Skeletal Radiol (2004) 33:617 626 DOI 10.1007/s00256-004-0836-0 R E V I E W A R T I C L E Mahvash Rafii Non-contrast MR imaging of the glenohumeral joint. Part II. Glenohumeral instability and labrum tears Received: 3 May 2004 Revised: 24 June 2004 Accepted: 28 June 2004 Published online: 16 September 2004 ISS 2004 Part I of this Review Article Non-contrast MR imaging of the glenohumeral joint: Normal anatomy appeared in the previous issue (Number 10/Oct. 2004). See also: http://dx.doi.org/10.1007/s00256-004- 0835-1 M. Rafii () ) Department of Radiology, NYU School of Medicine, NYU Medical Center, 560 First Avenue, New York, NY 10016, USA e-mail: Mahvash.rafii@med.nyu.edu Tel.: +1-212-2637636 Fax: +1-212-2636634 Abstract MR imaging of the shoulder without contrast is frequently used for evaluation of glenohumeral instability in spite of the popularity of MR arthrography. With proper imaging technique, familiarity with normal anatomy and variants as well as knowledge of the expected pathologic findings high diagnostic accuracy may be achieved. Keywords MR imaging Glenohumeral joint Labrum tear Glenohumeral instability Introduction Glenohumeral joint instability is recurrence of subluxation or dislocation; it is classified based on etiology (traumatic vs. atraumatic), severity (dislocation, subluxation) and direction of instability (unidirectional in anterior or posterior direction, multidirectional) [1, 2, 3, 4]. Traumatic instability follows an incident of injury, either dislocation or subluxation, and is associated with a high incidence of recurrence in young individuals. Atraumatic instability, which is often multidirectional, occurs in patients with predisposing factors such as congenital capsular laxity or glenoid hypoplasia. A similar form of instability is seen in athletes who participate in throwing sports and swimming; this essentially traumatic instability is due to repetitive microtrauma and is characteristically multidirectional. Functional instability refers to sensation of instability without a discernible clinical instability; the underlying abnormality consists of an isolated tear of the glenoid labrum [5]. Matsen et al. divide glenohumeral instabilities into two groups: the TUBS group includes patients with Traumatic Unidirectional instability with Bankart lesion who require Surgical intervention; the AMBRI group includes Atraumatic patients with Multidirectional and Bilateral instability who often receive Rehabilitation treatment or otherwise an Inferior capsular shift procedure [6]. Patients with traumatic anterior glenohumeral instability comprise more than 95% of instability patients seen in clinical practice.
618 Fig. 1A C Acute Bankart lesion, left shoulder, in a 17-year-old high school basketball player. A Axial proton density image at the junction of the mid- and inferior glenohumeral joint demonstrates the anterior capsulolabral complex detached from the glenoid (arrow). B Axial proton density fat-suppressed image below A better demonstrates the abnormal signal intensity indicating the detachment of the complex extending under the labrum and along the anterior scapular cortex (arrowheads). There is leakage of joint effusion/hemarthrosis beyond the joint capsule (arrow). C T2 weighted fat-suppressed oblique coronal image shows rupture of the scapular periosteum (arrow) Anterior glenohumeral instability Traumatic anterior glenohumeral dislocation or subluxation occurs when there is an applied force to the arm with the humerus in abduction and external rotation, or when the force is applied directly to the back of the shoulder. Both mechanisms result in tensile failure of the anterior capsulolabral complex [7, 8]. The soft tissue lesion most often encountered in the young is the detachment of the anteroinferior capsulolabral complex from the glenoid margin, the so-called Bankart lesion [7]. In the elderly, a high incidence of rotator cuff tear is encountered and recurrence is uncommon [9]. Biomechanical studies demonstrate that capsular failure less commonly involves the humeral attachment of the anteroinferior glenohumeral ligament or may damage the mid-substance of the capsule. These studies, in addition, conclude that plastic deformation of the inferior glenohumeral ligament is needed for anterior instability to occur and such ligamentous strain may result in a permanently stretched ligament [8]. MR imaging findings MR imaging of the shoulder is frequently performed when recurrence is established and often little or no joint effusion is present; the diagnosis is primarily based on morphologic and signal abnormalities of the capsulolabral complex. The Bankart lesion by definition involves the origin of the anterior inferior glenohumeral ligament along the anterior inferior quadrant of the glenoid and includes tearing of the scapular periosteum. The specific MR imaging abnormality, which reflects the detachment of the Fig. 2 Longstanding anterior glenohumeral instability with a Bankart lesion. Axial gradient echo image at the inferior glenohumeral joint, left shoulder: a small and deformed remnant of the anterior labrum remains adjacent to the glenoid margin (arrow) anteroinferior capsulolabral complex, is a zone of increased signal intensity at the glenolabral junction, which extends beyond the glenoid hyaline articular cartilage and through the peripheral glenoid attachment of the labrum (Fig. 1). The detached labrum may, according to the severity of injury or duration of instability, show mild to severe signal and morphologic abnormality; it may be irregular, diminutive or absent (Fig. 2). The detachment may involve only a small segment of the complex or may extend
619 Fig. 3A, B Longstanding anterior glenohumeral instability of the left shoulder with a Bankart lesion. A Axial gradient echo at the inferior glenoid humeral joint. The anterior glenoid labrum at this level is not visualized and there is productive change at the capsule scapular junction representing granulation and scar (arrow). B T2- weighted oblique coronal image. The productive changes resemble an ALPSA lesion Fig. 4A, B Perthes lesion. Gradient echo axial images at the inferior glenohumeral joint. A There is healing of the scapular periosteum; the torn labrum is manifested by a notch deformity at the articular margin of the glenoid (long arrow). Note the redundancy of the capsule/glenohumeral ligament (short arrows). B Axial image below A demonstrates a deficient osseous glenoid margin (arrow) deep to the scapular neck. Rupture of the capsule/scapular periosteum in Bankart lesion results in granulation tissue and ectopic bone formation (Fig. 3). Bankart variations Bankart variations are recognized when the scapular periosteum is detached but not ruptured. In Perthes variant a pouch is formed anteriorly [10]. This pouch may be obscured by healing of the periosteum, leaving a notched deformity at the articular aspect of the labrum (Fig. 4). In ALPSA lesion (Anterior Labroligamentous Periosteal Sleeve Avulsion), the torn labrum rolls on the stripped periosteum and is displaced medially against the scapular margin (Fig. 5). Neviaser emphasizes the need to recognize this lesion which, when synovialized, is obscured at surgery [11]. He recommends detaching the displaced labrum so that a proper Bankart repair is performed. Capsular tears After multiple episodes of anterior glenohumeral instability, the anterior band of the anteroinferior glenohumeral ligament is poorly defined against the subscapularis scapular cortex and the normal pericapsular fat is absent (Fig. 6A); an ill-defined zone of intermediate signal may be observed in the anterior inferior capsular space representing the stretched and redundant ligament (Fig. 6B). Another finding in a non-distended joint includes a wavy outline of the inferior glenohumeral ligament (Fig. 4A). A capsular defect in the rotator interval region may develop which is at times large enough to require surgical closure to ensure successful capsular repair (Fig. 7). This capsular defect is the vicinity and confluent with the opening of the subscapularis recess. Injuries of the capsular substance, other than that associated with a Bankart lesion, may extend beyond the scapular attachment and are well visualized by non-contrast MR imaging. In acute injury, capsular substance tear or strain is visualized as thickening and increased signal
620 Fig. 5A, B ALPSA lesion. A Axial and B oblique coronal T2-weighted images of the right shoulder demonstrate the detached anterior inferior capsulolabral complex, which is displaced medially and inferiorly (arrows) Fig. 6A, B Axial proton density images, same case as Fig. 2. A This axial image below Fig. 2 image demonstrates absence of the anterior labrum and a slightly deficient osseous glenoid margin. The capsule is ill defined and the pericapsular fat is not visualized (arrow). B Axial image below A in addition shows intermediate signal tissue in the glenohumeral space representing a redundant capsule (arrow) intensity of the capsule. Pericapsular edema is often present. A distorted capsule and extensive pericapsular edema/hemorrhage develop with capsular rupture. HAGL lesion Biomechanical studies show that HAGL lesion (Humeral Avulsion of the Glenohumeral Ligament) is the least common type of capsular failure in anterior instability [8]. This lesion is seen in the middle-aged patient who experiences first-time dislocation and may be associated with a tear of subscapularis tendon [12, 13]. In two large series the clinical incidence of HAGL lesion has been reported as 7.5% and 9.4%. Bui-Mansfield et al. reported associated lesions with HAGL to include rotator cuff tear, mostly of the subscapular tendon, tear of the anterior labrum and osteochondral injury of the humeral head [13]. In 20% bone avulsion is present and is referred to as BHAGL lesion [14]. MR imaging when performed soon after injury shows disruption of the axillary pouch in the proximity of the surgical neck of the humerus with surrounding soft tissue edema. These findings are best visualized on T2-weighted oblique coronal images (Fig. 8). A floating anteroinferior glenohumeral ligament sign refers to the association of HAGL lesion with a Bankart lesion [15, 16] (Fig. 9). In chronic cases the presence of a subscapularis tear and pertinent history of trauma should alert the radiologist to this type of capsular injury. GLAD lesion Neviaser first described GLAD lesion (Glenoid Labrum Articular Disruption), with the mechanism of injury as forced adduction of the shoulder from an abducted and externally rotated position [17]. Patients present with anterior shoulder pain but without discernible instability on clinical examination. At surgery and on MR imaging a combination of superficial tear of the anteroinferior la-
621 Humeral head Impaction against the anterior glenoid surface or margin results in a compression fracture of the superoposterior aspect of the humeral head, the so-called Hill Sachs lesion [18, 19]. This lesion is seen with almost all dislocations but less frequently in subluxations and may be limited to a chondral lesion. Subchondral signal abnormality of the humeral head reflecting sclerosis and cystic changes in the chronic stage and bone marrow edema in the acute stage may be observed (Fig. 11). Posterior and multidirectional instability Fig. 7 Rotator interval defect, same case as Fig. 4. Oblique coronal T2-weighted image shows a defect of the rotator interval capsule (arrows) brum and chondral injury of the adjacent glenoid articular cartilage is observed (Fig. 10). Osseous lesions Glenoid An osseous Bankart lesion includes a fracture of the anterior inferior glenoid margin. Recognition of this fracture is significant because of its surgical implications. In patients with a soft tissue Bankart lesion, over time and with increasing episodes of recurrence, the glenoid margin is often eroded. Traumatic posterior dislocation of the shoulder is uncommon and recurrence is a rare event. The mechanism includes injury with the arm in adduction and internal rotation. It may result from violent muscle contractions in electric shock and seizure disorder or direct injury to the shoulder. Posterior instability in the form of recurrent subluxation is increasingly recognized as a cause of pain and shoulder disability, particularly in the young athlete [20]. The mechanism of injury is an incident of macrotrauma or repetitive applied athletic force (swimming, throwing or punching) of the adducting, flexing and internally rotating humerus. Posterior instability in the form of unidirectional recurrent subluxation, however, is exceedingly uncommon; it is often seen as bi-directional, posteriorly and inferiorly or multidirectional instability with an anterior component [21, 22]. In these instances the primary direction of instability is posteriorly. On MR imaging, findings may be subtle and vary from minor tears of the labrum to, uncommonly, a detached capsulolabral complex (reverse Bankart) [23]. An impaction injury of the anterior humeral head may be present; in chronic stage as a groove, and in acute stage as bone marrow edema without or with osteochondral sur- Fig. 8A, B HAGL lesion. A Axial gradient echo image of the right shoulder demonstrates tearing of the humeral attachment of the anterior capsule as well as abnormal signal intensity of the subscapularis tendon (arrow). B Oblique coronal T2- weighted fat-suppressed image demonstrates an abnormal configuration and increased signal intensity at the surgical neck insertion of the capsule (arrow)
622 Fig. 9A, B Floating inferior glenohumeral ligament. A Axial gradient echo image shows a torn humeral attachment of the inferior glenohumeral ligament (long arrow) as well as a Bankart lesion (short arrow). B Oblique coronal T2-weighted fat-suppressed image shows the floating ligament (arrow) Fig. 10A C GLAD lesion, same case as Fig. 14. A Axial proton density and B proton density fat-suppressed images at the inferior glenohumeral joint. The anterior inferior labrum is detached from the articular aspect of the glenoid margin (long arrows). Note the presence of an articular cartilage defect adjacent to the detached labrum (well visualized on Fig. 14). C T2-weighted fat-suppressed oblique coronal image shows the loose chondral fragment in an axillary pouch (arrow) face abnormality (Fig. 12). POLPSA lesion (POsterior Labrocapsular Periosteal Sleeve Avulsion) has been recently described [24]. Posterior glenoid rim fracture and erosion are uncommon findings. Posterior glenoid deficiency as a developmental abnormality may be present and contribute to posterior instability [25]. Bennett lesion Bennett lesion is thickening and ectopic bone formation of the posterior capsule found in baseball players and is often associated with posterior labrum tears [26, 27] (Fig. 13). Superior glenoid labrum tears Andrews first recognized tears of the superior labrum segment in baseball players and implicated forceful contraction of the long head of the biceps tendon as the etiology [28, 29]. Snyder et al. described traumatic tears of the superior labrum, which span from anterior to posterior to biceps anchor, in 1990 and later reported on a large series of patients [30, 31]. He noted the mechanism of injury as a fall on an outstretched hand and described four types of the so-called SLAP lesion at arthroscopy. These are: type 1, simple fraying of the labrum; type 2, fraying and stripping of the labrum including the biceps anchor from the glenoid margin; type 3, bucket-handle tear of the labrum with displacement of the central portion into the joint: and type 4, a more severe bucket-handle tear of the labrum with longitudinal extension into the biceps tendon. Maffet et al. described three additional types: type 5, association with and continuity with a Bankart lesion;
623 Fig. 11A, B Hill Sachs lesion, two cases. A Axial gradient echo image at the superior glenohumeral joint shows the characteristic location and appearance of the bony defect of the articular surface of the humeral head (arrow). B Proton density oblique coronal image of the right shoulder, posterior aspect. A superficial Hill Sachs lesion is better seen in this plane (arrow). Subcortical cystic change is present in the greater tuberosity (arrowhead) Fig. 12A, B Posterior instability with a reversed Bankart lesion. A Gradient echo axial image of the right shoulder. Detachment of the posterior labrum and capsule from the glenoid margin is demonstrated (arrow). B Oblique sagittal T2- weighted fat-suppressed image shows bone contusion and bone marrow edema of anterior humeral head (arrow) type 6, a flap tear of the superior labrum; and type 7, anterior extension into the middle glenohumeral ligament [32]. Morgan in 1998 introduced a subclassification of Snyder type 2 lesion into: 2a, anterosuperior tear; 2b, posterosuperior tear; and 2c, anterior to posterior or same as the conventional SLAP 2 tear [33]. Additional SLAP types (currently up to 10 types), which represent combinations of SLAP lesion with posterior labral tears or extension into the rotator interval ligaments have been described in the radiology literature [34, 35]. The diagnostic accuracy of MR imaging for SLAP lesions without or with contrast is relatively high, although most authors do not attempt to classify lesions [36, 41]. The difficulty stems from the anatomic variation of sublabral recess, which may simulate pathology, as well as lack of clearcut imaging findings; the torn labrum often shows generalized increased signal, particularly on T1- weighted images, which may obscure the actual tear. Several MR imaging findings of SLAP lesion are reported, including signal abnormality in the form of globular or linear signal, single or double (single or double oreo cookie) or a clearly displaced fragment [42]. Signal abnormalities posterior to the biceps anchor and lateral orientation of linear signal are considered highly specific [40]. In approaching superior labral tears comparison with meniscus lesions and Bankart tears is helpful. Type 1 SLAP lesion at arthroscopy is a frayed labrum which is stable and of little clinical significance. This type is the most frequent lesion included in large series. At MR imaging the labrum may show an irregular or ill-defined margin or non-linear intra-labral intermediate signal intensity on T1-weighted or proton density (PD)-weighted images without signal on T2-weighted images. Type 2 SLAP lesions are the most common of the remaining
624 Fig. 13 Bennett lesion. Gradient echo axial image of the right shoulder demonstrates a tear of the posterior labrum with adjacent glenoid cartilage deficiency (long arrow). There is marked thickening of the glenoid attachment of the posterior capsule (arrows) therefore smooth, as opposed to the wider and irregular interface seen in a traumatic lesion. The detached labrum may show additional globular or linear signal. A normal labrum in the young, even with a recess, is more likely to be a signal void than a detached labrum, which often shows additional signal abnormality. Type 3 SLAP lesion is a bucket-handle tear and is therefore seen as a linear, vertically oriented intermediate signal through the labrum surfaces (Fig. 15). Type 4 lesion is a tear which extends from the articular aspect of the biceps anchor into the biceps tendon forming a linear signal parallel to the superior surface of the tendon (Fig. 16). The potentially unstable fragments of these latter types need to be debrided, or reattached, as they may result in abnormal function of the joint. Ultimately, with prevalence of true SLAP lesions in the young and athletic population, and the higher frequency of sublabral recess in the elderly, attention to signal changes specific to SLAP tears and alterations due to aging as well as the patient s age and correlation with the injury pattern are important factors in diagnosing SLAP lesions. Technically, PD oblique coronal images are preferable to T1-weighted images in that they reduce the signal from the degenerated labrum, increasing the contrast with the actual tear. Paralabral and ganglion cyst Fig. 14 Type 2 SLAP lesion. Proton density oblique coronal image. Complete detachment of the superior labrum/biceps anchor (long arrow) from the glenoid (short arrows) is noted. A wide zone of intermediate signal separates the two three types; these lesions are potentially unstable yet difficult to distinguish from a sublabral recess. Type 2 SLAP is essentially a detachment of the superior labrum/ biceps anchor from the glenoid margin. In this respect, this lesion resembles a Bankart lesion and is distinguished with a zone of signal abnormality at the glenolabral junction on all sequences (Fig. 14). Differentiation from a sublabral recess is possible by attention to subtle differences; the recess is narrow and synovial-lined and Paralabral and ganglion cysts of the glenohumeral joint are most commonly seen in the posterior superior aspect of the joint and are presumed to be post-traumatic lesions; they are frequently associated with a labrum tear in their vicinity [43]. Paralabral cysts may present as intralabral cystic change, a small cyst adjacent to the labrum, interposed between the labrum and the capsule, or extend or form a ganglion cyst periarticularly. A well-known complication associated with ganglion cyst is compression of the suprascapular neurovascular bundle, which may result in entrapment of the nerve and malfunction of the supraspinatus and infraspinatus muscle tendon units. The patient presents with nonspecific pain and abnormal function of the glenohumeral joint [44]. Internal impingement Internal impingement or posterosuperior impingement of the glenohumeral joint is the association of posterior superior labrum tear with undersurface tearing of the rotator cuff in the vicinity. This lesion is seen with anterior laxity of the glenohumeral joint and is the result of impingement of the rotator cuff on the posterior superior glenoid when the arm is externally rotated and extended [45, 46].
625 Fig. 15A, B Type 3 SLAP lesion. T2-weighted fat-suppressed oblique coronal images of the right shoulder. Detachment of the biceps anchor from the superior glenoid margin (thick arrow) is demonstrated. The tear extends to the superior surface of the anchor (thin arrow) indicating presence of a type 3 SLAP Fig. 16A, B Type 4 SLAP lesion. A Oblique coronal T2-weighted fat-suppressed image of the left shoulder demonstrates a tear of the superior labrum/biceps anchor. High signal intensity at the glenolabral junction (short arrow) is seen. The longitudinal extension into the bicep anchor is noted by focal irregularity at the superior surface of the anchor as well as difference in signal intensity of the two segments (long arrow). B Oblique sagittal T2-weighted fatsuppressed image shows the longitudinal split of the long head of the bicep tendon beyond the bicep anchor (arrow) References 1. Coefield RH, Irving JF. Evaluation and classification of shoulder instability with reference to examination under general anesthesia. Clin Orthop 1987; 223:32 43. 2. Matsen FA, Harryman DT, Sidles JA. Mechanics of glenohumeral instability. Clin Sports Med 1990; 10:783 788. 3. Neer CS II, Foster CR. Inferior capsular shift for involuntary inferior and multidirectional instability of the shoulder. A preliminary report. J Bone Joint Surg Am 1980; 62:897 908. 4. Levine WN, Flatow EL. The pathophysiology of shoulder instability. Am J Sports Med 2000; 6:910 917. 5. Pappas AM, Goss TP, Kleinman PK. Symptomatic shoulder instability due to lesions of the glenoid labrum. Am J Sports Med 1983; 11:279 288. 6. Rockwood CA, Matsen FA. Anterior glenohumeral instability. In: Rockwood CA, Matsen FA, eds. The shoulder. Philadelphia: WB Saunders, 1990:526 551. 7. Bankart ASB. The pathology and treatment of dislocation of the shoulder joint. Br J Surg 1938; 26:23 29. 8. Bigliani L, Pollock R, Soslowsky L, et al. Tensile properties of the inferior glenohumeral ligament. J Orthop Rel Res 1992; 10:187 197. 9. Neviaser RJ, Neviaser TJ, Neviaser JS. Concurrent rupture of the rotator cuff and anterior dislocation of the shoulder in the older patient. J Bone Joint Surg Am 1988; 70:1308 1311. 10. Perthes G. Über operationen bei habitueller Schulterluxation. Dtsch Z Chir 1906; 85:199 227.
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