions and found that the size of the periosteal sleeve and redundant joint recess was variable. ^[24] Fibrous proliferation was noted arthroscopically beneath the sleeve in 4 shoulders. Although the posterior labrum was detached in all cases, only 1 labrum had a tear, whereas 2 showed marked degeneration. ^[24]

Perilabral ganglion cyst

A perilabral ganglion cyst is often associated with a labral tear.

Anterior labroligamentous periosteal sleeve avulsion

The anterior labroligamentous periosteal sleeve avulsion (ALPSA) lesion is seen in association with recurrent anterior glenohumeral dislocation and is usually due to an incompetent anterior portion of the inferior glenohumeral ligament complex.

(See the images below.)

Humeral avulsion of the glenohumeral ligament

The humeral avulsion of the glenohumeral ligament (HAGL) lesion is also associated with recurrent anterior glenohumeral instability, but it is generally seen in older individuals. A HAGL lesion becomes a bony HAGL (BHAGL) lesion when, in addition, a bone fragment is avulsed from the humeral insertion of the inferior glenohumeral complex. ^[25]

HAGL lesions are most commonly seen in patients who have an anterior instability without a Bankart tear or in patients who have continued symptoms despite a Bankart repair. The most common type of humeral avulsion of the glenohumeral ligament is a ligamentous avulsion that involves the anterior inferior glenohumeral ligament. ^[25]

Glenolabral articular disruption

A glenolabral articular disruption (GLAD) occurs with a superficial tear of the anteroinferior portion of the labrum and avulsion of articular cartilage of the glenoid fossa and has no association with glenohumeral joint instability. Patients ordinarily have pain rather than frank instability symptoms. ^[26]

(See the images below.)

Arthroscopy has depicted many normal variants within the glenohumeral joint, leading to the introduction of many terms and acronyms. A sublabral foramen is increasingly recognized as a normal anatomic variant. This foramen is placed between anterosuperior portions of the glenoid labrum and the articular cartilage of the glenoid cavity. In up to 18% of patients, normal clefts (eg, sublabral holes) can be seen, and in less than 6%, other rare variations (eg, Buford complex) are seen. A Buford complex is a cordlike middle glenohumeral ligament associated with absence of the anterosuperior portion of the glenoid labrum.

Imaging modalities

The American College of Radiology (ACR) has provided criteria for selecting the imaging modalities of choice for patients with traumatic or atraumatic shoulder pain. Imaging examination choices are based on the etiology of shoulder pain (whether traumatic or atraumatic), the duration of symptoms, patient age at presentation, and any clinical or radiographic suspicion for a particular condition. The ACR recommends that the initial imaging modality for traumatic or atraumatic shoulder pain be radiography. The next imaging choice should be guided by the clinical scenario and by findings from plain films. ^[7]

Controversy exists among orthopedic surgeons regarding the role of imaging in glenohumeral instability. Some argue that arthroscopy improves the diagnostic yield and also serves as a therapeutic tool. However, arthroscopy is invasive, and many orthopedic surgeons concede that an accurate diagnosis of virtually any symptomatic problem involving the shoulder joint is needed before therapeutic intervention is undertaken.

Understanding shoulder anatomy, injury patterns, and surgical procedures is essential for image interpretation. Although the rotator cuff cannot be directly evaluated, radiographs of the shoulder provide the initial evaluation of osseous abnormalities associated with rotator cuff impingement. MRI is considered the study of choice for evaluation of the shoulder because it provides comprehensive assessment of both bone and soft tissue abnormalities. MRI can accurately reveal the size and shape of tendon tears, tendon tear retraction, and tendon and muscle quality. CT is an excellent modality for evaluation of osseous detail and for detection of gas and calcium deposition; however, conventional CT is much less sensitive for detection of bone marrow edema and soft tissue detail of the rotator cuff. Ultrasound can assess the rotator cuff with results similar to those of MRI, but ultrasound cannot evaluate osseous structures. ^[27]

Imaging of the postoperative shoulder joint reveals complex, diagnostically challenging changes regarding anatomic structures. The broad spectrum of complex findings and continually developing and changing surgical procedures present significant challenges for radiologic evaluation of the postoperative shoulder joint. To differentiate physiologic reactions from pathologic changes, it is necessary to have general knowledge of common surgical procedures, expected postoperative findings, and possible complications. Use of a variety of imaging modalities can further advance diagnostic precision. ^[28]

Because most shoulder instabilities can be diagnosed on the basis of patient history, physical findings, and conventional radiography, the use of MRI solely to diagnose instability appears unwarranted. Although glenohumeral instability and rotator cuff disorders were once thought to be mutually exclusive, this is no longer considered to be true. Many authors have shown that patients who have disease of the rotator cuff or symptoms of impingement have associated shoulder joint instability. MRI is the imaging study of choice for assessing rotator cuff problems.

Two categories of patients have been described: (1) patients for whom the clinical diagnosis is certain and who can be referred for arthroscopy without any form of imaging and (2) patients for whom the clinical diagnosis is uncertain and who should be referred for imaging of the shoulder joint.

Radiographic studies may be undertaken first and should include special views to delineate specific lesions such as the Bankart lesion and the Hill-Sachs defect. MRI offers several advantages, including its ability to depict other abnormalities that may mimic shoulder instability on clinical examination. This information is of importance to the orthopedic surgeon, because it may alter treatment (eg, arthroscopic vs open surgery) accordingly. Deficiencies of standard MRI in depicting lesions associated with glenohumeral instability have led to increasing use of arthrographic techniques.

(See the images below.)

Arthrography may be carried out in conjunction with CT or MRI. Both of these techniques improve delineation of capsular attachments—the labrum and glenohumeral ligaments—as compared to standard CT or MRI.

Historically, arthrography was performed with fluoroscopy and plain radiography only, but now patients regularly undergo cross-sectional imaging of the shoulder after injection of contrast. This is typically done with MRI, but it can also be performed with CT if there are contraindications to MRI or if there is high clinical suspicion of a bony abnormality. ^[7]

Because soft tissue contrast is better with MRI than with CT, MRI is the preferred arthrographic technique.

(See the following MR arthrograms.)

Two techniques are used in MR arthrography: (1) the direct method, in which a gadolinium-based contrast agent, an iodinated contrast agent, or saline is injected into the joint space, and (2) the indirect method, in which an intravenous injection of a gadolinium-based contrast agent is given and in which delayed images are obtained at 20 minutes with or without shoulder exercise. Direct MR arthrography improves definition, but it is invasive and labor intensive for the radiologist, although it is safe.

Limitations of techniques

MRI is expensive and has limitations associated with metallic implants, certain cardiac pacemakers, ferromagnetic foreign bodies, and claustrophobia. Although standard MRI and CT and MR arthrography allow for assessment of the labrum, this process is complicated by considerable variation in size and morphology of the labrum in asymptomatic individuals. Variations in signal intensity of the labrum and surrounding structures such as glenohumeral ligaments and the long biceps tendon are also seen in asymptomatic individuals; these variations serve as additional sources of false-positive diagnosis.

Most anatomic variants and lesions can be depicted at arthroscopy, but whether MRI can depict all of these is unclear. The presence of fluid in the glenohumeral joint helps identify these variants and pathologic lesions. Therefore, standard MRI performed in patients with a history of glenohumeral instability with no associated joint effusion is not a reliable test for these variations and pathologies.

Stetson and Templin compared results of the crank test, the O'Brien test, and routine MRI in the diagnosis of labral tears and found that MRI had a positive predictive value of 63%, specificity of 92%, sensitivity of 42%, and negative predictive value of 83%. ^[29] However, the O'Brien and crank tests did not provide sensitive clinical indicators for detecting glenoid labral tears and other tears of the anterior and posterior labrum. Results were often falsely positive for patients with other shoulder conditions, including impingement and rotator cuff tears. ^[29]

Special concerns

Imaging techniques have both false-positive and false-negative rates; moreover, there are normal variants that can be confused with pathology. The radiologist needs to be aware of potential pitfalls. Familiarity with the limitations of techniques and with normal anatomic variants is therefore important. Potential problems associated with arthrography include discomfort for patients, risk of septic arthritis, and the need for contrast administration.

Conventional radiographs, including anteroposterior (AP), outlet, and axillary views, should be obtained in all patients with suspected shoulder instability. Although normal radiographs do not rule out labral injury, conventional radiographs may reveal fractures, dislocations, loose bodies, and Bankart or Hill-Sachs lesions. The AP view may show an avulsion fracture of the supraglenoid tubercle—a rare fracture. An axillary view can help confirm a properly reduced glenohumeral joint and may reveal any bony detachment from the glenoid. An outlet view allows excellent assessment of the subacromial arch in cases of impingement.

(See the images below.)

A West Point view depicts Hill-Sachs lesions and is useful for suspected dislocation. The Hill-Sachs defect can occur after a single dislocation; this is seen as a tear of the anterior capsular complex, including the inferior glenohumeral ligament. Because the defect is posterolateral, it is best seen on a view with the humerus in internal rotation.

(See the image below.)

Dislocations of the glenohumeral joint are classified as anterior, posterior, inferior, or superior. More than 95% of all glenohumeral dislocations are anterior, in which the head of the humerus is displaced anterior to the glenoid (see the following image). Associated fracture of the anterior glenoid rim is best seen on the axillary view.

A large, fractured fragment is generally regarded as an indication for open surgery. More than 50% of anterior shoulder dislocations are associated with a Hill-Sachs defect—that is, a compression fracture of the posterolateral surface of the humeral head caused by impaction by the anteroinferior rim of the glenoid during dislocation (Bankart lesion). Hill-Sachs lesions are oriented in the axial plane at approximately 07:58 ± 00:48, or at an angle of 239.1 ± 24.3° from 12 o’clock. ^[30] . An axillary view depicts the origin of the defect.

Posterior dislocation accounts for less than 5% of glenohumeral dislocations. Unlike anterior dislocation, posterior dislocation is characterized by a humeral head at the same level as the glenoid; radiographic findings on AP images may be subtle.

The most common cause of posterior dislocation is convulsive seizures in which bilateral dislocations may occur. On AP radiographs, the shoulder appears fixed in internal rotation. The glenohumeral joint appears wider (>6 mm) because the humeral head is displaced laterally by the posterior glenoid rim. However, the associated impacted fracture of the humeral head may be displaced medially, leading to overlap of the glenoid rim and the humeral head. This impacted fracture is analogous to a Hill-Sachs lesion of an anterior dislocation and resembles 2 parallel lines of cortical bone on the superomedial aspect of the humeral head. One line represents the articular cortex of the head; the other represents the margin of the troughlike impacted fracture. Diagnosis can be confirmed with an axillary or scapular Y view.

(See the following image).

Inferior, superior, and intrathoracic dislocations are rare forms of trauma. Inferior dislocations occur with severe hyperabduction of the arm, causing impingement of the humeral head against the acromion process, which levers the humeral head out of its socket and displaces the head inferiorly. Superior dislocation is rare and is usually the result of a blow to the flexed elbow with the arm abducted, forcing the humeral head superiorly through the rotator cuff muscles and/or tendons to assume a position anterior to the acromion process. Intrathoracic dislocation is exceptionally rare. With this injury, the head of the humerus penetrates the thoracic wall when great force is applied to the head of the humerus from the lateral aspect, as may occur in a motor vehicle accident.

Axillary views should not be used to confirm adequate reduction because abduction of the arm predisposes the patient to recurrent dislocation. With posterior dislocation, findings on plain radiographs may be subtle, and dislocation is easily missed.

Computed tomography (CT) arthrography provides an excellent means to evaluate shoulder joint instability, as adequate visualization of the glenoid labrum is accomplished with this technique (see the image below). Abnormalities depicted on CT arthrography include labral attenuation and hypertrophy. Lesions of the long head of the biceps tendon have been reported in association with shoulder pain with or without clinical features of glenohumeral instability. Tendon insertion abnormalities may be seen, although not consistently. The shoulder joint capsule and its insertion sites are seen well on CT. The site of the tendon of the long head of the biceps may be difficult to discern on standard CT, although visualization is expected to improve with multisection CT.

Yeo et al determined that multidetector CT arthrography is highly accurate in diagnosing SLAP (superior labral anterior and posterior) lesions. Investigators found good interobserver reliability but limitations in classifying specific labral tears. ^[31]

Capsular morphology is well depicted on CT scanning. Many insertion sites are considered anatomic variants. However, researchers believe that insertion of the capsule along the neck of the scapula predisposes to shoulder instability.

Wilson et al found that 86% of patients with capsular insertion at the base of the scapular neck had labral tears on CT arthrography, whereas the rate was 50% among patients for whom capsular insertion was to the glenoid or the capsular neck. ^[32] Investigators also found that the overall size of the capsule had no correlation with labrum abnormalities. Rafii et al believe that capsular insertion along the neck of the scapula represents capsular stripping secondary to trauma and that associated periostitis is apparent on CT arthrography. ^[22]

Using 3D CT to evaluate Hill-Sachs lesions, Golijanin et al identified a statistically significant association between medialization and volume, position, and orientation. More medialized lesions had a larger volume, greater width, more surface area loss, and higher lesion angles and were more inferior in the humeral head. More medialized lesions had poorer clinical outcomes. ^[12]

The articular surface of the glenoid and the humeral head are covered by hyaline cartilage. Hyaline cartilage covering the glenoid is thinner at the center than at the periphery; the reverse is true for the humeral head.

CT arthrography depicts the articular cartilage covering the glenoid in all patients but reveals cartilage covering the humeral head in approximately 50% of individuals. CT arthrography may depict focal defects in the humeral hyaline cartilage; diffuse or focal irregularity of the glenoid cartilage is associated with osteoarthrosis secondary to shoulder joint instability.

El-Khoury et al classified labral tears as follows: grade I, which represents simple labral tears that appear as air contrast in the substance of the labrum or at the junction of the labrum and the glenoid articular cartilage; grade II, which shows complete segmental absence of the labrum; and grade III, which reveals fracture of the bony rim of the glenoid invariably associated with a labral tear. ^[33]

Contraindications to CT arthrography are skin infection overlying the shoulder and hypersensitivity to local anesthetic or iodinated contrast media. A vasovagal reaction may occur in young patients.

The same dedicated coils and imaging planes are used in magnetic resonance (MR) arthrography and in conventional MR shoulder imaging. Fat-suppressed sequences are now widely used in arthrography, as they improve contrast between the low signal intensity of bone marrow on fat-suppressed T1-weighted sequences versus the high signal intensity of gadolinium-based contrast agent that outlines intra-articular structures. ^{[34, 35, 36]}

Arthrography involves percutaneous puncturing into the shoulder joint and then instilling a contrast agent. Iodinated contrast is used for conventional arthrography and CT arthrography, whereas gadolinium contrast is used for MR arthrography. With conventional arthrography, radiographs are obtained after iodinated contrast is injected. With injection, distention of the shoulder capsule can be used therapeutically. MR arthrography is the gold standard for evaluating a suspected labral tear or shoulder instability. ^[7]

Oh et al prospectively compared the accuracy of 3-dimensional (3D) inotropic indirect MR arthrography (MRA) versus conventional indirect MRA for diagnosing labral and rotator cuff lesions in 36 patients who underwent shoulder arthroscopic surgery. Investigators found no statistically significant differences between the 2 methods but noted that 3D MRA can yield the same findings in a shorter imaging time. ^[37] Conventional sequences had a sensitivity of 74% and a specificity of 54% for superior labral lesions; 88% and 96%, respectively, for anterior labral lesions; 67% and 85%, respectively, for subscapularis tendon tears; and 96% and 75%, respectively, for supraspinatus-infraspinatus tendon tears. For 3D isotropic sequences, sensitivity and specificity were 70% and 85%, respectively, for superior labral lesions; 100% and 100%, respectively, for anterior labral lesions; 67% and 85%, respectively, for subscapularis tendon tears; and 96% and 67%, respectively, for supraspinatus-infraspinatus tendon tears. ^[37]

The MR arthrographic sequences used vary among centers and are tailored to the individual clinical case. Sequences generally include a T1-weighted fat-suppressed sequence, which is applied in coronal, axial, and sagittal planes with the patient's arm in neutral position. A T2-weighted fat-suppressed sequence is applied in the coronal plane with the arm in neutral position. In addition, an axial T1-weighted fat-suppressed sequence with the arm in abduction and external rotation (ABER) may be used to improve delineation of the inferior glenohumeral labroligamentous complex (IGHLC), the anteroinferior aspect of the glenoid labrum, and the undersurface of the rotator cuff tendon. The normal IGHL is taut in abduction and in external rotation; in this stressed position, IGHLC avulsions are accentuated.

(See the following images.)

In anterior instability, the vital structure that limits subluxation and dislocation in this direction is the IGHLC, and labral tears are most commonly seen at the anteroinferior aspect of the glenoid labrum. In the young patient, a constellation of findings that includes anteroinferior labral tears, damage to the inferior glenohumeral ligament, and the Bankart lesion is well recognized. This presentation is commonly seen after recurrent anterior dislocation. In conjunction with avulsion of the glenoid labrum as described in the Bankart lesion, disruption of the scapular periosteum is seen.

(See the images below.)

Several Bankart variants have been described in which the scapular periosteum is intact but there is anterior instability. These are summarized as follows: (1) The Perthe lesion is a nondisplaced avulsion of the labroligamentous complex with an intact scapular periosteum (see the first image below). The periosteum is medially stripped, creating a potential space. Anchorage normally provided by the periosteum is lost, resulting in joint laxity. (2) The detached Perthe lesion occurs when the IGHLC is detached and is displaced anteriorly (see the second image below). (3) With the ALPSA lesion, the torn anteroinferior labrum is displaced inferomedially by the inferior glenohumeral ligament that has rolled up the periosteum in a sleevelike manner (see the third image below). The displaced labroligamentous complex is attached to the glenoid by the intact anterior scapular periosteum. Overlying healing by fibrosis is observed.

With Perthe and ALPSA lesions in particular, the appearance of the glenoid labrum can be deceptively normal on conventional MRI and arthroscopy. On MR arthrography performed with joint distention and in the abduction and external rotation (ABER) position, detection of these injuries can guide the orthopedic surgeon to probe areas that appear normal on the surface. Tears to the inferior glenohumeral ligament, particularly the anterior band, result in anterior instability. Avulsion at or near the humeral attachment of the inferior glenohumeral ligament causes medial retraction of the ligament, which appears frayed and thickened; this is known as the HAGL lesion. Associated fracture of the humerus can be seen (ie, BHAGL lesion).

Recognition of the SLAP (superior labral tear anterior to posterior) lesion is important because of potential associated damage to the biceps tendon anchor, which has a role in anterior stability. This injury is recognized in athletes who perform recurrent throwing actions. Recurrent traction on the biceps tendon results in a tear of the superior glenoid labrum anterior and posterior to the long head of the biceps tendon insertion. Severity of this lesion is classified on the basis of extent of damage to the labrum and level of involvement of the long head of the biceps tendon. 

SLAP lesions are classified as follows ^{[38, 39]} :

• Type I: Degeneration and fraying of only the superior labrum 
• Type II: Avulsion of superior labrum and long head of biceps tendon from the glenoid
• Type III: Bucket-handle tear of superior labrum with intact biceps tendon insertion 
• Type IV: Type III lesion extending into the proximal long head of the biceps tendon
• Type V: Bankart-type labral disruption, which extends superiorly in continuity with a type II lesion
• Type VI: An unstable flap tear of the labrum in conjunction with a type II lesion
• Type VII: Superior labrum and biceps tendon separation that extends anteriorly through the capsule, inferior to the middle glenohumeral ligament
• Type VIII: Type II tear also involving cartilage adjacent to the biceps footplate

In addition, an Andrew lesion may be found in throwers. It consists of a pure superior labrum detachment without extension posterior to the biceps footplate and should not be confused with SLAP type II. ^[39]

(See the images below.)

Other findings associated with instability are paralabral cysts. These are also associated with SLAP lesions. Cysts are positioned close to the site of the labral tear. Fluid can be extruded into potential space—for example, into the suprascapular notch—compressing the nerve and resulting in muscle weakness and instability over the long term.

In addition to the IGHLC, other components of the joint capsule and the rotator cuff mechanism can be injured; this must not be overlooked, particularly in the elderly population, for whom the pattern of injury and presentation is different after a traumatic dislocation. A tear of the supraspinatus and an avulsion of the subscapularis tendon with associated damage to the anterior shoulder capsule may be seen. The latter injury results in anterior instability.

Posterior instability is less common than anterior instability and usually is the result of a sudden combined excessive force of internal rotation and adduction caused by posterior dislocation. The vector of forces results in posterior glenoid labrum and capsular injuries.

Postoperative findings

Limited data are available related to MRI in the reconstructed glenohumeral joint. ^[40] Rand et al evaluated changes in capsular mechanisms and in the labroligamentous complex with MR arthrography; they suggested that changes in ligaments might be secondary to surgery and that MR angiography may be helpful in reevaluating patients with suspected recurrent instability. ^[41] The investigators compared capsule thickness, capsular leaking, estimated volume of the axillary recess, appearance of the glenohumeral ligaments, and evidence of labral lesions on preoperative and postoperative images.

Preoperative capsular leaking was suspected in 7 patients, but it was not evident postoperatively. Capsular thickness and estimated volume in the axillary recess did not change significantly. ^[41] Extension of contrast material into preexistent labral tears had decreased or was not evident postoperatively. Changes in the appearance of glenohumeral ligaments were noted in 6 patients. Changes in capsular distance might be indicative of decreased capsular laxity and could serve as a valuable criterion in evaluation of the postoperative shoulder. ^[41]

Postoperative follow-up of labral tears revealed a decrease in extension of contrast agent into or under a tear. Reactive capsular thickening or scar tissue formation could be reactive or preexistent. ^[41]

In a study of 100 patients by Magee et al, MR arthrography was found to be more accurate than conventional MR in assessing postoperative shoulder pathology. CT arthrography detected additional pathology in cases of metallic artifact. The authors found it to be beneficial to inject a combination of gadolinium and CT contrast at arthrography, so that CT can be performed after arthrography if a metallic artifact prevents MR imaging of shoulder pathology. ^[40]

The use of ferromagnetic suture anchors may cause balloon artifact on MRI. Nonferromagnetic, plastic, or bioabsorbable suture anchors may leave evidence of violation of the glenoid neck on MRI, whereas transglenoid sutures may leave channels traversing the glenoid neck.

Degree of confidence

Studies investigating MRI and MRA in diagnosing SLAP tears have reported sensitivity and specificity ranging from 66% to 98% and from 13% to 89%, respectively. Variation in study design, differences in MRI methods used, and lack of reliability among observers likely account for such a wide discrepancy. ^[38]

Familiarity with normal anatomic variation of the labrum is important to avoid a false-positive diagnosis.

Isolated anterosuperior labral tears usually are not seen in patients with recurrent dislocation of the humeral head. A loose capsular attachment to the glenoid or a defect in the anterosuperior labrum is more likely to represent a normal anatomic variant than a torn labrum.

Anatomic variations in attachment of the glenohumeral ligaments can be another source of error, as they may mimic labral tears. A notch is occasionally seen anteroinferior to the site of attachment of the inferior glenohumeral ligament to the labrum. The confluence of the inferior glenohumeral ligament and the inferior labrum may occasionally obliterate the inferior labrum, which may account for poor accuracy of inferior labral tears. Many anatomic variations of the glenoid labrum have been described; these may mimic pathology. Attenuation and notching may be seen in asymptomatic individuals and are presumed anatomic variants.

Morphologic abnormality of the anterior labrum should be interpreted with caution, particularly in young athletes. Normal undercutting of the glenoid articular cartilage may mimic a torn labrum. When one is dealing with a detached labrum, it is important to pay particular attention to the high signal intensity separating the detached labrum from the glenoid margin. In labral tears, this hyperintense area is usually wider than the articular cartilage and extends over the glenoid margin beneath the capsular aspect of the labrum. A labral tear also has irregular margins.

Above the glenoid notch, a fluid-distended subscapularis bursa may be mistaken for capsular stripping. A type II or type III capsular insertion may also mimic capsular stripping. The diagnosis of capsular stripping is aided by the presence of an associated labral tear. The inferior glenohumeral ligament in association with a medial attachment of the capsule can sometimes be thrown into a ridge, which may be mistaken for labral tear. However, labral tears are seldom seen in this location.

Age-related changes are frequently found in the glenoid labrum; therefore, the clinical relevance of labral lesions has been questioned. Labral tears have been found in asymptomatic individuals, as shown on MRI and in cadaveric studies. Many of these tears are found in older individuals and hence may be regarded as age related and of degenerative etiology. The glenoid labrum is loosely attached to the articular cartilage.

DePalma found that with aging, the labrum gradually detaches from the glenoid articular cartilage. ^[42] This phenomenon begins around the age of 50 years and is most marked at the superior aspect of the glenoid at the site of biceps tendon attachment. With advancing age, fissuring, attenuation, and (at times) enlargement of the labrum due to synovial hypertrophy are also present. Degenerative changes within the labrum are depicted on MRI as an increase in signal intensity throughout the labrum or lack of definition of margins due to fraying. ^[42]

When a tear, degeneration, detachment, attenuation, or absence of the labrum is encountered, the location and age of the patient should always be taken into account before the glenohumeral instability is associated with the labral lesion. The normal anatomic humeral groove occasionally is confused with a Hill-Sachs lesion. A Hill-Sachs lesion is best differentiated from the anatomic groove by means of its more cephalic position along the longitudinal humeral axis.

Unless a shoulder joint effusion or injected contrast agent is present within the joint, the capsular insertion may be difficult to evaluate on MRI.

Ganglion cysts around the glenohumeral joint are frequently found; these cysts are significantly correlated with glenohumeral instability.

Following anterior shoulder instability surgery, patients may present with new or recurrent symptoms. Postoperative imaging, including MRI, may be obtained to assess the integrity of repaired tissues and of orthopedic fixation hardware or grafts. Familiarity with different operative techniques and their expected normal appearances and complications facilitates appropriate interpretation of these imaging studies. ^[43]

Gadolinium warning

Gadolinium-based contrast agents have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). This disease has occurred in patients with moderate to end-stage renal disease after they were given a gadolinium-based contrast agent to enhance MRI or MRA scans. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness.

High accuracy in the depiction of labral tears and associated fractures indicates that ultrasonography can provide useful preoperative information for patients with anterior shoulder instability. This modality is also useful in depicting other pathologies in patients presenting with shoulder pain, such as full-thickness tears of the supraspinatus tendon, tendinitis of the long head of the biceps, biceps tears, calcific tendinitis, and medial dislocation of the long head of the biceps tendon. ^[11]

Ultrasonography is highly accurate for detecting full-thickness rotator cuff tears, characterizing their extent, and visualizing dislocations of the biceps tendon. It is less sensitive in detecting partial-thickness rotator cuff tears and ruptures of the biceps tendon.

Taljanovic et al assessed the usefulness of ultrasonography in evaluating the glenoid labrum of cadaveric specimens with arthroscopy as reference and concluded that this imaging modality offers promise in evaluating the glenoid labrum, particularly for excluding labral tears when labra appear normal on ultrasonography. ^[44] . The investigators examined 80 labral quadrants in 20 cadaveric shoulders using 5- to 7-MHz linear and curvilinear transducers, with 86% concordance between ultrasonography and arthroscopy. In differentiating the abnormal labrum (tear or degeneration) from the normal labrum with ultrasonography, sensitivity was 63%, specificity was 98%, positive predictive value was 94%, negative predictive value was 86%, and accuracy was 88%. In differentiating labral tears from other labral conditions (degeneration or normality), sensitivity was 67%, specificity was 99%, positive predictive value was 67%, negative predictive value was 99%, and accuracy was 98%. ^[44]

Schydlowsky et al evaluated the usefulness of ultrasonography in detecting labral lesions in 29 patients with anterior shoulder dislocation before arthroscopy and found that ultrasonography had a sensitivity of 88% and a specificity of 67%. The investigators diagnosed arthroscopically detected labral lesions in 26 patients. All lesions affected the anterior labrum, whereas 6 extended to the posterior labrum. ^[45] The latter were not visualized during ultrasonography.

Hammar et al evaluated 22 patients with 1-sided anterior shoulder instability by using 3 dynamic scanning approaches (2 frontal and 1 axillary) and found that although use of multiple approaches helped prevent misinterpretation, these approaches did not significantly differ in depiction of anterior structures of the shoulder. ^[46] The researchers evaluated anterior labrum, anterior ligamental-capsular complex, and humeral head and glenoid rim fractures. They subsequently performed arthroscopy or arthrotomy as the standard.

In the study by Hammar et al, ultrasonography correctly revealed the presence or absence of fractures of the humeral head or the glenoid rim. All 22 patients had anterior labral tears, and the tears in 21 patients were clearly depicted on ultrasonography. The labral tear was seen as a hypoechoic zone larger than 2 mm or as a labral movement. The anterior ligamental-capsular complex was accurately evaluated in 14 patients. ^[46]