The shoulder is the most unstable joint in the animal kingdom. In 1986, Calvin proposed a theory for why humans developed this evolutionary liability. He postulated that the ability to throw objects was a major contribution to the evolution of Homo sapiens. Our ancestors used the act of throwing rocks while hunting animals. Calvin explains that during the rapid development of the human brain, it acquired a large number of neurons to cope with a large range of shoulder movement to achieve accurate throwing. It is this range of motion that makes the joint unstable.
Imaging plays an important role in the assessment of labral injuries and includes conventional radiography and computed tomography (CT) or magnetic resonance (MR) arthrography. [1, 2] Labral injuries associated with fractures and dislocations need urgent surgical attention.  Other labral injuries are initially treated in an expectant manner, with 2-4 weeks of rest and physiotherapy.
The following are some images of normal shoulder anatomy.
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 injuries. 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, which contributes to shoulder stability by increasing the glenoid surface.
Normally, a delicate balance exists between the 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 also cause labral injury. 
The subject of glenohumeral instability is complex. The 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 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.
In 1923, Bankart described the "essential lesion"—that is, a single abnormality that causes recurrent instability of the shoulder joint. Initially, he stated that the essential feature is the detachment of the capsule from the labrum. In 1938, he modified his thinking, suggesting that the labrum shears off from its bony attachment at the glenoid rim. He proposed that these lesions be treated by reattaching the labrum to the bone.
Rotator Cuff Tendons
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 the junction of the labrum and glenoid. The anterior proximal capsule may also 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. The average retroversion of the glenoid in habitual anterior dislocations is 0.3°, and it is 10-12° in posterior dislocations. On CT scans, the glenoid inclination angle can easily be measured through the midpoint of the glenoid. However, normal and abnormal angles significantly overlap, and therefore, the measurement is clinically useful only in extreme cases.
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 may sometimes go unrecognized, even by the patient.
The direction in which the humeral head is subluxed is also variable and may take any direction, or it may be multidirectional. Many bony, ligamentous, tendinous, and muscle elements contribute to joint stability, although the individual contribution of these structures has long been debated. However, 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 the various components of the glenohumeral joint have been recognized, and no longer are the depiction of a Bankart lesion and a Hill-Sachs lesion regarded as sufficient diagnostic criteria for glenohumeral instability. However, these 2 lesions remain important, as they allow for the documentation of a previous anterior glenohumeral dislocation. Hurley and Anderson found anteroinferior labral tears in 92% of shoulders with recurrent subluxation or dislocations. [5, 6]
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 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. See the following images.
Bankart described this lesion as an unusual condition affecting individuals with epilepsy and athletes, above all football players, reporting only 27 cases in 1923-1938. 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 existed, it must be rare.
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. See the images below.
Superior labral, anterior and posterior lesion
A superior labral, anterior and posterior (SLAP) lesion is often seen in athletes involved with sports with repetitive overhead arm activities. The lesion affects the superior portion of the glenoid labrum and occasionally the biceps anchor. 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 among 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. 
Singson et al performed double-contrast CT arthrography in 54 shoulders in 53 patients with recurrent dislocation or subluxation and observed no difference in the degree or number of labral lesions between subluxations and dislocations.  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 2 most common abnormalities. 
Rafii et al examined 60 professional and recreational athletes with CT arthrography of the shoulder and determined CT arthrography is a minimally invasive and highly accurate technique for evaluated suspected glenohumeral derangement.  The investigators noted that the extent of pathologic changes associated with instability can be determined and differentiated from other intraarticular causes of incapacity, such as labral tears caused by throwing, or degenerative changes. 
The Bennett lesion represents an enthesophyte arising from the posterior portion of the glenoid rim, which 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 posterior labrum. This lesion may represent an acute form of a Bennett lesion.
Yu et al used MR imaging (MRI) to examine 6 male athletes aged 19-43 years with POLPSA lesions and found that the size of the periosteal sleeve and redundant joint recess was variable.  Fibrous proliferation was noted arthroscopically beneath the sleeve in 4 shoulders. Although the posterior labrum was detached in all studies, only 1 labrum had a tear, whereas 2 showed marked degeneration. 
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 usually due to an incompetent anterior portion of the inferior glenohumeral ligament complex. See the image 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.
Glenolabral articular disruption
A glenolabral articular disruption (GLAD) occurs with a 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 (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 being increasingly recognized as a normal anatomic variant. This foramen is placed between the anterosuperior parts 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.
Controversy exists among orthopedic surgeons regarding the role of imaging in glenohumeral instability in all patients. 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.
Because most shoulder instabilities can be diagnosed on the basis of the patient's history, physical findings, and conventional radiographs, 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 in whom the clinical diagnosis is certain and who can be referred for arthroscopy without any form of imaging and (2) patients in 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, as he or she may alter the treatment (eg, arthroscopic vs open surgery) accordingly. The deficiencies of standard MRI in depicting lesions associated with glenohumeral instability have led to the increasing use of arthrographic techniques. See the images below.
Arthrography may be carried out in conjunction with CT scanning or MRI. Both of these techniques improve delineation of the capsular attachments, the labrum and glenohumeral ligaments, as compared with standard CT scanning or MRI. Because soft-tissue contrast is better with MRI than with CT scanning, 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 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 an assessment of the labrum, the process is complicated by the considerable variation in the size and morphology of the labrum in asymptomatic individuals. Variations in the signal intensity of the labrum and surrounding structures, such as the glenohumeral ligaments and the long biceps tendon, are also seen in asymptomatic individuals; these variations are further sources of false-positive diagnoses.
Most of the 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 in identifying 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 the 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%, was 92% specific, 42% sensitive, and had a negative predictive value of 83%.  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. 
A level 3, diagnostic study by Ricchetti et al showed that the sensitivity of preoperative MRI with combined lesions of the anterior, posterior, and superior labrum is low at 8.7% tears detected by noncontrast MRI, compared with 33.3% by MR arthrography compared with arthroscopy. 
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 the potential pitfalls. Familiarity with the limitations of techniques and normal anatomic variants is therefore important. Potential problems associated with arthrography include discomfort to 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 help reveal any bony detachment from the glenoid, and an outlet view provides an excellent view of the subacromial arch in cases of impingement. See the images below.
A West Point view depicts Hill-Sachs lesions and is also a useful view for suspected dislocation. The Hill-Sachs defect can occur after only 1 dislocation. It is 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, a compression fracture of the posterolateral surface of the humeral head due to impaction by the anteroinferior rim of the glenoid during dislocation (Bankart lesion). It is best seen on the AP projection with the arm internally rotated 70-90°. An axillary view depicts the origin of the defect.
A posterior dislocation accounts for less than 5% of glenohumeral dislocations. Unlike an anterior dislocation, the posterior dislocation is characterized by a humeral head at the same level as the glenoid, and the radiographic findings on AP images may be subtle.
The most common causes of posterior dislocations are convulsive seizures in which bilateral dislocations may occur. On AP radiographs, the shoulder appears fixed in internal rotation. The width of 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, and the other represents the margin of the troughlike impacted fracture. The diagnosis can be confirmed with an axillary or a 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 usually the result of a blow on 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. In this injury, the head of the humerus penetrates the thoracic wall when a great force is applied to the head of the humerus from the lateral aspect, such as 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. In posterior dislocation, findings on plain radiographs may be subtle, and the dislocation is easily missed.
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 of 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 well seen on CT. However, the site of the tendon of long head of the biceps may difficult to discern on standard CT, although visualization is expected to improve with multisection CT.
A study by Yeo et al determined that multidetector CT arthrography is highly accurate in diagnosing SLAP lesions. It was also found to have good interobserver reliability; however, it has limitations in classifying specific labral tears. 
Capsular morphology is well depicted on CT scanning. Many of the insertion sites are considered anatomic variants. However, many authors believe that insertion of the capsule along the neck of the scapula predisposes to shoulder instability.
Wilson et al found that 86% of their patients with capsular insertion at the base of the scapular neck had labral tears on CT arthrography, whereas the rate was 50% in patients in whom the capsular insertion was to the glenoid or capsular neck.  The 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. 
The articular surface of the glenoid and humeral head are both covered by hyaline cartilage. The 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 cartilage covering the humeral head is visualized in approximately 50% of individuals. CT arthrography may depict focal defects in the humeral hyaline cartilage, and diffuse or focal irregularity of the glenoid cartilage is associated with osteoarthrosis secondary to shoulder joint instability.
Classification of labral tears
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 is complete segmental absence of the labrum; and grade III, which is a fracture of the bony rim of the glenoid invariably associated with a labral tear. 
Contraindications to CT arthrography
Contraindications to CT arthrography are skin infection overlying the shoulder and hypersensitivity to local anesthetic or iodinated contrast media. A problem encountered in the young is a vasovagal reaction.
Magnetic Resonance Imaging
The same dedicated coils and imaging planes are used in both MR arthrography and conventional MRI 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 sequence against the high signal intensity of gadolinium-based contrast agent that outlines the intra-articular structures. [15, 16, 17]
Oh et al prospectively compared the accuracy of three-dimensional (3-D) inotropic indirect MR arthrography with conventional indirect MR arthrography for diagnosing labral and rotator cuff lesions in 36 patients who underwent shoulder arthroscopic surgery and found no statistically significant differences in the 2 methods but that 3-D MRA can provide the same findings in a shorter imaging time.  The conventional sequences had a sensitivity of 74% and a specificity of and 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 the 3-D isotropic sequences, sensitivities and specificities 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 tendontears. 
The MR arthrographic sequences used vary in different centers and are tailored to the clinical case. The sequences generally include a T1-weighted fat-suppressed sequence applied in the 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) is added 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 external rotation, and in this stressed position, the 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 the avulsion of the glenoid labrum described in the Bankart lesion, disruption of the scapular periosteum is seen. See the images below.
A number of Bankart variants have been described in which the scapular periosteum is intact and associated with 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. The normal anchorage provided by the periosteum is lost, resulting in joint laxity. (2) The detached Perthe lesion occurs when the IGHLC is detached and displaced anteriorly (see the second image below). (3) In 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.
In the 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 the ABER position, the 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. An associated fracture of the humerus can be seen (ie, BHAGL lesion).
Recognition of the SLAP lesion is important because of the 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. The recurrent traction on the biceps tendon results in a tear of the superior glenoid labrum anterior and posterior to the long head of biceps tendon insertion. The severity of this lesion is classified based on the extent of damage to the labrum and the long head of biceps tendon involvement. See the images below.
Four types of this injury are described. Type1 is degeneration and fraying of only the superior labrum. In isolation, this type has doubtful significance in terms of shoulder stability. Type 2 is an avulsion of the superior labrum and long head of biceps tendon from the glenoid. Type 3 is a tear of the superior labrum with an intact biceps tendon insertion. Type 4 is extension of the tear into the proximal long head of the biceps tendon. The extent of damage to the biceps tendon mechanism is important to demonstrate, as this might be managed surgically.
Other findings associated with instability are paralabral cysts. These are also associated with SLAP lesions. The position of the cysts is closely related to the site of the labral tear. Fluid can be extruded into potential space—for example, into the suprascapular notch, compressing the nerve that results in muscle weakness and instability in the long term.
In addition to the IGHLC, the other components of the joint capsule and rotator cuff mechanism can be injured and must not be overlooked, particularly in the elderly population, in 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 the associated damage to the anterior shoulder capsule are seen. The latter injury results in anterior instability.
Posterior instability is less common than anterior instability and usually 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.
Limited data are available related to MRI in the reconstructed glenohumeral joint. Rand et al evaluated changes in capsular mechanisms and the labroligamentous complex with MR arthrography and suggested that changes in ligaments might be secondary to surgery and that MR angiography may be helpful in the reevaluation of patients with suspected recurrent instability.  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 the estimated volume in the axillary recess did not change significantly.  Extension of contrast material into preexistent labral tears decreased or was not evident postoperatively. Changes in the appearance of the glenohumeral ligaments were found in 6 patients. Changes in capsular distances might be indicative of a decreased capsular laxity and could be a valuable criterion in the evaluation of the postoperative shoulder. 
Postoperative follow-up of labral tears demonstrated a decrease in the extension of contrast agent into or under a tear. Reactive capsular thickening or scar tissue formation could be reactive or preexistent. 
The use of ferromagnetic suture anchors may cause balloon artifact on MRIs. Nonferromagnetic, plastic, or bioabsorbable suture anchors may leave evidence of violation of the glenoid neck on MRIs, whereas transglenoid sutures may leave channels traversing the glenoid neck.
Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Systemic Fibrosis. The disease has occurred in patients with moderate to end-stage renal disease after being 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. For more information, see the FDA Public Health Advisory or Medscape.
Degree of confidence
Jee et al studied MR arthrograms in 80 patients to determine the reliability and accuracy of MR arthrography in the diagnosis of SLAP tears and concluded that MR arthrography of the shoulder is reliable and accurate for detection of SLAP tears.  Sensitivity, specificity, and accuracy were 92%, 84%, and 86%, respectively. Interobserver agreement for SLAP tears was substantial to moderate.
Familiarity with the normal anatomic variation of the labrum is important to avoid a false-positive diagnosis.
Isolated anterosuperior labral tears are usually 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 rather than a torn labrum.
Anatomic variations in the 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 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 also 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, and therefore, the clinical relevance of labral lesions has been questioned. Labral tears have been found in asymptomatic individuals, as shown on MRI and on cadaveric studies. Many of these tears are found in older individuals and hence regarded as age related and of degenerative etiology. The glenoid labrum is loosely attached to the articular cartilage.
DePalma demonstrated that with aging, the labrum gradually detaches from the glenoid articular cartilage.  This phenomenon begins around the age of 50 years and is most marked at the superior aspect of 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. 
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 is occasionally 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.
The high accuracy in the depiction of labral tears and associated fractures indicates that ultrasonography can provide useful preoperative information in 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, tendonitis of the long head of the biceps, biceps tears, calcific tendonitis, and medial dislocation of the long head of the biceps tendon.
Degree of confidence
Ultrasonography is highly accurate for detecting full-thickness rotator cuff tears, in characterizing their extent, and in 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 in cadaveric specimens with arthroscopy as reference and determined this imaging modality has a promising role in evaluating the glenoid labrum, particularly in excluding labral tears when the labra appear normal on ultrasonography.  . The investigators examined 80 labral quadrants in 20 cadaveric shoulders using 5- to 7-MHz linear and curvilinear transducers, with an 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%, the positive predictive value was 94%, the 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%, the positive predictive value was 67%, the negative predictive value was 99%, and accuracy was 98%. 
Schydlowsky et al evaluated the usefulness of ultrasonography in detecting labral lesions in 29 patients with anterior shoulder dislocation before arthroscopy and found 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.  The latter were not visualized during ultrasonography.
Hammar et al evaluated 22 patients with one-sided anterior shoulder instability by using 3 dynamic scanning approaches (2 frontal and 1 axillary) and found that although the use of multiple approaches helped to prevent misinterpretation, the approaches did not significantly differ in the depiction of the anterior structures of the shoulder.  The investigators evaluated the anterior labrum, the anterior ligamental-capsular complex, and humeral head and glenoid rim fractures. Arthroscopy or arthrotomy was subsequently performed as the standard.
Ultrasonography correctly depicted the presence or absence of fractures of the humeral head or glenoid rim.  All 22 patients had anterior labral tears, of whom 21 tears were correctly depicted with ultrasonography. The labral tear was seen as a hypoechoic zone larger than 2 mm or as labral movement. The anterior ligamental-capsular complex was correctly evaluated in 14 patients. 
Only limited experience in the use of ultrasonography in these lesions is available to date, and the incidence of false-positive and false-negative results is not known.
Scintigraphy has proven to be valuable in the diagnosis of soft-tissue injuries.
Angiography has no direct role in the diagnosis of labral injuries; however, it may be indicated in cases of vascular complications associated with shoulder dislocation.
Degree of Confidence
Angiography remains the criterion standard in the investigation of vascular pathology.