Reviews and Commentary n Review 323 ------

1 www.rsna.org/rsnarights. nstability I nterior nterior A RSNA, 2013

dislocation, chronic instability with repeated dislocation, repeated with instability chronic dislocation, dislocation. The instability without repeated and chronic of the pathophysiology dislocation and biomechanics of dis discussed. The authors injury are labral-ligamentous the acutely trauma in occur that findings the tinguish unstable those that typify the chronic tized from also imaging modalities are of different . The roles arthrography distinguished, including magnetic resonance The goal of specialized imaging positions. and the value Image inter of imaging depends on the clinical scenario. need to emphasize diagnosis may reporting and pretation associated with are and the identification of lesions that of lesions for treatment instability or the characterization planning. q In the shoulder, the advantages of range of motion are of motion are of range the advantages In the shoulder, to injury of vulnerability for the disadvantages traded insta Glenohumeral of instability. and the development spectrum of clinical com a broad bility encompasses can be obvious The diagnosis plaints and presentations. unsuspected. Imaging findings depend on nu or entirely osseous defects to gross from and range factors merous and undetectable capsular abnormalities labral equivocal focuses on the imaging findings in review This lesions. shoulder clinical scenarios: acute first-time distinct three

maging maging in Glenohumeral Glenohumeral I radiology.rsna.org

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[email protected] Volume 269: Number 2—November 2013 269: Volume repeated dislocation diagnosis of anterior glenohumeral instability Evaluate the MR imaging findings that can help radiologists distinguish acute first-time shoulder dislocation from chronic instability with or without Describe the biomechanics of dislocation and the pathophysiology of labral-ligamentous injury Describe the roles of different imaging modalities in the See www.rsna.org/education/ry_cme.html Online CME J.T.B. (e-mail: (e-mail: J.T.B.

RSNA, RSNA, 2013

From the Department of Radiology, NYU Hospital for the Department of Radiology, From

provider of CME, obtain signed disclosure statements from the authors, editors, and reviewers for this activity. For this journal-based CME activity, author disclosures are listed at the end of this article. activity. Statement Disclosure The ACCME requires that the RSNA, as an accredited commensurate with the extent of their participation in the medical education for physicians. The RSNA designates this medical education for physicians. journal-based CME activity for a maximum of 1.0 Category 1 Credit Accreditation and Designation Statement Accreditation Council for The RSNA is accredited by the Continuing Medical Education (ACCME) to provide continuing n After reading the article and taking the test, the reader will the test, and taking After reading the article be able to: n n Learning Objectives: q October 4, 2012; revision requested November 5; revision October 4, 14; final 2013; accepted February received January 27, 26. version accepted February to for Musculoskeletal Care, NYU School of Medicine, 301 E NYU School of Medicine, for Musculoskeletal Care, S.G.); and NY 10003 (J.T.B., York, New Sixth Floor, 17th St, Massachusetts General Hospital, Department of Radiology, Received Mass (W.E.P.). Boston, Harvard Medical School, 1 NYU Center NYU Langone Medical Center, Joint Diseases, Radiology: William E. Palmer, MD Palmer, William E. Jenny T. Bencardino, MD Bencardino, T. Jenny MD Soterios Gyftopoulos, REVIEW: Imaging in Anterior Glenohumeral Instability Bencardino et al

he glenohumeral joint has the Glenohumeral instability can be- Biomechanics greatest range of motion of any come the immediate sequelae of trau- Tmajor articulation in the human matic injury or evolve gradually owing to Dynamic and passive restraints to- body. The trade-off for this mobil- cumulative stresses related to occupa- gether provide glenohumeral stability, ity is vulnerability to injury and the tional or sport-specific activities (2). De- maintaining nearly perfect rotation of development of shoulder instability. pending on the clinical scenario and the the humeral head over the center of Dynamic stabilizers of the joint, in- needs of the treating physician, imaging the . Dynamic stabilizers cluding the cuff muscles, are insuf- has different roles. In the acute setting include the rotator cuff and long head ficient to maintain normal glenohu- following first-time shoulder dislocation, of biceps as well as pectoralis major, meral location and function (1). Joint MR imaging is used to characterize the latissimus dorsi, and periscapular mus- stability also depends on the passive location and extent of structural dam- cles (1). Passive stabilizers include constraints provided by intact static age and typically demonstrates an obvi- the glenoid rim and concave glenoid structures, especially the glenoid rim, ous, pathognomonic pattern of osseous fossa, labrum, and capsuloligamentous glenoid labrum, and glenohumeral lig- edema, hemarthrosis, and labrocapsu- structures (1). The congruent articu- aments. The vast majority of unstable lar injury. But as dramatic as these MR lar surfaces provide stability through demonstrate characteristic findings can be, they may not predict the principle of concavity compression, abnormalities of the labral-ligamen- repeated dislocation or the future devel- which is particularly important during tous complex on magnetic resonance opment of glenohumeral instability (3). the midrange of glenohumeral move- (MR) images (2). In the setting of repeated dislocations, ment when the capsular are when the clinical diagnosis of instabil- lax (4). The surrounding muscles cre- ity becomes unambiguous, MR imag- ate this dynamic joint compression and Essentials ing may be able to show osseous and primary stabilization during the mid- nn Trauma accounts for more than soft-tissue abnormalities that can guide range (5). At the extremes of motion, 90% of first-time anterior shoul- surgical planning and the choice of sta- the glenohumeral ligaments contribute der dislocations. bilization procedure. most to stability, especially the inferior nn Reciprocating humeral and gle- Shoulder instability also occurs in labral-ligamentous complex (5). noid lesions are pathognomonic individuals who deny previous disloca- The glenohumeral ligaments (supe- for articular malalignment (dislo- tions and major traumatic events (2). rior, middle, and inferior) are formed cation) at the time of trauma and In one subset of these patients, func- by discrete capsular bands that attach are strongly associated with in- tional disability and positive provocative to the labrum and adjacent glenoid rim juries to stabilizing soft-tissue testing lead to confident clinical conclu- (5–9). The superior and middle gleno- structures. sions. In another subset, equivocal his- humeral ligaments arise anterosuperi- nn There are two major causes at tory and physical examination lead to orly, just anterior to the biceps tendon. either end of a continuum; at challenges in diagnosis (2). If imaging The superior glenohumeral one end of the spectrum, a is requested, the history may state a merges with the coracohumeral liga- major traumatic event causes question about the presence of rotator ment in the rotator interval and pass- first-time dislocation followed by cuff tear or biceps lesion, possibly mis- es between the supraspinatus and the repeated dislocations requiring leading the radiologist interpreting the subscapularis to the lesser tuberosity lesser degrees of force and imaging study (2). at the bicipital groove. Together with provocation. In this review, we focus on imag- the coracohumeral ligament, the supe- ing findings in three distinct clinical rior glenohumeral ligament functions as nn At the other end of the spec- scenarios. The first scenario involves a primary passive restraint to inferior trum, there is no antecedent acute first-time shoulder dislocation. trauma; glenohumeral hypermo- The second applies to chronic insta- bility, which may be developmen- bility with repeated dislocation. In the Published online 10.1148/radiol.13121926 Content code: tal, leads to multidirectional in- third scenario, there is chronic insta- stability that worsens over bility without repeated dislocation. We Radiology 2013; 269:323–337 months and years. distinguish imaging findings that char- Abbreviations: nn In the latter scenario, instability acterize the acute setting from those ABER = abduction-external rotation causes symptoms due to recur- that characterize the chronic unstable ALPSA = anterior labral-ligamentous periosteal sleeve rent glenohumeral subluxation, joint. We also distinguish the roles of avulsion not dislocation; because the different imaging modalities, including GLAD = glenolabral articular disruption degree of subluxation may be conventional MR imaging versus MR HAGL = humeral avulsion of the glenohumeral ligament IGL = inferior glenohumeral ligament minimal, this condition has also arthrography, and the value of special- 3D = three-dimensional been described clinically as rela- ized imaging positions such as abduc- tive instability. tion-external rotation (ABER). Conflicts of interest are listed at the end of this article.

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Figure 1

Figure 1: 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-sup- pressed 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 . No glenoid rim fracture is present. translation of the adducted shoulder attached to a torn labrum or is stripped Adduction-external rotation has been (10). The middle glenohumeral lig- medially along the glenoid neck with advocated for postreduction immobili- ament courses inferiorly toward the its periosteal sleeve, the IGL becomes zation as a way to displace joint fluid lesser tuberosity and blends into the incompetent and the shoulder becomes posteriorly and approximate the de- capsular sheath of the subscapularis unstable (10,12). The IGL is best vi- tached labrum to the anterior glenoid tendon. The middle glenohumeral liga- sualized on arthrographic MR images, rim and promote healing (16,17). Post- ment shows the greatest developmental with or without ABER positioning, and reduction images are used to charac- variation, but differences in morphol- on conventional MR images when an terize residual alignment abnormalities ogy do not seem to affect glenohumeral effusion is present (13,14). Because the and fractures. If reduction is not pos- stability (11). The middle glenohumeral IGL is a constant anatomic structure, sible, cross-sectional imaging may be ligament limits anterior translation its labral attachment site can be pre- necessary in the acute setting to guide when the shoulder is externally rotated sumed with confidence even though the additional manipulation or surgery on and moderately abducted (10). Both lack of effusion prevents visualization. the basis of the presence of osseous the superior and middle glenohumeral A labral tear located at this presumed (engaging Hill-Sachs defect, obstructing ligaments are commonly depicted on attachment site is closely associated fracture fragment from the glenoid or conventional and arthrographic MR with glenohumeral instability (15). humeral head) or soft-tissue (intraar- images. ticular biceps dislocation blocking re- The inferior glenohumeral ligament alignment) lesions (18). (IGL) is composed of an anterior band, Imaging Modalities and Techniques Arthrographic MR imaging has lit- a posterior band, and the intervening In most circumstances, radiographs are tle or no role in the acute setting when axillary pouch. Compared with the first obtained following acute shoulder conventional MR images demonstrate superior and middle glenohumeral lig- dislocation. Prior to reduction, radio- periarticular edema or hemorrhage, aments, the anterior band of the IGL graphs demonstrate the direction of depict the location and severity of bone is critical to passive joint stabilization humeral translation. The usual trauma marrow injuries, and elucidate the trau- (12). It typically courses from the an- series can include anteroposterior in- matic mechanism. Effusion, or hemar- teroinferior labrum, where it forms ternal rotation, anteroposterior exter- throsis, provides an arthrographic effect a sleeve of continuous tissue with the nal rotation, scapular “Y” and axillary in 97% of cases (19) by distending the glenoid rim, capsule, and periosteum, views, assuming the patient can tol- joint capsule and outlining intraarticular to the humeral metaphysis. The IGL erate positioning. Additional Stryker structures, including the labrum, the gle- becomes taut in the ABER position, notch and West Point views help to con- nohumeral ligaments, articular cartilage, resisting anteroinferior glenohumer- firm the presence of Hill-Sachs lesion and intraarticular loose bodies (Fig 1). al translation (10). When the IGL is or Bankart fracture, respectively (2). MR imaging has the added benefit of

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Figure 2 of the glenoid and require nonstandard sequences to depict the osseous injuries of the glenoid and hu- meral head and can be incorporated into the conventional MR imaging pro- tocol with minimal added imaging and postprocessing time (30).

Clinical Scenarios

Acute First-Time Shoulder Dislocation The prevalence of anterior shoulder dislocation is reported to be as high as 2% in the general population (31–33). Although the location and severity of structural damage directly influence the Figure 2: Acute first-time anterior shoulder dislocation: T1-weighted MR images in a 26-year-old man likelihood of repeat dislocation, patient with shoulder pain after a single anterior dislocation. MR arthrography was performed 2 months after known age at presentation is another impor- dislocation owing to persistent pain and limitation. A, Axial fat-suppressed image demonstrates an intact tant factor determining recurrence rate anterior labrum (arrow). B, ABER image demonstrates an avulsion of the anterior labrum with an intact (34,35). The rate of recurrent disloca- glenoid periosteum and capsule (arrow), highlighting the mechanical advantage of having the shoulder in this tion is inversely related to age. Rowe position during imaging. (35) found that only 16% of patients demonstrating abnormalities of the ro- (Fig 2). In a series of 256 patients, older than 40 years at the time of first tator cuff and biceps tendon. ABER images improved the diagnostic dislocation will have dislocation again, Once the acute situation has performance of MR arthrography from compared with 83% of patients younger passed, MR arthrography becomes an 48% to 89% sensitivity (21). Used alone than 20 years. In young athletes who option, assuming that fluoroscopy or to evaluate the anteroinferior labral- return to sports activities and competi- sonography is available to guide needle ligamentous complex, ABER images tion, the likelihood of repeat dislocation placement for the intraarticular injec- demonstrated the same accuracy as the further increases to 92% (34). Even in tion of contrast material. Some refer- full complement of arthrographic MR athletes, the recurrence rate drops to ring physicians are satisfied with con- sequences (23). FADIR may improve 50%–75% between 20 and 25 years of ventional MR, whereas others prefer assessment of the posterior labrum and age (36). Repeated dislocation has been arthrographic MR and the diagnostic capsule (24), whereas ADIR may have reported to occur three times more fre- confidence provided by intraarticular advantages to ABER in discriminating quently in young men compared with contrast material. MR arthrography between different Bankart subtypes women (36). Noncompetitive activity has the most compelling role in the as- (25). level may also play a role, as shoulder sessment of younger individuals with In the setting of repeated disloca- dislocation has been reported more suspected instability, when subtle tions and known instability, some re- commonly in military personnel com- labral-ligamentous abnormalities have ferring physicians prefer computed to- pared with the general population (37). profound influences on shoulder func- mography (CT) or CT arthrography for Whereas nonsurgical management is tion, management, and prognosis (20). characterizing the sizes and locations of the usual treatment in older patients, Provocative positioning maneuvers, osseous defects and for guiding preop- stabilization surgery may be necessary including imaging in both internal and erative planning. CT reformations and to avoid recurrent dislocation and in- external rotation, ABER, flexion-ad- three-dimensional (3D) reconstructions stability in younger athletes unwilling to duction and internal rotation (FADIR), lend themselves to quantitative analysis modify their activities or follow rehabil- and adduction-internal rotation (ADIR), (26–29). Although CT has a proved itation programs (34,37). have been proposed to improve visuali- track record in the segmentation of Trauma accounts for more than zation of the labral-ligamentous complex cortical bone, 3D reconstruction, and 90% of first-time anterior shoulder dis- (14,21). Although ABER positioning was quantification of osseous defects, MR locations (31–36). A common traumatic initially described as increasing sensi- imaging techniques can be modified to mechanism is fall on an outstretched tivity in the diagnosis of articular-sided provide similar information. In patients hand, or FOOSH. In contact sports, rotator cuff lesions (22), it is now rec- with glenoid rim deficiency, CT and MR dislocation also results from forced ognized as improving the detection of have been shown to generate compa- ABER or a direct posterior blow to the nondisplaced anteroinferior labral tears rable quantitative measurements (22). shoulder (38). In individuals with devel- at the attachment site of the IGL (20,21) Three-dimensional MR reconstructions opmental glenohumeral laxity, inherent

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instability predisposes the shoulder to Figure 3 traumatic dislocation with lesser de- grees of force (35). Owens et al (39) distinguished dislocation from subluxa- tion depending on whether the shoulder required manual reduction maneuver at the time of injury. In their population of military cadets, nearly all of the sub- luxated shoulders, despite spontaneous reduction, demonstrated both Bankart and Hill-Sachs lesions on the basis of MR and arthroscopic images. The au- thors concluded that initial, traumatic subluxation produced the same patho- logic lesions as dislocation and warrant- ed the same cautionary prognosis and management. Therefore, patients with traumatic transient subluxation should be considered for early surgical stabi- lization to enable the anatomic repair of a detached labrum and reduce the Figure 3: MR images of acute ALPSA in a 24-year-old man who sustained a first episode of anterior risks of worsened intraarticular dam- shoulder dislocation 3 weeks prior to imaging. A, Fat-suppressed T2-weighted and, B, axial fat-suppressed age, chronic instability, and recurrent intermediate-weighted images demonstrate a Hill-Sachs lesion (white arrow) with marrow edema and subluxation or dislocation (39). associated anteroinferior labral tear with anteromedially displaced fragment (open arrow). Note stripping and Osseous injury.—At the time of edema of the scapular periosteum with developing granulation tissue (black arrow). dislocation or subluxation, as the hu- meral head slides over the glenoid support the diagnosis of glenohumeral line. In the acute setting, when bone rim and relocates in the glenoid cav- dislocation. As the osseous contusion marrow edema is present, the fracture ity, shear forces and osteochondral heals over weeks or months, the edema line is better characterized on T2- compression can produce reciprocating dissipates and, along with it, valuable weighted compared with T1-weighted osseous lesions of the posterosuperior biomechanical information (42). There- MR images (42). CT reformations in humeral head and anteroinferior gle- fore, marrow contusion only provides the oblique sagittal plane show nondis- noid (1) (Fig 3). Compared with the biomechanical information if MR im- placed fracture lines and small corti- hard, wedge-shaped cortex of the an- aging is performed relatively soon after cally based fragments. Three-dimen- terior glenoid rim, the flat contour and traumatic injury. sional CT reconstructions depict the softer trabecular bone of the humeral Whereas Hill-Sachs defect is location of a displaced fragment and head make it susceptible to Hill-Sachs the more common imaging finding the size of its donor site. fracture. Following first-time anterior following dislocation, glenoid rim Less common osseous injuries in- dislocation, 25%–81% of shoulders fracture has the greater prognostic volve the site of tendon attachments. show Hill-Sachs defects at arthroscopy significance. The risk for recurrent The coracoid process is infrequently (27,40,41). dislocation and chronic instability in- fractured, typically as a result of direct On MR images of the shoulder, the creases with the size of the glenoid impaction by the dislocated humeral appearance of an impaction lesion de- bone defect (43–45). In the acute head (3%–13%) (48). Tuberosity pends on the time interval between im- setting, displaced glenoid fragments fractures occur in 15%–35% of dislo- aging and traumatic injury. In the acute may prohibit relocation, requiring cated shoulders, especially in older pa- and subacute settings, conventional MR surgical reduction and internal fixa- tients who are also susceptible to rota- imaging demonstrates bone marrow tion (46,47). A nondisplaced fracture tor cuff tears (49). Greater tuberosity edema on both T1- and T2-weighted can heal with conservative treatment fractures in the setting of anterior images, although fat-suppressed T2- if repeated injury is avoided through shoulder dislocation may involve the weighted images are more sensitive for activity modification. Unfortunately, attachment sites of supraspinatus and regions of subtle marrow edema (42). nondisplaced fractures can be difficult infraspinatus tendons (50–52). Dis- Proton-density images without fat sup- to identify on MR images. Oblique sag- placed fractures of the greater tuber- pression cannot reliably demonstrate ittal images, when prescribed in the osity may require surgical intervention marrow edema (42). In the absence plane of the glenoid fossa, best dem- if the cuff tendon becomes interposed of Hill-Sachs defect, the location and onstrate the glenoid contour and the between the fragment and its donor pattern of marrow injury can help to presence of an anteroinferior fracture site on the humeral head (18,53–55).

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Figure 4 The inferior labral-ligamentous lesion may be subtle or not apparent complex, the primary passive stabi- on axial images, it may become more lizer of the joint, can demonstrate apparent on ABER images owing to the an abnormality anywhere along its traction provided by the inferior gleno- course from the glenoid rim to the humeral ligament on the labrum (65). humerus. After first-time dislocation, During dislocation, shear forces four injuries of the inferior labral-lig- and osseous impaction can damage the amentous complex have characteristic articular cartilage over the anteroin- appearances on MR images. These ab- ferior glenoid fossa. The GLAD lesion normalities include the , combines a labral tear with an adjacent the Perthes lesion, the glenolabral ar- cartilage defect (66). When the labral ticular disruption (GLAD) lesion, and tear is minimal, patients complain of the humeral avulsion of the glenohu- pain from the osteochondral defect meral ligament (HAGL) lesion (20). rather than instability (67). Whereas At the time of glenohumeral dislo- conventional and arthrographic MR im- Figure 4: Axial fat-suppressed intermediate- cation or subluxation, traction on the ages both show focal cartilage loss and weighted MR image of subacute first-time dislo- IGL is transmitted to the labrum, which full-thickness defects, neither imaging cation in a 32-year-old man with a prior anterior can be torn partially or detached com- examination may be successful in dem- shoulder dislocation 6 weeks prior to imaging. There pletely from the glenoid rim. Avulsion onstrating small, delaminated chondral is a minimally displaced, detached tear of the ante- of the labrum, which requires disrup- flaps (68). Effusion and intraarticular rior labrum (white arrow) with tearing of the adjacent tion of its periosteal sleeve, is called a contrast material administration im- capsule (black arrow), consistent with a Bankart Bankart lesion, the classic pathoana- prove the likelihood of visualizing chon- lesion, and flattening of the anterior glenoid margin, tomic hallmark of anterior instability dral flaps (68). consistent with a mildly impacted fracture. that Bankart described as the “essen- When failure occurs at the humeral tial” lesion in recurrent shoulder dislo- attachment site, it is called a HAGL le- cation (Fig 4) (15). This injury occurs sion (66,69,70) (Figs 5, 6). Bigliani et Although lesser tuberosity fractures at the anteroinferior IGL attachment al (71), in a cadaver study investigat- are exceedingly uncommon in anterior site and represents the most common ing the tensile properties of the inferior shoulder dislocation, the subscapularis labral injury following first-time trau- labral-ligamentous complex and its sites is more susceptible to myotendinous matic dislocation (59). In the acute set- of mechanical weakness, reported that or contusion compared with su- ting when effusion is present, conven- the labrum failed 40% of the time, the praspinatus and infraspinatus (56,57). tional MR images show fluid separating IGL substance failed 35% of the time, Subscapularis injuries may have prog- the labrum from the glenoid rim. and the humeral insertion failed 25% nostic implications in older patients The Perthes lesion, first described of the time. In the clinical literature, owing to its role in static and dynamic in 1905, is similar to the Bankart lesion the incidence of HAGL is substantially stabilization of the glenohumeral joint in that the labrum is separated from lower than the 25% predicted by the (58). In high-grade subscapularis tear, underlying articular cartilage but dif- biomechanical research of Bigliani et al chronic instability is more likely to de- fers in that the labrum remains partially (71). The discrepancy reflects, in part, velop and a Bankart repair is less likely attached to the glenoid rim by an in- the differences between cadavers in to succeed. tact periosteal sleeve (60,61). Because the laboratory versus athletes on the Soft-tissue injury.—During the days the periosteum is weak, the IGL loses playing field but also is demonstrative and weeks following shoulder disloca- function and the shoulder becomes un- of the difficulty in diagnosing HAGL le- tion, MR imaging findings typically in- stable. Whereas the Bankart lesion is sions. At arthroscopy or open surgery, clude effusion and periarticular edema most closely associated with traumatic the HAGL lesion can be missed unless or hemorrhage. When hemarthrosis is dislocation, the Perthes lesion can re- a targeted search is triggered by the present, the joint fluid is increased in sult from either dislocation or cumula- knowledge gained from preoperative signal intensity compared with muscle tive stresses on the IGL owing to physi- imaging (12,63,69,70,72,73). on T1-weighted images (19). Intraar- cal overuse and repetitive microtrauma In the acute setting, IGL injury is ticular fluid creates an arthrographic (62,63). The Perthes lesion is more associated with periarticular edema effect, outlining structures, filling de- difficult to diagnose on MR images and hemorrhage that localize to the fects, and improving diagnostic confi- since the torn labrum can be normal axillary pouch, quadrilateral space, and dence. Localized extraarticular edema or nearly normal in anatomic position. proximal humerus at the base of the or hemorrhage can also provide diag- Therefore, it can be overlooked not lesser tuberosity on MR images (74). nostic advantages by calling attention only on MR images but also at surgery Although the degree of IGL injury can to a region of capsular or myotendi- unless the arthroscopist probes the la- be overestimated if hemorrhage is ex- nous injury. brum carefully (64). While the Perthes tensive (75), it should trigger a directed

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Figure 5

Figure 5: 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 reconstruc- tion 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). search for additional findings that sup- stump of the anterior band of the IGL MR imaging performed 21–54 days port a more specific diagnosis of HAGL (76,77). Following primary traumatic later (74). Findings specific for HAGL lesion. The “J” sign (in a right shoulder; shoulder dislocation, IGL abnormalities lesions were identified in 21% of these reversed “J” in a left shoulder) is fairly were identified in 52% of shoulders at shoulders at baseline but only 7.1% specific for IGL rupture and occurs on baseline MR imaging performed within at follow-up. These results reinforce oblique coronal images when edema and 7 days of trauma compared with 12% the difficulty in diagnosing HAGL le- hemorrhage outline the torn, retracted of the same shoulders at arthrographic sions on MR images, especially months

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Figure 6 In contrast to the osseous lesions and during dislocation and the magnitude labral-ligamentous tears that charac- of compressive force (83). terize trauma-related instability, lax Hill-Sachs defects rarely require shoulders may show minimal MR im- surgical treatment unless they are large aging findings (79). Despite repeated enough to cause mechanical symptoms dislocations, the labrum can be normal or engage the glenoid rim (83–89). in appearance or blunted and mildly de- Larger lesions of the humeral head may ficient (59,63). On the basis of MR find- be associated with catching, clicking, or ings alone, therefore, the evidence for popping (90). The engaging Hill-Sachs instability may be minimal or equivocal. defect extends into the articulating sur- Glenohumeral instability is the ob- face of the humeral head. In the ab- vious clinical diagnosis when recurrent ducted and externally rotated position, dislocations follow initial traumatic the glenoid rim drops into this defect dislocation. In this setting, the role of causing apprehension and subluxation imaging shifts from lesion detection to in mild cases or locking and dislocation lesion characterization for treatment in severe cases (91). When conserva- Figure 6: Chronic multidirectional instability in a planning. MR or CT imaging is typi- tive treatment fails, surgical options 41-year-old woman with apprehension, disability, cally requested to guide the surgical include remplissage, bone grafting, and provocative testing positive for instability and approach and the choice of stabilization osteoarticular allograft reconstruction, without previous dislocation or major traumatic procedure. Depending on the presence resurfacing arthroplasty, and hemiar- event. At conventional MR imaging of the shoulder and severity of osseous versus soft tis- throplasty (92). Functional assessment 5 weeks earlier at an outside institution, findings sue lesions, the surgeon may decide based on clinical criteria, not imaging were interpreted as negative for labral-ligamentous on open surgical versus arthroscopic criteria, differentiates the engaging le- injury. On this oblique coronal fat-suppressed T1- visualization (2). The primary goal of sion from the nonengaging lesion (91). weighted arthrographic MR image, contrast material the stabilization procedure may be the MR and CT imaging aid in preoperative outlines the anterior band of the inferior glenohu- reconstruction of humeral and glenoid planning by showing the location and meral ligament (black arrow), which is ruptured and osseous defects or the repair of antero- size of the Hill-Sachs defect, as well as retracted from its humeral attachment site. Contrast inferior capsulolabral soft tissues (2). the percentage of involved articular sur- material leaks from the joint into the quadrilateral Many of the same osseous and face (90,93). space (white arrow). Capsulorrhaphy was performed labral-ligamentous lesions are seen The glenoid rim can become flat- arthroscopically. in first-time and recurrent disloca- tened and deficient due to fracture, tors (80,81). In arthroscopic studies bony remodeling, or a combination of after injury when the damaged tissue comparing these groups, hemarthro- both (94) (Fig 5). If a fracture frag- has healed and remodeled but the IGL sis, HAGL lesion, and other capsular ment resorbs over time, its donor site remains incompetent (74). The prev- injuries were more common in acute is exposed on the glenoid rim. Smaller alence of bony HAGL lesion (avulsion primary dislocation, whereas Bankart glenoid defects cause instability due to of humeral cortex along with the IGL) lesion, anterior labral-ligamentous incompetence of the inferior labral-liga- ranges from 0% to 20% in the litera- periosteal sleeve avulsion (ALPSA) le- mentous complex. With increasing loss ture (74,77). sion, capsular laxity, Hill-Sachs defect, of bone stock, articular incongruency glenoid rim deficiency, and greater tu- creates a mechanical mismatch that Chronic Instability with Repeated berosity fracture were more common predisposes to recurrent dislocation Dislocation in chronic repeated dislocation (80,81). and severe functional disability (83). Traumatic shoulder dislocation can lead Glenoid rim fracture and rotator cuff Image interpretation should take to chronic instability and repeated dis- tear occurred in both groups but were into account the size of the glenoid le- locations requiring successively lesser more frequent in repeat dislocators sion and the contour of the glenoid rim. degrees of force and provocation (78). (80,81). Recurrent dislocation increases in like- This topic will be addressed in the Osseous injury.—The prevalence lihood when the anteroposterior width following paragraphs. Chronic instabil- of Hills-Sachs defects increases from of the glenoid defect measures 21% or ity and repeated dislocations may also 25% in first-time dislocators to 40%– more of the total glenoid length, or the develop without antecedent trauma 90% in repeat dislocators (81,82). The glenoid articular surface area decreases (3). This disorder, which is beyond the defects enlarge in size with increasing by 20%–30% (44,45). Once the glenoid scope of our review, results from ex- numbers of dislocations, eventually defect reaches approximately 25% of cessive laxity and stretching of the gle- taking the signature hatchet morphol- glenoid width, the glenoid changes in nohumeral joint capsule. As hypermo- ogy (83). The location and orienta- appearance from a pear shape to an in- bility worsens over time, the shoulder tion of the impaction fracture depend verted pear shape (44). The amount of develops multidirectional instability. on the position of the humeral head glenoid bone loss guides management.

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When the loss of bone stock is mild Latarjet procedure, in particular, can calculation of glenoid surface area (less than 15% of glenoid width and/or be done either as an open procedure or (95,98,99). CT arthrography improves 10% of glenoid surface area), open arthroscopically (96,97). Classically, it soft-tissue evaluation, but iodinated or arthroscopic soft-tissue repairs are has been used as a secondary method contrast material may limit quantita- usually sufficient (43,95). When mod- of repair for patients who have failed tive osseous assessment because the erate (15%–30% of glenoid width and/ initial surgical stabilization treatment, injected contrast solution can have the or 10%–25% of glenoid surface area), but it is becoming increasing more pop- same attenuation as cortical bone and bone augmentation may be appropri- ular as a first-line treatment option for fracture fragments. Although CT has ate in patients who are physically ac- the patient with recurrent shoulder in- been in use for a longer period of time tive (47). When severe (more than stability (96,97). for the quantification of glenoid defi- 30% of glenoid width and/or 25% of Conventional CT enables two- ciency, MR imaging techniques can be glenoid surface area), surgical treat- dimensional reformations and the modified to provide similar informa- ments prevail, including glenoid re- segmentation of cortical bone for 3D tion (29,30). The MR protocol is more construction with bone graft from the reconstructions. Reformations in the time-intensive due to specialized imag- iliac crest or transfer of the coracoid plane of the glenoid fossa allow stan- ing sequences and postprocessing, but process (Bristow and Latarjet pro- dard quantification techniques, such after further validation MR should be cedures) (47,71,72,95) (Fig 7). The as measurement of defect width and able to duplicate the results of 3D CT

Figure 7

Figure 7: Substantial glenoid bone loss in a 38-year-old woman treated by means of tibial allograft augmentation. A, Sagittal T1-weighted MR, B, sagittal CT reconstruction, and, C, axial CT images demonstrate anterior glenoid bone loss (arrow). D, Axial CT and, E, 3D CT images after glenoid reconstruction using a tibial allograft demonstrate a portion of the coracoid process (arrows) along the anterior margin of the glenoid, parallel to the articular surface.

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Figure 8 arthrographic MR images show a char- acteristic pattern of findings (65,66) (Fig 8). On axial and oblique coronal images, the anteroinferior glenoid rim is deficient, or bare. This absence of labrum is a clue that the labral-liga- mentous complex may be displaced and should lead to a targeted search for fo- cal soft-tissue thickening along the gle- noid neck 5–15 mm medial to the gle- noid rim (65,66). Because the diagnosis of ALPSA lesion is most certain when the IGL can be identified and followed to the thickened periosteal sleeve, ar- thrographic MR, with or without ABER positioning, has diagnostic advantages over conventional MR (65,66). HAGL lesions, and capsular injuries in general, are more likely to be identi- fied when MR imaging immediately fol- lows the traumatic event (74). Because of the healing process and the remod- eling of capsular tissue in the axillary pouch, the IGL can scar down to the humerus and appear normal in con- tour at arthroscopy despite repeated Figure 8: Chronic ALPSA in a young baseball player with clinical findings of anteroinferior dislocations (69). If the IGL does not instability and no history of prior dislocation. A, B, Axial and, C, sagittal fat-suppressed T1- scar down to the humerus, mechanical weighted MR arthrograms demonstrate a medially displaced anteroinferior labral tear (black insufficiency can cause chronic insta- arrows) and stripped off scapular periosteum with scar tissue annealing the fragment and peri- bility (70). The capsular defect at the osteum to the inferomedial scapular neck (white arrows). (Image courtesy of Jason Mayo, MD.) humeral attachment site enables the development of a pseudo-pouch adja- and obviate the exposure to ionizing degenerative changes such as subchon- cent to the normal axillary pouch (74). radiation (29,30). dral sclerosis and bony remodeling This pseudo-pouch may be difficult to Soft-tissue injury.—During the develop at the anteroinferior glenoid identify on conventional MR images months and years following acute first- fossa (100). When acute dislocation unless it becomes distended by effu- time dislocation, labral-ligamentous is superimposed on chronic instability, sion (74). At MR or CT arthrography, lesions evolve depending on numerous hemarthrosis and bone marrow contu- contrast material fills the pseudo-pouch factors, such as the location of initial sion may coexist with the sequelae of and flows distally along the humerus tissue damage, the activity level of the repeated dislocation. into the quadrilateral space near the individual, and the numbers of inter- The ALPSA lesion is common in axillary nerve and inferior circumflex val dislocations (80,81). Some lesions, chronic instability and can arise from neurovascular bundle, giving the ap- such as the Bankart lesion, can be pre- the Perthes lesion (65,101). If the peri- pearance of two axillary pouches (Fig sent following first-time dislocation or osteum remains attached to the la- 6). In the months and years following repeated dislocations. Over time, non- brum, traction is transmitted along the trauma, this pseudo-pouch suggests the displaced Bankart lesions become dis- IGL, stripping the periosteum medially diagnosis of HAGL lesion (74). CT may placed from the glenoid rim (72). As along the glenoid neck. With repeated better demonstrate the bony HAGL, the degree of displacement increases, dislocation or subluxation, the labral- which occurs when IGL avulsion is as- the anteroinferior glenoid rim appears ligamentous complex retracts medially sociated with cortical fracture or peri- bare, or deficient, of labrum (Fig ).8 with the periosteum, rolling up like osteal detachment. GLAD lesions also evolve. With re- a shirtsleeve. It can scar down to the peated dislocations, chondral flaps in- glenoid neck and become immobile Chronic Instability without Repeated crease in size and detach from the gle- (101). Although the healing process Dislocation noid fossa, leading to focal cartilage loss creates a smooth, synovialized surface This scenario poses the greatest diag- and intraarticular loose bodies (100) that can obscure the ALPSA lesion at nostic challenges. In acute first-time (Fig 9). With progressive cartilage loss, arthroscopy, both conventional and dislocation and chronic instability with

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repeated dislocation, the clinical his- Figure 9 tory, signs and symptoms, and imaging findings are usually straightforward. In chronic instability without repeated dis- location, disability results from glenohu- meral subluxation or micro-motion, not dislocation (62,102–105). Because the degree of subluxation may be minimal, this condition has also been described as occult recurrent subluxation, rela- tive instability, functional instability, or microinstability (62,102,103,106,107). The clinical presentation can be con- fusing due to nonspecific symptoms and equivocal signs at physical exam- ination. Imaging findings may also be subtle or equivocal (63). When imaging is requested, referring physicians may question the presence of , impingement, or superior labral tear rather than implicate instability (103). Because the clinical indications can be misleading, radiologists should consider the prospect of glenohumeral instability during the interpretation of most shoulder MR imaging studies per- formed in young adults. Three major etiologic subsets may be associated with chronic instability in the absence of repeated disloca- tion: remote trauma (including pre- vious first-time dislocation), overuse activity, and generalized capsular lax- ity (62,63,78,102,103,107). Remote trauma may be forgotten by patients or dismissed as unimportant if immedi- Figure 9: MR images in a 24-year-old extreme athlete who denied previous dislocation or major shoulder ate, urgent treatment was unnecessary trauma. A, Axial, fat-suppressed T1-weighted MR arthrogram shows increased signal intensity at the labral (103). Subluxation or even dislocation chondral junction (black arrow), as well as a nondisplaced posteroinferior labral tear and a contrast agent– may have occurred without recognition filled chondral defect with a GLAD lesion (white arrow). A small subchondral cyst is found adjacent to the because the shoulder reduced sponta- posterior tear (open arrow). B, On ABER fat-suppressed T1-weighted MR arthrogram, tear of the anteroin- neously (103). Expecting full recovery, ferior labral chondral is made conspicuous (arrow). At the time of initial MR imaging, the patient elected to patients may decide against medical continue competition, forgoing surgical intervention. Repeat MR imaging 2.5 years later was performed due evaluation until persistent symptoms to disability preventing further competition. C, Axial fat-suppressed T1-weighted MR arthrogram shows a and disability necessitates treatment. Bankart lesion and marked displacement of the anteroinferior labral-ligamentous complex (arrow) from the Therefore, MR imaging can be de- glenoid rim. D, ABER fat-suppressed T1-weighted MR arthrogram demonstrates progression to a GLAD injury layed for weeks or months following in the anteroinferior labrum with detachment and displacement of a large labral chondral fragment (arrow). the traumatic event. Unrecognized dis- Arthroscopic stabilization procedure was performed. The posteroinferior labral chondral GLAD lesion appears location puts the shoulder at risk for to have healed in the interval. the same labral-ligamentous injuries as recognized first-time dislocation Labral-ligamentous injuries, including improves diagnostic accuracy because (102,103). The delay in imaging en- Bankart lesion, Perthes lesion, and contrast material can fill the labral de- ables the resolution of bone marrow HAGL lesion, can be overlooked in the fects in nondisplaced lesions and out- edema and effusion, the healing and absence of Hill-Sachs defect or other os- line abnormal capsular contours (64). remodeling of capsular defects, and the seous evidence for previous dislocation ABER positioning may further increase scarring of nondisplaced labral frag- (20,21,64,74). Compared with conven- diagnostic confidence by transmitting ments to the glenoid rim (65,80,81). tional MR imaging, MR arthrography tension from the IGL to the labrum,

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thereby displacing an occult lesion from are exacerbated by numerous factors, the characterization of lesions for treat- the glenoid rim or revealing an intact including repetitive overstretching, ment planning. Therefore, the decision periosteal sleeve (101) (Fig 2). proprioceptive imbalance, and connec- to use CT, CT arthrography, MR, or MR Overuse represents another impor- tive tissue deficiency (24,63). Patients arthrography also depends on the clini- tant etiologic category in the develop- typically complain of functional limita- cal scenario and goal of imaging. ment of occult recurrent glenohumeral tions due to involuntary glenohumeral Disclosures of Conflicts of Interest: J.T.B. Au- subluxation. Although athletes and phy- instability (111). There is no history of thor stated no relevant conflicts of interest to sicians are less likely to consider the instigating trauma. At physical exami- disclose. S.G. Author stated no relevant conflicts diagnosis of instability in the absence nation, the shoulder is unstable in more of interest to disclose. W.E.P. Author stated no relevant conflicts of interest to disclose. of contact trauma, pitchers, swimmers, than one direction (multidirectional), tennis players, and weight lifters all which helps to differentiate AMBRI may present with functional instability from traumatic unidirectional instability References manifested only as pain (62,103–108). (63,73,111). The opposite shoulder may 1. Lippitt S, Matsen F. Mechanisms of gleno- Repetitive noncontact activities create also feel loose. Surgery, which typically humeral joint stability. Clin Orthop Relat cumulative stresses on both the passive involves capsulorrhaphy or inferior cap- Res 1993;(291):20–28. and dynamic structures that stabilize sular shift, is considered if conservative 2. Dumont GD, Russell RD, Robertson the shoulder (103–106,108). These sta- treatment and rehabilitation fail (111). WJ. Anterior shoulder instability: a re- bilizing structures gradually fail, leading At arthroscopy, the most common find- view of pathoanatomy, diagnosis and to the development of chronic instabil- ing is capsular redundancy in the axil- treatment. Curr Rev Musculoskelet Med ity. Structural failure may result from lary pouch (113). Therefore, the imag- 2011;4(4):200–207. stretching of the inferior glenohumeral ing diagnosis of AMBRI is challenging 3. Mohtadi NG. Advances in the understand- ligament and joint capsule, tearing because labral tears and osseous de- ing of anterior instability of the shoulder. of the anteroinferior glenoid labrum, fects are typically absent (111,112). MR Clin Sports Med 1991;10(4):863–870. and/or delamination of the articular arthrography, and in some instances CT 4. Abboud JA, Soslowsky LJ. Interplay of the cartilage over the anteroinferior glenoid arthrography, may suggest the presence static and dynamic restraints in glenohumer- fossa (62,102–104,106,107). Whereas of capsular redundancy, but reliable cri- al instability. Clin Orthop Relat Res 2002; some overuse lesions may be subtle teria are lacking (114). (400):48–57. and easily overlooked on MR images, 5. O’Connell PW, Nuber GW, Mileski RA, others may be obvious and lead to the Lautenschlager E. The contribution of the Conclusion overestimation of their physiologic sig- glenohumeral ligaments to anterior stabil- nificance (104–106,108). In the symp- Glenohumeral instability encompasses ity of the . Am J Sports Med tomatic overhead athlete, for example, a broad spectrum of clinical complaints 1990;18(6):579–584. stretching of the joint capsule may not and presentations. The diagnosis can 6. Turkel SJ, Panio MW, Marshall JL, Girgis be detectable on MR images, but causes be obvious to the referring physician, FG. 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In not be interpreted as a sign of insta- pitchers, anteroinferior labral tear may bility without other supporting abnor- 8. Moore SM, Ellis B, Weiss JA, McMahon PJ, Debski RE. The glenohumeral capsule actually represent an adaptive change malities (110). Imaging findings depend should be evaluated as a sheet of fibrous that improves performance by allow- on the clinical scenario: acute first-time tissue: a validated finite element model. ing a greater degree of ABER during shoulder dislocation, chronic instability Ann Biomed Eng 2010;38(1):66–76. the late cocking and early acceleration with repeated dislocation, or chronic 9. Pouliart N, Gagey OJ. The arthroscopic phases of throwing (104,105,108). instability without repeated disloca- view of the glenohumeral ligaments com- The third etiologic subset includes tion. Imaging abnormalities that occur pared with anatomy: fold or fact? J Shoul- patients with the atraumatic onset of in the acutely traumatized shoulder are der Surg 2005;14(3):324–328. multidirectional, bilateral laxity or in- substantially different from those that 10. Burkart AC, Debski RE. Anatomy and stability (AMBRI) for which rehabili- typify the chronic unstable joint. The function of the glenohumeral ligaments in tation has a primary role in treatment goal of imaging depends on the clini- anterior shoulder instability. Clin Orthop rather than surgery (59,111,112). In cal scenario. Image interpretation and Relat Res 2002;(400):32–39. AMBRI, developmental capsular lax- reporting may need to emphasize the 11. Beltran J, Bencardino J, Padron M, Shank- ity and glenohumeral hypermobility identification of lesions for diagnosis, or man S, Beltran L, Ozkarahan G. The

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