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Dr/ ABD ALLAH NAZEER. MD.Radiological imaging of shoulder dislocation.

Shoulder dislocationIn ashoulder dislocation,there is separation of the humerus from the glenoid of the scapula at the glenohumeral joint.This article contains a general discussion on shoulder dislocation. For specific dislocation types please refer to the following articles:anterior shoulder dislocation(95%)posterior shoulder dislocationinferior shoulder dislocationEpidemiology:Sex distribution is bimodal and relative incidence is dependant on patient age. Younger patients tend to be male and injury is often related to sporting trauma:younger: 20-30 (male to female ratio of 9:1).older: 60-80 (female to male ratio of 3:1).

Clinical presentationPatients present with severe pain and restriction of movement of the shoulder.The majority of people who present with a shoulder dislocation do so after trauma, e.g. sporting trauma, assault,seizure, falls.It is useful to determine whether the dislocation is acute,chronic or recurrent.PathologyEtiologyThe shoulderis exceptionally maneuverable and sacrifices stability to enable an increase in function. It is vulnerable to dislocation, and is the most commonly dislocated large joint. Approximately half of major joint dislocations seen in emergency departments are of the shoulder.Shoulder dislocation almost exclusively occurs following trauma. The shoulder is in its weakest position when it is abducted and externally rotated.Sporting injuries and motor vehicle collisions are common causes.Increased incidence in patients who have had previous shoulder injury, and particularly in those who have dislocated previously.The process of dislocation is massively disruptive to the labrum, joint capsule,supporting ligaments and muscles. This is particularly true in anterior dislocations where there can be injury to the anterior capsule, anterior labrum or biceps tendon.

Type of dislocationShoulder dislocations are usually divided according to the direction in which the humerus exits the joint:Anterior> 95%.subcoracoid (majority).subglenoid (1/3).subclavicular (rare).Posterior2-4%. Inferior (luxatio erecta) < 1%.

Radiographic featuresA shoulder x-ray series is sufficient in almost all cases to make the diagnosis, although CT and MR are often required to assess for the presence of subtle fractures of the glenoid rim or ligamentous / tendinous injuries respectively.Plain radiographAnterior and inferior dislocations are usually simple diagnoses, with the humeral head and outline of the glenoid being incongruent.Where the humeral head is displaced medially and overlies the glenoid, the dislocation is anterior.Posterior dislocations can be difficult to identify on an AP view only (as may be obtained in the setting of secondary survey of a trauma) as the humeral head moves directly posteriorly and congruency may appear to be maintained (at least at first glance).All dislocations should be easily identified on trans-scapular Y views. When the humeral head is normally aligned, it will project centered over the centre of the Y formed by the coracoid, blade of the scapula and spine of the scapula (acromion).

Inferior Shoulder Dislocation.

Normal glenohumeral joint.An anterior shoulder dislocation.

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 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.

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 instabilityCT 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 micro injury (e.g., 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 confidenceConventional 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.

Double-contrast axial computed tomography (CT) arthrogram of the left shoulder shows an undisplaced tear (arrows) of the anterior glenoid labrum. The patient had one episode of an anterior dislocation.

Double-contrast axial computed tomography (CT) arthrogram of the right shoulder shows a deficient anterior glenoid labrum (arrows) and medial stripping of the anterior capsular attachment (arrowhead). The patient had a recurrent anterior dislocation.

Double-contrast axial computed tomography (CT) arthrogram of the right shoulder shows a small, loose body (arrow) in the axillary recess. The patient had recurrent anterior dislocations.

Double-contrast, reconstructed, 2-dimensional coronal computed tomography (CT) arthrogram of the right shoulder shows a large Hill-Sachs defect (arrow) in the humeral head. A full-thickness rotator cuff tear is present, evidenced by a large amount of air in the subacromial/subdeltoid bursa. The remnant end of the supraspinatus tendon is seen (arrowhead).

Double-contrast axial computed tomography (CT) arthrogram of the left shoulder shows a bony Bankart glenoid fracture (arrows). The patient had one episode of an anterior dislocation.

MRI findings can be divided into those demonstrated on conventional MRIs and those demonstrated on MR arthrograms.Anterior instability on conventional MRIThe primary finding of a Bankart lesion on axial MRIs is a zone or band of abnormal signal intensity, which is increased on proton densityweighted images, T2-weighted images (T2WIs), and T2*-weighted images (T2*WIs). This zone separates the anteroinferior capsulolabral complex from the osseous glenoid margin 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 densityweighted 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 densityweighted 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 the images below). 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). 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.Posterior instability on conventional MRIUsing 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 overviewThe 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 on MR arthrographyLabral 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 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 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 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 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.

Posterior instability on MR arthrographyFindings 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 the image below). 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.

Axial, fat-suppressed, spin-echo T1-weighted magnetic resonance arthrogram of the right shoulder shows an undisplaced tear (arrow) of the anterior glenoid labrum. Part of the middle glenohumeral ligament is shown (arrowhead). The patient had one episode of anterior dislocation.Axial, spin-echo T1-weighted magnetic resonance arthrogram of the left shoulder shows a deficient anterior labrum (arrows) and medial stripping of the anterior capsular attachment (arrowheads). The patient had recurrent anterior dislocations.

Coronal, T1WI and fast spin-echo T2-weighted conventional magnetic resonance imaging (MRI) scan of the left shoulder shows a large Hill-Sachs defect (arrows) in the superolateral humeral head. Surrounding bone marrow edema is shown. Fluid is present in the subacromial/subdeltoid bursa (arrowheads), indicative of a full-thickness rotator cuff tear. The patient had one episode of an anterior dislocation.

Coronal, fat-suppressed, spin-echo T1-weighted magnetic resonance arthrogram image of the right shoulder shows a loose body (arrow) in the axillary recess. The patient had a previous dislocation.

Axial, spin-echo T1-weighted magnetic resonance arthrogram of the right shoulder shows an undisplaced tear (arrow) of the anterior glenoid labrum, which remains attached to the inferior glenohumeral ligament (arrowhead). The patient had recurrent anterior dislocations.

Axial, spin-echo T1-weighted magnetic resonance arthrogram of the right shoulder shows an anterior labroligamentous periosteal sleeve avulsion lesion (arrows), seen as a rolled-up mass anterior to the neck of the scapula. The patient had recurrent anterior dislocations.

MR images in a 31-year-old male dancer obtained 4 days after acute first-time anterior shoulder dislocation.A, Oblique coronal fat-suppressed T2-weighted image shows a small Hill-Sachs fracture (arrow) with prominent bone marrow edema. Effusion is present.B, On more anterior oblique coronal fat-suppressed T2-weighted image, the inferior labral-ligamentous complex (open arrow) is detached and displaced from the inferior glenoid rim. The humeral attachment site (solid arrow) is unremarkable. The cuff is intact.C, On axial gradient-echo image, the anteroinferior labral-ligamentous complex (open arrow) is displaced from the glenoid rim, and the attached periosteum (solid arrow) is stripped medially along the glenoid neck. No glenoid rim fracture is present.

Acute first-time anterior shoulder dislocation: T1-weighted MR images in a 26-year-old man with shoulder pain after a single anterior dislocation. MR arthrography was performed 2 months after known dislocation owing to persistent pain and limitation.A, Axial fat-suppressed image demonstrates an intact anterior labrum (arrow).B, ABER image demonstrates an avulsion of the anterior labrum with an intact glenoid periosteum and capsule (arrow), highlighting the mechanical advantage of having the shoulder in this position during imaging.

MR images of acute ALPSA in a 24-year-old man who sustained a first episode of anterior shoulder dislocation 3 weeks prior to imaging.A, Fat-suppressed T2-weighted and,B, axial fat-suppressed intermediate-weighted images demonstrate a Hill-Sachs lesion (white arrow) with marrow edema and associated anteroinferior labral tear with anteromedially displaced fragment (open arrow). Note stripping and edema of the scapular periosteum with developing granulation tissue (black arrow).

MR images of acute recurrent anterior shoulder dislocation with Bankart fracture in a 64-year-old man.A, Sagittal and,B,C, coronal fat-suppressed T2-weighted images demonstrate extensive periarticular posttraumatic swelling () with high-grade partial thickness tears of the subscapularis myotendinous junction (white arrow) and humeral muscular insertion (open arrow) as well as strains of the supraspinatus(SST), infraspinatus(IST), teres minor(Tmi), latissimus dorsi(LD), triceps(T), and teres major(Tma)muscles. Glenohumeral and subacromial subdeltoid effusions (), as well as humeral avulsion of the inferior glenohumeral ligament (HAGL ) and a detached and mildly displaced Bankart fracture (black arrow).D, Sagittal T1-weighted image demonstrates a displaced Bankart fracture fragment. The defect in the anteroinferior glenoid rim is somewhat ill defined.E, Three-dimensional MR reconstruction demonstrates the amount of glenoid bone loss, glenoid fracture margin (white arrow), and adjacent fracture fragment (open arrow) to a better extent than the conventional MR images.F, Three-dimensional MR reconstruction of the humeral head demonstrates a mildly displaced avulsion fracture of the greater tuberosity at the insertion of the supraspinatus tendon (black arrow), as well as an impacted Hill-Sachs lesion (white arrow).

Chronic multidirectional instability in a 41-year-old woman with apprehension, disability, and provocative testing positive for instability and without previous dislocation or major traumatic event. At conventional MR imaging of the shoulder 5 weeks earlier at an outside institution, findings were interpreted as negative for labral-ligamentous injury. On this oblique coronal fat-suppressed T1-weighted arthrographic MR image, contrast material outlines the anterior band of the inferior glenohumeral ligament (black arrow), which is ruptured and retracted from its humeral attachment site. Contrast material leaks from the joint into the quadrilateral space (white arrow). Capsulorrhaphy was performed arthroscopically.

Chronic ALPSA in a young baseball player with clinical findings of anteroinferior instability and no history of prior dislocation.A,B, Axial and,C, sagittal fat-suppressed T1-weighted MR arthrograms demonstrate a medially displaced anteroinferior labral tear (black arrows) and stripped off scapular periosteum with scar tissue annealing the fragment and periosteum to the inferomedial scapular neck (white arrows).

MR images in a 24-year-old extreme athlete who denied previous dislocation or major shoulder trauma. A, Axial, fat-suppressed T1-weighted MR arthrogram shows increased signal intensity at the labral chondral junction (black arrow), as well as a nondisplaced posteroinferior labral tear and a contrast agentfilled chondral defect with a GLAD lesion (white arrow). A small subchondral cyst is found adjacent to the posterior tear (open arrow).B, On ABER fat-suppressed T1-weighted MR arthrogram, tear of the anteroinferior labral chondral is made conspicuous (arrow). At the time of initial MR imaging, the patient elected to continue competition, forgoing surgical intervention. Repeat MR imaging 2.5 years later was performed due to disability preventing further competition. C, Axial fat-suppressed T1-weighted MR arthrogram shows a Bankart lesion and marked displacement of the anteroinferior labral-ligamentous complex (arrow) from the glenoid rim.D, ABER fat-suppressed T1-weighted MR arthrogram demonstrates progression to a GLAD injury in the anteroinferior labrum with detachment and displacement of a large labral chondral fragment (arrow). Arthroscopic stabilization procedure was performed. The posteroinferior labral chondral GLAD lesion appears to have healed in the interval.

(A-C): Bony Bankart lesion in a 28-year-old male with recurrent anterior shoulder dislocation. Axial TSE T1W fat-saturated MRA image (A) shows an absent anteroinferior labrum with bony injury (arrow). Sagittal TSE T1W fat-saturated MRA (B) and sagittal MRA image (C) 5 mm medial to B, show the full extent of the bony Bankart lesion (arrow).

(A-C): Perthes lesion. A 16-year-old male presented with post-traumatic recurrent anterior shoulder dislocation. TSE T1W fat-saturated axial MRA image (A) and TSE T1W fat-saturated oblique axial MRA image with arm in ABER position (B) show intercalation of intra-articular contrast beneath the anterior labrum (small arrow) with an intact scapular periosteum (long arrow); this suggests a diagnosis of Perthes lesion. TSE T1W fat-saturated oblique sagittal MRA image (C) shows the extent of the lesion (arrows).

ALPSA lesion in three different patients with anterior shoulder instability. TSE T1W fat-saturated coronal MRA images (A,B) and axial MRA image (C) show the anteroinferior labrum and antero-inferior glenohumeral ligament rolled back medially along the scapular neck (arrow)

GLAD lesion in an 18-year-old male student. TSE T2W fat-saturated axial conventional MRI image (A) and coronal TSE T1W fat-saturated MRA images (B,C) show anterior-inferior labral injury (long arrow) with an articular cartilage defect (small arrow).

(A-B): Coronal TSE T1W MRI (A) and axial TSE T1W fat-saturated MRA (B) images show a comminuted greater tuberosity fracture (arrow) in this 38-year-old male presenting with traumatic shoulder instability

(A-B): Reverse Hill-Sachs and reverse Bankart lesion in a 34-year-old male who had multidirectional instability with a posterior dislocation at presentation. Axial TSE T1W fat-saturated MRA images (A,B) show a reverse Hill-Sachs lesion (long arrow) as a bony defect in the anterior humeral head. A posterior labral tear is indicated with a thick arrow. The patient also had an anterior labral tear (small arrow in B) and a Hill-Sachs lesion from previous anterior dislocations. A Bennett lesion is seen as ossification, posteriorly along the scapular neck (long arrow in B)

Morphologic abnormality of the posteroinferior glenoid in a patient with posterior instability. Axial GRE MEDIC T2W MRI image (A) and axial CT arthrogram image (B) reveal the "lazy J" deformity; better appreciated on CT scan

MRI of shoulder after dislocation with Hill-Sachs lesion and labral Bankart's lesion.

Dual post-traumatic findings - Note the presence of both a Hill-Sachs deformity of the posterolateral humeral head and a partial thickness supraspinatus tendinous tear.

Combined tendinous injuries from a single, devastating shoulder injury. Displaced tendon of long head of biceps muscle (Fig A), Subscapularis tendinous avulsion and Teres minor tendon partial tear (Fig B), Posterior capsular disruption (Fig C) and Supraspinatus tendinous disruption (Fig D).

Bankart and Hill-Sachs lesions in anterior shoulder dislocation. (A) T1-weighted oblique coronal and (B) STIR axial MR images of the shoulder show a bony Bankart lesion with detachment of the anteroinferior labrum from the underlying glenoid, involving the bony margin (impaction fracture) (arrows). STIR axial (C) and oblique sagittal (D) MR images show a Hill-Sachs lesion with posterolateral humeral head compression fracture with bone edema as the humeral head comes to rest against the anteroinferior part of the glenoid. These types of lesions frequently occur in collision-sports

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