eMedicine Specialties > Radiology > Musculoskeletal

Shoulder, Dislocations: Imaging

Author: Gavin Yeh Tseng, MBBS, FRCR, FAMS, Consultant Radiologist, Department of Diagnostic Radiology, Raffles Hospital
Coauthor(s): Wilfred CG Peh, MD, MBBS, FRCP(Glasg), FRCP(Edin), FRCR, Clinical Professor, Faculty of Medicine, National University of Singapore; Senior Consultant Radiologist, Alexandra Hospital, Singapore
Contributor Information and Disclosures

Updated: Jul 31, 2009

Radiography

Findings

Anterior shoulder dislocation and instability

Radiographs are used to diagnose dislocations of the shoulder (see Image 1) and can depict the following:

• Presence of a Hill-Sachs lesion (see Image 2)
• Subglenoid new bone formation
• Presence of bony abnormality of the anterior or posterior rim
• Presence of fractures (see Image 3)
• Degenerative changes in the joint

Radiographs help not only in making the diagnosis but also in determining whether the changes might improve with treatment.

The anteroposterior, internally rotated view is useful for demonstrating the presence and size of a Hill-Sachs defect. Special projections, including the modified Didiee, Hermodsson, Stryker, and West Point views, have been developed to increase the sensitivity of radiography in detecting the lesions. The West Point axillary view is useful for identifying the extent and presence of a Hill-Sachs lesion when it is not seen on anteroposterior, internally rotated, and Y-scapular or axillary views.

Posterior dislocation and instability

• Loss of the humeral head and glenoid rim bony parallelism (crescent sign) may be observed.
• Posterior dislocation also produces findings of glenoid rim fractures, bony fracture, sclerosis, or ectopic bone formation.
• A compression of the anteromedial humeral head may be seen as a reverse Hill-Sachs lesion (trough sign). A trough sign resulting from impaction fracture of the humeral articular surface onto the osseous glenoid has been described (see Image 4).
• Avulsion fracture of the lesser tuberosity may be visualized.
• Interruption or peaking of the Maloney arc, a line drawn along the lateral border of the scapula and down the medial aspect of the humerus, has been described.

Luxatio erecta

The humeral head is dislocated inferiorly to a subcoracoid position. The superior aspect of the humeral head does not contact the inferior aspect of the glenoid rim, and the arm is held over the patient's head in a fixed abducted position. An associated fracture of the greater tuberosity may be present (see Image 5).

Degree of Confidence

To the authors' knowledge, no group reports a single rate (even as an estimate) of anterior instability; however, a Hill-Sachs lesion is seen in approximately 50% of radiographs in patients with anterior instability, and other osseous lesions are seen in 10-15% of radiographs.

Computed Tomography

Findings

The introduction of CT arthrography allowed imaging of the capsular elements and improved visualization of the labrum. This technique improved demonstration of the articular and synovial surfaces, the long head of the biceps tendon, and intra-articular loose bodies. CT can help in determining the direction of instability and the nature of capsulolabral complex injury after an acute episode of trauma. Furthermore, complications of posttraumatic dislocation (ie, osteonecrosis) may be detected on CT scans. CT arthrography can demonstrate the major causes of instability (ie, bony, cartilaginous labral, capsular, ligamentous, or tendinous causes).^{7,9,21,28,29,26,30,15,31,2,6}

The patient is most commonly in the supine position during CT scanning, with the arm in neutral rotation. However, imaging in the prone oblique position has been reported to be superior to imaging in the standard supine position. This position allows both the anterior and the posterior capsulolabral complex to be outlined by air.

Anterior instability

• The cartilaginous labrum can be seen to be partially detached from the bony glenoid.
• The labrum may be shredded and torn, degenerated, or even absent (see Image 6).
• Torn or degenerated labrum may be seen as an area of imbibition of contrast medium.
• Thickening of the labrum is an abnormal finding on CT arthrography.
• Capsular injury may be detected (see Image 7).
• CT findings include irregularity of the scapular insertion site, indicating swelling and hemorrhage in the acute stage.
• In addition, acute capsular tears are evident because of extravasation of contrast medium or capsular redundancy.
• Ectopic calcification and ossification resulting from rupture of the scapular periosteum often are seen in the chronic stage.
• Injury to the capsule may be subtle, although in some patients, detachment is pronounced and stripped medially to the scapular neck.
• The subscapularis bursa extends medially beneath the coracoid process, and the opacified bursa normally forms a sharp transition with the scapular attachment of the capsule at or above the glenoid notch.
• Stripping of the capsule in anterior instability results in loss of the boundary, and a large recess is formed over the scapular neck, which is well demonstrated using conventional double-contrast arthrography. As previously mentioned, this finding is not well correlated with anterior instability.
• Loose bodies are visualized as filling defects in the joint space that are outlined completely by contrast material (see Image 8).
• Subscapularis muscle abnormalities are seen as tears and areas of irregularity.
• Bony lesions, such as Hill-Sachs defects and fracture of the anterior glenoid rim (bony Bankart lesion), are readily visualized (see Images 9-10).
• A Bennett lesion may be seen and appears as a crescent of mineralization on the axillary radiographic view. It is better seen on CT scans.

Posterior instability

• CT findings in posterior instability include a Bankart-like lesion, tearing or shredding of the labrum, and capsular tear. However, tearing or shredding of the labrum may be the only finding.
• Findings are typically the reverse of the findings seen in anterior instability.
• Multidirectional instability resulting from previous injury usually is more prominent in 1 direction.
• In repeat microinjury (eg, due to swimming or a congenital condition), the labrum is usually attenuated and degenerated.
• The joint capsule may be redundant.
• Capsular laxity associated with multidirectional instability is diagnosed by capsular abnormalities in at least 2 directions, usually the anterior and posterior aspects.
• Scans obtained with the patient's arm externally rotated may demonstrate posterior lesions more clearly than other scans. Bankart lesions usually are not seen.

Degree of Confidence

Conventional CT can better define all the bony abnormalities that may be missed or seen less clearly on radiographs. In addition, CT arthrography can demonstrate labral and capsular lesions.

CT arthrography has a sensitivity of approximately 73% for detecting lesions of the capsuloligamentous complex, glenoid labrum, intracapsular portion of the long head of the biceps tendon, and rotator cuff.

False Positives/Negatives

Most errors in image interpretation arise because of faulty injection technique. The capsule may be distorted by extracapsular injection or injection into the substance of the capsule. Forceful injection of contrast material into the labrum can result in localized accumulation of contrast medium, and this can simulate a tear.

Magnetic Resonance Imaging

Findings

MRI findings can be divided into those demonstrated on conventional MRIs and those demonstrated on MR arthrograms.^1,2,3,4,5,6

Conventional MRI

Anterior instability

• The primary finding of a Bankart lesion on axial MRIs is a zone or band of abnormal signal intensity, which is increased on proton density–weighted images, T2-weighted images (T2WIs), and T2*-weighted images (T2*WIs). This zone separates the anteroinferior capsulolabral complex from the osseous glenoid margin (see Image 11).
• If the dislocation is recent, an effusion is often present, and detachment of the labroligamentous complex may be visualized.
• Axial T1-weighted images (T1WIs) or T2WIs may show subchondral bone changes, which demonstrate low signal intensity on T1WIs and high signal intensity on T2WIs.
• Small separations, called partial Bankart lesions, may appear to involve the glenoid labrum alone on axial images. These are more likely to be associated with subluxational instabilities.
• In chronic recurrent instability, the labrum degenerates and is likely to be markedly diminished in size or to be totally absent.
• In long-standing lesions, in which the labrum is reapproximated in its normal position and granulation tissue forms, a zone of intermediate intensity is observed separating the capsulolabral complex from the glenoid on proton density–weighted images and T2*WIs. When seen on MRI, this pattern is a highly accurate indicator of a healed Bankart lesion.
• Linear tears of the labrum substance or deformity of the labrum may be observed to be damaged by the impact of the humeral head.
• Increased signal intensity of the anteroinferior labrum substance after acute injury or in the recurrent stage represents edema, granulation tissue, or labrum degeneration.
• Despite the poor definition of the labrum in the absence of an effusion, signal alterations in the signal intensity of the capsulolabral complex at the glenoid junction are demonstrated well on proton density–weighted images and gradient-echo images.

A classification system for abnormal labral intensity has been formulated for conventional MRI as follows:

• Type 1 - Increased signal with no surface extension, representing internal degeneration without tear.
• Type 2 - Blunted or frayed labrum with normal dark intensity.
• Type 3 - T1 or T2 signal extends to the surface.
• Type 4 - This is a combination of abnormal morphology with type 2 features and increased signal intensity extending to the surface with type 3 features.

A useful finding for separating an acute Bankart lesion from a chronic one is increased signal intensity in the subchondral bone on fat-suppressed, fast spin-echo T2WIs or short-tau inversion recovery (STIR) images.

Capsular lesions are well depicted, but only if an effusion is present. The capsule is often wavy or stripped from the periosteum, and it is an accurate indicator of a stretched or redundant capsule. In the subacute stage, irregularity of the joint capsule with intermediate signal intensity is observed. After the acute soft-tissue changes resolve, the capsule and capsular ligaments fold over, producing an area of low signal intensity. A region of signal void is also seen in ectopic bone formation.

Osseous lesions are seen as areas of decreased signal intensity on T1WIs, and they may be relatively bright on T2WIs (see Images 12-13). Hill-Sachs lesions are evaluated best at the level of the coracoid process and range in appearance from mild flattening to wedge-shaped defects of the humeral contour. Conventional MRI is superior to CT arthrography for evaluating these lesions. ALPSA, Perthes, and HAGL lesions cannot be detected reliably on conventional MRI, and arthrography is recommended.

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 Fibrosing Dermopathy. 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 magnetic resonance angiography 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.

Posterior instability

Using conventional MRI, findings related to posterior instability are typically the reverse of those for anterior instability. The labrum is usually detached, frayed, or torn. On conventional MRIs, the changes associated with anterior stability can also be used to identify the labral abnormalities of posterior instability.

The disruption of the posterior capsule is seen as a disruption or marked irregularity of the normal, continuous, hypointense line extending from the glenoid rim to the neck of the humerus.

Soft-tissue injury is visualized as an area of increased signal intensity in the soft tissues in the posterior area on T2WIs; this finding represents edema, hematoma, or extravasation of joint fluid. Discontinuity of the hypointense teres minor tendon and reverse Hill-Sachs lesion are easily demonstrated.

MR arthrography

The GHLs are best visualized when a joint effusion is present. The presence of fluid outlines the avulsed labral fragment clearly. Arthrography can be achieved by using a sodium chloride solution, direct dilute gadopentetate dimeglumine administration, or indirect gadopentetate dimeglumine administration.

Patients with acute injury usually do not require arthrography, because the effusion that is present is often adequate. Patients who benefit most are young athletic individuals with the chronic, milder forms of instability. Therefore, MR arthrography is used more often in these patients and in patients in whom nonenhanced studies fail to address the clinical situation.

With MR arthrography, imaging patients in the ABER position to detect anterior labral tears provides a sensitivity of 89% and a specificity of 95% compared with 48% and 91%, respectively, in the normal neutral position. In the ABER position, the patient's arm is elevated, and the palm is placed under his or her neck.

With direct arthrography, dilute gadopentetate dimeglumine (concentration of 2 mmol/L mixed in normal sodium chloride solution) is injected into the shoulder, usually via an anterior approach. Approximately 12-20 mL of dilute gadopentetate dimeglumine is used.

The shoulder may be exercised gently and passively before imaging. Reasonable distention of the contrast material is usually achieved for as long as 1 hour, but this duration can be extended if 0.3-1.0 mL of 1:1000 of adrenaline also is administered into the joint.

The capsular anatomy, GHLs, and the anterior and posterior labrum are best visualized in the axial plane. The superior and inferior labrum and the axillary pouch are better visualized in the coronal plane. The sagittal plane demonstrates the entire capsule, including the orientation of the GHLs, to best advantage.

Anterior instability

• Labral lesion- Labral tears are visualized as contour deficiencies of the labrum, filling of a torn labrum with contrast material, and opacification of the space between the detached labrum and the glenoid surface (see Image 14).
• Bankart lesion - On MR arthrograms, the Bankart lesion is seen as a fragment of labrum attached to the anterior band of the IGHL and to the ruptured scapular periosteum floating in the anteroinferior aspect of the glenohumeral joint (see Image 15).
  • Axial images are more useful in demonstrating the morphology of the labrum and associated tear pattern, if present. Coronal oblique images show avulsion of the anteroinferior labrum and its relationship to the axillary pouch, which is lax when the arm is adducted. Sagittal oblique images define the size of the anteroinferior glenoid fracture and the extent of the labral tear both anterosuperiorly and superoinferiorly.
  • The relationship of the anterior band of the IGHL to the avulsed labrum is identified at the level of the glenoid fossa on axial and oblique sagittal MRIs (see Image 16).
• ALPSA lesion - Identifying an ALPSA lesion is desirable because the surgical treatment is different from that for a Bankart lesion. On axial MR arthrograms, the anterior labrum with stripped periosteum is seen to be displaced medially and rotated inferiorly on the neck of the glenoid (see Image 17).
  • A small cleft or separation can be seen between the glenoid margin and the labrum. In chronic lesions, the labrum is abnormally thickened and flattened because of healing, with synovial tissue between the labrum and the glenoid margin.
• Perthes lesion - If labroligamentous avulsion occurs with an intact scapular periosteum and if the periosteum is stripped medially, becoming redundant, the lesion is called a Perthes lesion (see Image 18). A Perthes lesion is distinguished from an ALPSA lesion by the redundant periosteum versus the rolled-up, medially displaced periosteal labral mass. A Perthes lesion can be difficult to see during arthroscopy if the labrum reapproximates its normal position and is resynovialized; its appearance may be normal on conventional MRIs.
  • Imaging in the ABER position by stretching the inferior glenoid ligament and its labral attachment can aid visualization of the abnormality. In ABER positioning, labroligamentous detachment is evident by visualizing the contrast medium separating the labrum from the glenoid rim.
• HAGL lesion - The HAGL lesion refers to avulsion of the IGHL from the humerus, without accompanying tear of the subscapularis. This lesion has not been shown to demonstrate an age predilection. The HAGL lesion may exist in patients with anterior instability with or without an anterior labral tear and still cause instability. The lesion is treated with surgical reattachment of the IGHL to its humeral insertion. An effusion or arthrography is usually required to visualize the lesion.
  • On oblique sagittal images, the retracted or redundant IGHL appears as a mass of low signal intensity. As the IGHL drops inferiorly, the axillary pouch is converted from a fluid-distended, U-shaped pouch to a J-shaped structure.
• GLAD lesion - On MR arthrograms, a superficial tear of the anteroinferior labrum is seen. The anterior glenoid has a chondral defect, which is filled with gadolinium. The labrum remains attached to the anterior scapular periosteum, distinguishing this from a Bankart lesion, which has torn periosteum (see Image 19).
• Ligamentous lesions - Isolated GHL tears are best visualized by using MR arthrography. Signs include thickening, a wavy and irregular contour of the GHL, and increased signal intensity. The IGHL is considered abnormal if it is absent, discontinuous, attenuated, or attached to the scapular neck medial to the glenoid rim.
  • MR arthrography has been shown to be effective in detecting loose bodies in the shoulder (see Image 20). Loose bodies usually are hypointense on T1WIs and on T2WIs and lie in a dependent position.
• Bennett lesion - This appears as a low signal intensity band posterior to the posterior labrum on the axial images (crescentic mineralization). Due to calcification, there is thickening and low signal of the posterior capsule/posterior limb of the inferior GHL. The adjacent labrum is normal.
• Osseous lesion - Axial T1WIs show subchondral bone changes, including low–signal-intensity sclerosis or marrow edema at the fracture site. Hill-Sachs lesions produce changes similar to those seen on conventional MRIs. Crescentic extra-articular ossification may be demonstrated on CT scans or MRIs.
  • Associated reactive, anteroinferior glenoid rim sclerosis may exist. MRI findings include low–signal-intensity calcification. Ossification may not be identified arthroscopically because of its extra-articular location.

Posterior instability

Findings are typically the reverse of the findings seen in anterior instability. Appearances on MR arthrography include all those found on conventional MRI findings, as well as extravasation of contrast material into the soft tissue behind the shoulder joint.

Tearing or shredding of the posterior glenoid labrum may be seen. Capsular detachment or stripping is less common. Capsular tear and disruption of the posterior cuff may occur with more severe injuries and may result in formation of a subcapsular synovial recess. Glenoid margin erosions, sclerosis, or ectopic bone formation may be seen.

Axial MRIs usually demonstrate the posterior labrum disruption well (see Image 21). The abnormal laxity or redundancy of the torn posterior capsule also may be seen on axial images. The humeral head is often also subluxed posteriorly relative to the glenoid fossa. MR arthrography demonstrates posterior contrast extension into the planes between the posterior labrum, the capsule, and the infraspinatus muscle.

Degree of Confidence

Conventional MRI has been reported to have sensitivities of 67-86% and specificities of 44-95% in the diagnosis of glenoid labral tears. MR arthrography has been reported to have sensitivities of 90-95% and specificities of 67-86%.

MR arthrography is more accurate than CT arthrography for evaluation of the capsuloligamentous complex, glenoid labrum, intracapsular portion of the long head of the biceps tendon, rotator cuff, and osseous lesions.

False Positives/Negatives

Common variants may simulate labral lesions, including the sublabral foramen, Buford complex, and hyaline cartilage undercutting of the labrum.

A sublabral foramen located between the labrum and glenoid rim is a frequent cause of misinterpretations of anterior labral disruptions or tears. This has been reported to occur in as many as 11% of individuals. In contrast to a Bankart lesion, the sublabral foramen is seen superior to the anterior glenoid notch or above the physeal line representing the superior one third of the glenoid.

Bankart lesions usually involve the labral tear or avulsion at or below the level of the subscapularis tendon. This is located below the physeal line or equator (the physeal line divides the bony glenoid into an upper one third or lower two thirds corresponding to the 2 glenoid ossification centers).

The Buford complex consists of 3 elements, as follows:

• Cordlike MGHL
• MGHL that attaches directly to the superior labrum anterior to the biceps (at base of biceps anchor)
• Absent anterosuperior labrum

The incidence of Buford complex is approximately 1.5%. The cordlike MGHL attaches directly to the superior labrum. Distinguishing a Bankart lesion from a Buford complex is easy because in the former, the anteroinferior labrum is torn or avulsed and does not appear firmly attached to the anteroinferior glenoid rim.

In hyaline cartilage undercutting of the labrum, articular cartilage is present between the labrum and the glenoid bony cortex, predominantly in the superior half of the joint. This interface can simulate a labral tear on axial images. In general, superior labral tears are oriented laterally, while the cartilage interface is oriented parallel to the glenoid cortex. Variation in size and morphology of the labrum remains a source of error. A small labrum may not be distinguishable from a mildly degenerated and deficient labrum.

Some anatomic variations that are differentiated easily with MR arthrography present diagnostic pitfalls with conventional MRI. Normal, intermediate – signal-intensity labral fibrocartilage at the base of the anterior labrum rarely presents a problem, because the cartilage has signal intensity lower than that of the contrast medium. Normal GHLs often can simulate torn labral fragments on conventional MRIs. With MR arthrography, intact GHLs can be visualized to be separate from the labral origins of the distended capsule, and these are not confused with torn fragments.

The sublabral sulci that normally fill with contrast medium remain a diagnostic pitfall and cannot be differentiated from labral tears unless the labrum is separated from the glenoid rim. Sublabral sulci involve the interface of the labrum with the articular cartilage and are located at the labral-bicipital junction or between the origins of the MGHLs and IGHLs. Complete labral detachment (sublabral hole) may also represent a normal variant.

Glenohumeral joint alterations, including ALPSA, Perthes, and HAGL lesions, cannot be diagnosed reliably by using conventional MRI. MR arthrography is better than MRI in the detection of capsular redundancy.

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