You are in: eMedicine Specialties > Radiology > MUSCULOSKELETAL Shoulder, DislocationsArticle Last Updated: Jun 21, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 9
  Author: Gavin Yeh Tseng, MBBS, FRCR, FAMS, Consultant Radiologist, Department of Diagnostic Radiology, Raffles Hospital Gavin Yeh Tseng is a member of the following medical societies: Royal College of Radiologists Coauthor(s): Wilfred CG Peh, MD, MBBS, FRCP(Glasg), FRCP(Edin), FRCR, MHSM, Clinical Professor, Faculty of Medicine, National University of Singapore; Senior Consultant Radiologist, Programme Office, Singapore Health Services Editors: David S Levey, MD, PhD, Orthopedic/Spine MRI TeleRadiologist, Radsource, LLC; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; William R Reinus, MD, MBA, FACR, Professor of Radiology, Temple University; Chief of Musculoskeletal and Trauma Radiology, Vice Chair, Department of Radiology, Temple University Hospital; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Felix S Chew, MD, MBA, EdM, Professor, Department of Radiology, Vice Chairman for Radiology Informatics, Section Head of Musculoskeletal Radiology, University of Washington Author and Editor Disclosure Synonyms and related keywords: glenohumeral instability, atraumatic shoulder dislocation, congenital shoulder laxity, macrotraumatic shoulder dislocation, microtraumatic shoulder dislocation, recurrent shoulder dislocation, Bankart lesion, atraumatic type with multidirectional and bilateral instability, AMBRI, glenohumeral ligaments, anterior shoulder dislocations, posterior shoulder dislocations, anterior labroligamentous periosteal sleeve avulsion, ALPSA, humeral avulsions, glenoid labral articular disruption, GLAD, bony humeral avulsion of the glenohumeral ligament, BHAGL, Perthes lesion, luxatio erecta, inferior shoulder dislocation INTRODUCTIONSection 2 of 9
  BackgroundThe shoulder joint is inherently unstable, and injury to the shoulder is commonly encountered. Shoulder dislocations can be classified either as an acute single event or as recurrent episodes (glenohumeral instability). Glenohumeral instability can be classified further by underlying causes: atraumatic (congenital laxity), macrotraumatic (resulting from an event), and microtraumatic (repetitive injury). They can also be categorized by the various degrees of subluxation or dislocation. Other subdivisions include direction and voluntary/involuntary mechanisms. A first-time acute shoulder dislocation may also represent the initial presentation of recurrent dislocation. Patients can be classified into the following 2 clinical categories, which represent the 2 ends of a broad spectrum:
Traumatic anterior glenohumeral instability accounts for 95% of glenohumeral instability seen in clinical practice. For excellent patient education resources, visit eMedicine's Breaks, Fractures, and Dislocations Center. Also, see eMedicine's patient education article Shoulder Dislocation. PathophysiologyStability of the glenohumeral joint is maintained by passive and active mechanisms.
The vacuum effect may be disrupted by avulsion, rupture, or stretching by injury. The labrum accounts for 50% of the socket area of the joint; therefore, loss of labrum can reduce the socket depth substantially. Repairing labral detachments, such as Bankart lesions, is important because labrectomy in the mildly unstable glenohumeral joint may lead to progressive symptomatic deterioration and instability. Dislocation often occurs because of these anatomic characteristics and because of the frequency of injuries to the shoulder region. The 3 glenohumeral ligaments (GHLs) represent condensations of the shoulder capsule and are variable in appearance on imaging. The ligaments act to strengthen the joint capsule and course from the humerus to their glenoid attachments. The capsule and its insertions are depicted well on MRIs. The posterior capsule always inserts into the posterior labrum. The anterior capsule has a more variable medial insertion. The 3 types of anterior capsule insertion have been described as follows:
Most capsules are inserted anteriorly on the labrum (47%) or glenoid neck (49%). In the past, anterior capsular insertions of the shoulder were regarded as being contributory toward shoulder instability, but studies have shown that the different types of capsular insertions are statistically similar in both stable and unstable shoulders. Furthermore, capsular abnormalities have little role in influencing surgical treatment. Anterior dislocation Anterior dislocations are usually the result of direct or indirect trauma, with the arm forced into abduction and external rotation. This is by far the most frequent type of shoulder dislocation and represents more than 90% of injuries. Of single acute dislocations, 40% become recurrent as a result of associated damage of the surrounding ligamentous and capsular structures that stabilize the joint. The most important structure stabilizing the shoulder—one that limits gross anterior-inferior subluxations and dislocation—is the IGHL. This ligament forms a sling with discrete anterior and posterior bands. It is lax when the humerus is in the neutral position, and it allows normal shoulder movement. The ligamentous complex becomes taut in abduction and external rotation and, thus, stabilizes the joint at the end range of shoulder movement in the abduction external rotation (ABER) direction. During a dislocation, forces exceed the threshold that the ligamentous complex can bear, leading to tears or stretching. This may lead to laxity and instability. Failure of the IGHL can occur at the insertion site (40%), in the ligamentous substance (35%), and at the humeral insertion site (25%). Avulsions are seen more frequently in the anterior band and the anterior aspect of the axillary pouch, whereas ligamentous substance tears are more common in the posterior aspect of the axillary pouch. Bankart lesions represent failure of the IGHL at the glenoid insertion. IGHL capsule laxity represents intrasubstance ligamentous failure, whereas humeral avulsions of the GHL (HAGL) represent failure of the IGHL at its humeral insertion. The MGHL is often absent or underdeveloped and plays a minor role. Tears of the GHL can occur without associated labral tears and also can cause shoulder instability. The following lesions may be seen in anterior dislocation:
A subset of these lesions, initially were defined using arthroscopy (ie, anterior labroligamentous periosteal sleeve avulsion [ALPSA] lesion, Perthes lesion, glenoid labral articular disruption [GLAD], HAGL lesion) but are also well demonstrated by magnetic resonance (MR) arthrography. Regarding labroligamentous lesions, in 1938, Bankart identified an "avulsed fibrous and fibrocartilaginous fragment" from the glenoid margin as the essential lesion of recurrent shoulder dislocation and described a highly successful surgical procedure. The avulsion of the labroligamentous complex from the anteroinferior aspect of the glenoid is termed a Bankart lesion (or a bony Bankart lesion if it is accompanied by a fracture). A Bankart lesion is the most common lesion in anterior instability. The tear is usually large enough to involve not only the labrum, where the anterior band of the IGHL inserts, but also the middle labrum and, sometimes, the superoanterior labrum. Tears of the anteroinferior labrum are the most common subtype. The second most common subtype involves tears of the entire anterior labrum. The following classification system was devised to aid in surgical planning:
Computed tomography (CT) arthrography and magnetic resonance imaging (MRI) can help in classifying the lesions for surgical planning. In a Bankart lesion, the scapular periosteum ruptures as the labroligamentous ligaments are avulsed from the glenoid. In Bankart variants, the scapular periosteum remains intact relative to the labroligamentous complex. If the labroligamentous complex is displaced medially and shifted inferiorly, rolling up on itself, the lesion is called an ALPSA lesion. An ALPSA lesion is associated with more severe injury. The diagnosis of this lesion in the acute setting is usually a straightforward procedure employing arthrographic findings. In chronic cases, healing and resynovialization occurs. Therefore, the ALPSA lesion may be difficult for surgeons to visualize during arthroscopy. Avulsion of the inferior glenohumeral joint from its attachment at the anatomic neck of the humerus is known as an HAGL lesion. It is often associated with tears of the subscapularis tendon and results from a shoulder dislocation. A bony humeral avulsion of the glenohumeral ligament (BHAGL) can be similar to an HAGL lesion, but it also involves the bone. This lesion occurs significantly less frequently than classic Bankart lesions. HAGL lesions are seen in approximately 9% of anterior shoulder instabilities. HAGL lesions are treated with surgical reattachment of the GHL to its humeral avulsion site. The IGHL complex may also tear at its midportion. The IGHL complex should be examined along its entire course, from its humeral origin to its labral insertion, since defects have been found at the humeral origin and within the substance of the ligament. If the labroligamentous avulsion occurs with an intact scapular periosteum and if the periosteum is stripped medially, becoming redundant, the lesion is called a Perthes lesion. A Perthes lesion is distinguished from an ALPSA lesion via the redundant periosteum versus the rolled-up, medially displaced periosteal labroligamentous mass. The avulsed labrum resumes a normal position at the glenoid margin, in which partial healing takes place. A GLAD lesion is a tear of the anteroinferior labrum (nondisplaced) with avulsion of the adjacent glenoid cartilage. A glenoid chondral defect is therefore visualized. The labrum is not detached, and there is no capsular stripping. This lesion is clinically stable. The mechanism is glenohumeral impaction in the ABER position. Clinically, these patients complain of pain rather than instability. The lesion can be treated with arthroscopic debridement without need for a stabilization procedure. A Bennett lesion is an extra-articular, posterior, capsular avulsive injury associated with a posterior labral injury and posterior undersurface rotator cuff damage. This injury is seen most commonly in baseball pitchers. The diagnosis of this lesion should raise suspicion for associated labral and rotator cuff abnormalities. The mechanism is from traction of the posterior band of the IGHL during the decelerating phase of pitching. Clinically, the throwing athlete presents with posterior shoulder pain during pitching, with posterior point tenderness. If left untreated, patients progress from functional to anatomic instability. Regarding osseous lesions, infractions or fractures of the glenoid rim (osseous Bankart lesions) are diagnostic of anterior instability when they are demonstrated on radiographs. When these lesions are detected, no other imaging is needed. However, not all anterior instabilities or recurrent dislocations are associated with an osseous Bankart lesion. The sole presence of a Hill-Sachs lesion is pathognomonic of anterior instability and is seen in 50% of patients. The need to detect the lesion is reduced if other pathognomonic findings exist (ie, anterior instability found on physical examination or Bankart lesion). The Hill-Sachs lesion describes a characteristic defect of the posterolateral surface of the humeral head and represents a compression fracture. The resultant lesion is influenced by the patient's age at dislocation and the length of time since the initial dislocation. This is demonstrated as follows:
Intra-articular loose bodies are not uncommon and require surgical intervention. Most loose bodies are composed of bone, cartilage, or both. They may also consist of fibrous tissue, fibrin, fat, or blood. Posterior dislocation Posterior dislocations and posterior glenohumeral joint instabilities are rare (approximately 2-4%). They may result from a fall on an outstretched hand, direct trauma to the shoulder, or violent muscle contractions from electric shocks or seizures. As a result of acute dislocation, instability may occur, and surgical correction of the underlying damage may be indicated. Posterior instability caused by repeated microtrauma without frank dislocations may result in persistent shoulder pain in young athletes. Abduction, flexion, and internal rotation (eg, swimming, throwing, punching) are the mechanisms involved in these cases. When injuries occur in this position, the capsulolabral structures are taut, and the patterns of injury that occur most often are the reverse of those of anterior dislocation. Most patients with atraumatic posterior instability can be treated with conservative measures involving strengthening of the posterior stabilizing muscles. If this fails, surgery may be required. A fall on an outstretched hand with the arm in abduction is another mechanism of posterior dislocation. Posterior instability may also occur as an operative complication in patients with multidirectional instability after a misdirected anterior capsular procedure. An acute posterior dislocation may remain unrecognized in 50% of patients and subsequently may present as a frozen shoulder. The posterior band of the IGHL complex is primarily responsible for capsuloligamentous restraint to a posterior translation of 90° of abduction. The anterosuperior capsule, or rotator interval capsule, also has been shown to be important in limiting the posterior and inferior translation. Imaging findings of posterior dislocation, which typically are the reverse of those found in anterior instability, are as follows:
The most common finding is a tear or shredding of the posterior labrum. The most likely explanation for a high incidence of teres minor tears is that the underbelly of the teres minor muscle is inseparable from the posterior capsule of the GHL. Multidirectional instability Imaging is usually not necessary because this entity is mostly a diagnosis of exclusion. MRI is used principally to exclude conventional causes of instability (ie, Bankart lesion). The patient is usually a young female with bilateral joint laxity. No visible labroligamentous lesions are seen in patients with true multidirectional instability. The capsular mechanism is redundant, and the labrum is often hypoplastic. Degenerative changes of the glenohumeral joint in association with labral degeneration or tearing may be seen. Physical examination with traction applied on a patient's abducted arm causes inferior subluxation of the humeral head. This results in a visible sulcus (sulcus sign) between the prominence of the acromion and the inferiorly subluxed humeral head. Luxatio erecta Luxatio erecta (or inferior dislocation) is uncommon. This dislocation usually occurs when a direct axial force is applied to a fully abducted arm or when a hyperabduction force leads to leverage of the humeral head across the acromion, resulting in inferior dislocation of the humerus. In luxatio erecta, the inferior capsule almost always is torn. Associated bony injuries include fractures of the greater tuberosity, acromion, clavicle, coracoid process, and glenoid rim. Brachial plexus and axillary artery injuries are possible serious complications. Long-term complications include adhesive capsulitis and recurrent subluxations or dislocations. FrequencyInternationalIncidence of traumatic dislocations is as follows:
Mortality/MorbidityShoulder instability has a significant impact on young patients, especially on professional athletes. Evidence suggests that primary repair at the time of injury prevents recurrence. RaceNo preponderance exists in any race. SexNo preponderance exists in either sex. AgeInitial dislocations have been recognized as occurring at 2 age peaks: at 10-30 years and at 50-70 years. AnatomyThe shoulder joint is a synovial joint of the ball-and-socket variety. The bones involved are the hemispherical head of the humerus and the shallow glenoid cavity of the scapula. A 4:1 disproportion exists in the articulating surface areas of the humeral head and the glenoid cavity. This arrangement permits considerable movement. The joint is protected above by an arch formed by the coracoid process, the acromion, and the coracoacromial ligament. The articular cartilage covering the head of the humerus is thicker at the center than at the periphery. The reverse is true in the case of the articular cartilage of the glenoid cavity, with thicker articular cartilage at the periphery than at the center. The soft-tissue supporting structures of the shoulder include the following:
The synovial membrane is reflected from the margin of the glenoid cavity over the labrum and then reflected over the inner surface of the capsule, covering the lower part and sides of the anatomic neck of the humerus as far as the articular cartilage on the humeral head. The tendon of the long head of the biceps brachii passes through the capsule and is enclosed in a tubular sheath of synovial membrane. This membrane is reflected on the long head of the biceps brachii from the summit of the glenoid cavity and is continued around the tendon into the intertubercular groove distally as far as the surgical neck of the humerus. The tendon thus traverses the articulation, but it is not contained within the synovial cavity. Bursae in the neighborhood of the shoulder joint include the following:
The muscles related to the joint include the following:
The arteries supplying the joint are articular branches of the anterior and posterior humeral circumflex and transverse scapular arteries. The nerves are derived from the axillary and suprascapular nerves. Shoulder stability is maintained by articulator and periarticular tissues that collectively are termed the capsular mechanism. The combination of the glenoid labrum and the superior, middle, and inferior GHLs are called the labroligamentous (or capsulolabral) complex. Clinical DetailsAnterior dislocationTypically, a patient with a single dislocation has a history of acute trauma. A patient may describe a feeling of the shoulder popping out. On physical examination, the dislocated shoulder demonstrates a characteristic prominent humeral head anteriorly and a hollow below the acromion. Associated damage to the axillary nerve may occur, with loss of sensation on the lateral aspect of the shoulder, producing the sergeant's-stripe pattern of sensory loss. In the clinical definition of instability, the humeral head slips out of the glenoid socket during activity, causing symptoms. Varying degrees of instability are recognized, ranging from subluxations to dislocations. Anterior instability In posttraumatic instability, the patient usually reports a specific incident, and the shoulder has not returned to its normal position. In many posttraumatic types, a true dislocation has never occurred, and the symptoms are related to recurrent subluxations. The atraumatic type is common in people who play sports, especially those engaging in overhead activities, such as baseball pitchers, javelin throwers, swimmers, and tennis players. The anterior capsule becomes stretched, leading to development of instability. The athlete may present with shoulder pain, an initial episode of subluxation, or episodes of dead-arm syndrome. In dead-arm syndrome, or pain-induced subjective paresis, a patient may experience sharp pain when the shoulder is placed in external rotation or when a force is delivered to the shoulder (as when throwing a hard ball). The patient may then lose control of the arm and even drop an object in hand. After the acute episode, the shoulder may remain sore. The shoulder pain in chronic anterior instability is a result of impingement of rotator cuff tendons due to narrowing of the subacromial space during recurrent anterior translation of the humeral head. This is aggravated by eventual weakening of the rotator cuff muscles, which in turn may lead to failure of humeral depression. Failure of humeral depression in this instance is probably due to imbalance between the deltoid muscle and humeral head stabilizers (rotator cuff muscles). Each deltoid contraction then moves the humeral head superiorly and narrows the space through which the supraspinatus tendon passes. The resultant impingement results in rotator cuff tendinitis. Multidirectional instability Multidirectional instability is usually of the atraumatic type and is often associated with generalized ligamentous laxity throughout the whole body. Multidirectional instability of the glenohumeral joint involves a combination of 2 or 3 instabilities—namely, anterior, posterior, and/or inferior instabilities. Clinically, inferior instability is diagnosed by eliciting the sulcus sign. This is tested with inferior traction on the arm as it is held straight by the side. A positive test result is when the humeral head translates inferiorly so that a visible sulcus is seen between the acromion and the humeral head. Treatment of multidirectional instability involves strengthening exercises of the shoulder stabilizers. Stretching the muscles around the shoulder joint should be avoided. If conservative treatment fails, surgical treatment can be attempted. However, surgical results in patients with generalized ligamentous laxity have been disappointing. Posterior dislocationAcute, traumatic posterior dislocation is far less common than anterior dislocation. Posterior dislocation results from direct trauma to the shoulder or a fall on an outstretched arm in some degree of internal rotation or adduction. Posterior dislocation may also be caused by an electric shock or epileptic seizure. On examination, the patient's shoulder may reveal loss of the normal rounded appearance anteriorly. The shoulder is held in internal rotation and adduction. Limitation of external rotation is marked. Treatment consists of shoulder reduction by applying traction and forward pressure on the humerus. The most common type of posterior instability seen in athletes is the atraumatic type that is part of a multidirectional instability. The shoulder may be voluntarily posteriorly subluxed. Luxatio erectaLuxatio erecta is an uncommon condition. It usually occurs when a direct axial force is applied to a fully abducted arm or when a hyperabduction force leads to leverage of the humeral head across the acromion, resulting in inferior dislocation of the humerus. The patient usually has the arm in a fixed elevated position over the head because the humeral head is immobilized below the inferior aspect of the glenoid. Treatment is reduction (usually under general anesthesia) and evaluation of associated injuries. Preferred ExaminationIn general, the modality chosen depends on its availability and the treatment plan for a particular patient. Radiography is inexpensive and is readily available. It should be performed as the initial imaging investigation in patients presenting with a clinical problem related to the shoulder. It complements the other advanced techniques and provides an overview of the bony components of the shoulder joint. In some patients, radiography obviates further imaging. MR arthrography is the imaging modality of choice to evaluate the labrum. It has the highest sensitivity and specificity of all available modalities. However, it is invasive and may not be necessary in patients in whom surgery is not being considered as a treatment option. Conventional MRI provides a good overview of shoulder lesions and anatomy, particularly the soft-tissue structures. However, it is less accurate than MR arthrography for depiction of small labroligamentous lesions associated with shoulder dislocation. CT arthrography largely has been superseded by MR arthrography. CT arthrography usually is used when MRI is not available. It is useful in showing bony lesions and anterior and posterior labral and capsular lesions. Limitations of TechniquesRadiography cannot demonstrate labral, ligamentous, or capsular lesions. MRI is more sensitive and specific and has superseded CT arthroscopy for demonstrating intra-articular and periarticular soft-tissue structures. Although conventional MRI and MR arthrography are the modalities of choice, their use is limited by their cost and limited availability. In regions with fewer resources, CT arthrography is a good alternative. Limitations of arthrography include discomfort to patients, risk of septic arthritis, and the need for contrast administration. Use of gadopentetate dimeglumine in intra-articular injections has not been approved by the Food and Drug Administration (FDA). DIFFERENTIALSSection 3 of 9
Shoulder, Glenoid Labrum Injury (MRI) Shoulder, Rotator Cuff Injury (MRI) Shoulder, Rotator Cuff Injury (Ultrasonography) Other Problems to Be ConsideredImpingement and biceps subluxation may occasionally accompany glenohumeral joint instability. Rotator cuff disease, superior labral anteroposterior (SLAP) lesions, and glenoid labrum cyst have been associated with glenohumeral instability. Rotator cuff tears are found in more than 25% of patients with shoulder dislocations. Ganglion cysts often are associated with instability. In particular, a strong association exists with superior labrum tears; however, these cysts can arise from virtually all aspects of the glenohumeral joint. RADIOGRAPHSection 4 of 9
FindingsAnterior shoulder dislocation and instability Radiographs are used to diagnose dislocations of the shoulder (see Image 1) and can depict the following:
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
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 ConfidenceTo 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. CT SCANSection 5 of 9
FindingsThe 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). 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
Posterior instability
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. False Positives/NegativesMost 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. MRISection 6 of 9
FindingsMRI findings can be divided into those demonstrated on conventional MRIs and those demonstrated on MR arthrograms. Conventional MRIAnterior instability
A classification system for abnormal labral intensity has been formulated for conventional MRI as follows:
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. As of late December 2006, the Food and Drug Administration had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. 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 thewhites 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 arthrographyThe 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
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 ConfidenceConventional 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/NegativesCommon 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:
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. INTERVENTIONSection 7 of 9
Medical/Legal Pitfalls
MULTIMEDIASection 8 of 9
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