Imaging 15:174-179 (2003)
© 2003 The British Institute of Radiology
Glenohumeral instability
C McCarthy, FRCR
Nuffield Orthopaedic Centre and Oxford Radcliffe Hospital, Oxford, UK
Glenohumeral instability refers to symptomatic subluxation or dislocation of the humeral head in relation to the glenoid fossa. Anteroinferior instability is the most common type to involve the glenohumeral joint, occurring in 95% of all patients [1]. The remaining 5% of patients have posterior (3%), inferior, superior or multidirectional instability [1]. Fractures of the osseous glenoid and humeral head as well as tears of the labroligamentous complex are frequently associated features. MR arthrography is increasingly recognised as the examination of choice in glenohumeral instability providing excellent depiction of associated intra-articular lesions. In a study of 121 subjects with surgically proven labral injuries, Palmer and Caslowitz reported a sensitivity of 92% and a specificity of 92% for the MR arthrographic detection of labral tears [2]. This is further improved by the addition of stress views, using the abducted and externally rotated (ABER) position, in which the patient is imaged with the arm resting under the neck and oblique axial images are acquired parallel to the long axis of the humeral shaft. Imaging in the ABER position is reported to increase the sensitivity and specificity for anterior labral injury detection to greater than 95% [3].
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Classification
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Two main categories of instability are generally considered on the basis of the mechanism, directionality, and preferred method of treatment [1]. The first category is traumatic unidirectional Bankart surgery (TUBS), which is characterized by a history of trauma resulting in unidirectional anteroinferior instability, commonly associated with a fibrous or osseous Bankart lesion that requires surgical repair. The second category is known as atraumatic multidirectional bilateral rehabilitation inferior capsular shift (AMBRI). This pattern of multidirectional instability, usually involving both glenohumeral joints, is believed to be the result of atraumatic ligamentous and capsular laxity. Treatment is rehabilitation initially followed by inferior capsular shift if indicated.
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Anterior glenohumeral instability
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Anteroinferior labral tear
Anterior labral tears most commonly involve the anteroinferior aspect of the glenoid labrum [4, 5] secondary to anteroinferior dislocation or subluxation which produces a constellation of lesions [5, 7]. Avulsion of the labroligamentous complex from the anteroinferior aspect of the glenoid, with complete disruption of the scapular periosteum, is termed a fibrous Bankart lesion (Figure 1
). The presence of an associated adjacent glenoid rim fracture is referred to as an osseous Bankart lesion (Figure 2). A Hill-Sachs impaction deformity or fracture involving the posterosuperior humeral head is a frequently associated finding [1, 5–7].
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Figure 1. Fibrous Bankart lesion. An axial T1 weighted spin echo MR arthrographic image with fat saturation, at the level of the inferior glenoid labrum, demonstrates the avulsed and displaced labroligamentous complex from the anteroinferior aspect of the glenoid, with complete disruption of the scapular periosteum, which constitutes the fibrous Bankart lesion (arrow).
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Figure 2. Bony Bankart lesion. A fracture through the anteroinferior aspect of the bony glenoid rim is well depicted on this axial CT image which together with an avulsed anteroinferior labrum is referred to as an osseous Bankart lesion.
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A number of variants of the Bankart lesion, where the periosteum remains intact, have been described.
(1) The anterior labroligamentous periosteal sleeve avulsion (ALPSA) lesion is characterized by the torn anteroinferior labrum being displaced inferomedially by the inferior glenohumeral ligament and rolling up like a sleeve (Figure 3). The displaced labrum remains attached to the scapula via an intact anterior scapular periosteum [1, 5–7]. Healing by fibrosis may occur in an abnormal anatomical location leaving a deformed and redundant labrum [5–7].
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Figure 3. ALPSA lesion. Axial T2* gradient echo MR arthrographic image with fat saturation of an anterior labroligamentous periosteal sleeve avulsion (ALPSA) lesion. The torn anteroinferior labrum remains attached to the scapula via an intact anterior scapular periosteum and can be seen displaced inferomedially, rolled up like a sleeve on the scapular neck (arrow).
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(2) The Perthes lesion represents a non-displaced avulsed anteroinferior labrum with medial stripping but not disruption of the scapular periosteum (Figure 4). As a result of the redundant intact periosteum, recurrent anterior instability may occur as the humeral head moves into this lax portion of the joint. As the avulsed labrum is not displaced, this lesion may not be detected at standard MR imaging, including MR arthrography [1, 6, 8]. Imaging in the ABER position which stretches the inferior glenohumeral ligament and its labral attachment may result in displacement of the labral tissue and increased diagnostic accuracy of these lesions [6, 8].
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Figure 4. Perthes lesion. An axial T1 weighted spin echo MR arthrographic image with fat saturation shows an undisplaced avulsed anteroinferior labrum with medial stripping of an intact scapular periosteum consistent with a Perthes lesion (arrow). This lesion is better visualized when stress is applied such as during abduction and external rotation.
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(3) The glenolabral articular disruption (GLAD) lesion refers to an anteroinferior labral tear, which is held in place by an intact anterior scapular periosteum, with an adjacent glenoid articular cartilage injury (Figure 5) [1, 5–7, 9]. The pattern of chondral injury can range from a cartilaginous flap tear to a depressed osteochondral injury of the articular cartilage and the underlying bone [9]. This lesion results from impaction of the humeral head against the glenoid rather than from dislocation and is usually a stable lesion because of the non-displaced labrum and intact inferior glenohumeral ligament [1, 9].
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Figure 5. GLAD lesion. A glenolabral articular disruption (GLAD) lesion is well shown on this axial T1 weighted spin echo MR arthrogram with fat saturation. Note the anteroinferior labral tear, with an attached fragment of adjacent articular cartilage, which is held in place by an intact anterior scapular periosteum (arrow).
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Extensive anterior labral tear
The second most frequent location of a labral tear involves the entire anterior labrum, from the base of the biceps tendon to the insertion of the inferior glenohumeral ligament [4, 5, 7].
Anterosuperior labral tear
Isolated tears of the anterosuperior labrum are uncommon and in the absence of other pathological findings, the possibility that they represent normal anatomical variants should be considered [4, 5, 7].
Glenohumeral ligament injury
Anterior glenohumeral instability can involve tears of the glenohumeral ligaments. The inferior glenohumeral ligament consists of an anterior band, a posterior band and an interposed axillary pouch. Injuries to the anterior band are more likely to be associated with clinically evident instability as this band is the single most important stabilizer of the glenohumeral joint and should receive careful attention during MR image analysis [1]. The humeral avulsion of the glenohumeral ligament (HAGL) lesion is an avulsion of the anterior band of the inferior glenhumeral ligament at or near its humeral attachment with inferomedial retraction of the ligament which appears thick and irregular [1]. In 20% of cases, a medial humeral avulsion fracture (BHAGL) is present [10]. Rarely, a floating avulsion of the inferior glenohumeral ligament (AIGHL) lesion occurs where there are simultaneous avulsions at both the glenoid and humeral sites of insertion of the anterior band [10].
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SLAP lesion
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The superior labral anteroposterior (SLAP) lesion is a superior labral tear that extends both anterior and posterior to the biceps tendon attachment and most commonly results from repetitive traction to the biceps tendon as seen in throwing athletes. The original classification described four types of SLAP lesions depending on the degree of involvement of the long head of biceps tendon and the labrum, although several additional types have subsequently been described. Type I is characterized by superior labral degeneration and fraying, type II, the most common of all SLAP lesions, consists of avulsion of the superior labrum and long head of biceps tendon from the glenoid (Figure 6), type III is seen as an inferiorly displaced bucket handle superior labral tear with an intact biceps anchor and type IV involves extension of a bucket handle superior labral tear into the proximal long head of the biceps tendon [1, 4, 5, 7, 11]. As surgical treatment is based on compromise of the biceps anchor, precise classification is less useful than knowledge about the presence and extent of biceps tendon involvement [6].
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Figure 6. Type II SLAP lesion. Coronal oblique T2* gradient echo MR arthrographic image with fat saturation illustrates intra-articular contrast interposed between the avulsed superior labral-biceps complex and the glenoid margin, representing a type II superior labral anteroposterior (SLAP) lesion, which is orientated in a lateral direction away from the glenoid rim (arrow).
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Posterior glenohumeral instability
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At the time of posterior dislocation, tears occurring in the posterior labrum are referred to as a reverse Bankart lesion and impaction of the anterosuperior humeral head gives rise to the reverse Hill-Sachs defect [1, 5–7].
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Paralabral cysts
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Paralabral cysts are lobulated fluid collections that are associated with labral tears and shoulder instability. The cysts arise from extrusion of shoulder joint fluid through labrocapsular tears, the location of the cyst indicating the position of the labral tear. Cyst extension into the spinoglenoid (between the scapular spine and the glenoid cavity) or suprascapular notch may result in muscle atrophy from compression of the suprascapular nerve. If the cyst is positioned in the more usual posterior position then isolated involvement of the infraspinatus is seen (Figure 7) [1, 6, 12].
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Figure 7. Paralabral cyst. (a) Ultrasound and (b) coronal T2 weighted MRI showing a cyst in the suprascapular notch (arrows). (c) Fat infiltration of the infraspinatus muscle indicating atrophy is seen on this T1 weighted coronal image.
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Normal anatomical variants
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Certain normal labral variants must not be confused with true labral abnormalities. If the glenoid articular surface is viewed as the face of a clock, most of the normal anatomical variants occur at the 11 to 3 o'clock position, involving the anterosuperior portion of the labrum. Pathological findings associated with anterior glenohumeral joint instability frequently occur at the 3 to 6 o'clock position.
A sublabral foramen represents normal localized detachment of the anterosuperior labrum from the glenoid [1, 4, 6, 7] at the 2 o'clock position, anterior to the biceps tendon attachment (Figure 8) [4]. A sublabral foramen may be difficult to distinguish from an anterosuperior labral tear. An isolated anterosuperior labral tear is very uncommon [4, 6, 7] and tends to occur in high performance throwing athletes [6]. An appropriate clinical history of pain and instability when throwing together with periosteal detachment and irregularity of the labrum are consistent with an anterosuperior labral tear [5, 7].
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Figure 8. Normal variant. Sublabral foramen. Intra-articular contrast is visualized extending between the anterosuperior labrum and the glenoid margin, reflecting a normal sublabral foramen (arrow). The extent of the foramen is well depicted on this coronal oblique T1 weighted spin echo MR arthrogram with fat saturation.
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The sublabral recess refers to a normal synovial reflection between the cartilage of the glenoid cavity and the superior labrum [1, 4, 6, 7] located at the 12 o'clock position, at the site of attachment of the biceps tendon (Figure 9) [4]. The sublabral recess may be continuous with a sublabral foramen [4]. This variant may be misinterpreted as a superior labral anteroposterior tear (SLAP II lesion) at MRA. The intra-articular contrast which extends into a normal sublabral recess is smooth and tapering, with a width of only 1 mm or 2 mm and usually extends in a medial direction towards the glenoid attachment of the superior labrum. The superior labrum maintains a normal triangular configuration with a sharp free edge and contains no abnormal signal within its substance [1, 4]. In general, SLAP II lesions are orientated in a lateral direction away from the glenoid rim [4, 7, 11] and may extend posterior to the biceps tendon [11]. In addition, there is an increased distance between the glenoid and the superior labrum which has an irregular free margin [4].
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Figure 9. Normal variant. Sublabral recess. Intra-articular contrast fills a normal sublabral recess, seen between the glenoid cavity and superior labrum at the 12 o'clock position, on this coronal oblique T1 weighted spin echo MR arthrographic image with fat saturation (arrow). The sublabral recess is smooth and tapering, extending in a medial direction towards the glenoid attachment of the superior labrum. The superior labrum maintains a normal triangular configuration with a sharp free edge and contains no abnormal signal within its substance.
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The Buford complex is made up of a congenitally absent anterosuperior labrum in association with a thickened cord-like middle glenohumeral ligament [1, 4, 6, 7, 13]. Axial MR images obtained at the level of the superior half of the glenoid depict the cross-section of the thickened middle glenohumeral ligament close to the anterior glenoid margin which has an absent labrum (Figure 10). This combination of findings simulates the appearance of an avulsed anterior labral fragment [7]. Recognition that the apparent detachment is the thickened middle glenohumeral ligament, best identified in the oblique sagittal plane, should aid in avoiding this pitfall [6, 7]. In addition, the biceps anchor and sites of insertion of the superior and middle glenohumeral ligaments are normal [6, 13].
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Figure 10. Normal variant. Buford complex. Axial T1 weighted spin echo MR arthrographic image with fat saturation, obtained at the level of the superior half of the glenoid, illustrates a thickened cord-like middle glenohumeral ligament adjacent to the anterosuperior glenoid rim with a congenitally absent labrum (arrow). This combination of findings comprises a normal Buford complex and must not be confused with an avulsed anterior labral fragment.
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Variations in the anterior capsular insertions have been described. Insertion at the glenoid margin is known as type I, type II refers to insertion at the glenoid neck within 1 cm of the labral base and type III describes an insertion on the scapula more than 1 cm medial to the labral base [6, 7]. Some authors believe that type III insertions are associated with anterior instability [7]. An overdistended capsule at MR arthrography may produce prominent anterior and posterior recesses, falsely simulating a type III insertion and capsular laxity [5].
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References
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- Ly JQ, Beall DP, Sanders TG. MR imaging of glenohumeral instability. AJR Am J Roentgenol 2003;181:203–13.[Free Full Text]
- Palmer WE, Caslowitz PL. Anterior shoulder instability: diagnostic criteria determined from prospective analysis of 121 MR arthrograms. Radiology 1995;197:819–25.[Abstract/Free Full Text]
- Cvitanic O, Tirman PFJ, Feller JF, Bost FW, Minter J, Carroll KW. Using abduction and external rotation of the shoulder to increase the sensitivity of MR arthrography in revealing tears of the anterior glenoid labrum. AJR Am J Roentgenol 1997;169:837–44.[Abstract/Free Full Text]
- De Maeseneer M, Van Roy F, Lenchik L, et al. CT and MR arthrography of the normal and pathologic anterosuperior labrum and labral-bicipital complex. Radiographics 2000;20:S67–S81.[Abstract/Free Full Text]
- Beltran J, Rosenberg ZS, Chandnani VP, Cuomo F, Beltran S, Rokito A. Glenohumeral instability: evaluation with MR arthrography. Radiographics 1997;17:657–73.[Abstract]
- Grainger AJ, Elliott JM, Campbell RSD, Tirman PFJ, Steinbach LS, Genant HK. Direct MR arthrography: a review of current use. Clin Radiol 2000;55:163–76.[Medline]
- Shankman S, Bencardino J, Beltran J. Glenohumeral instability: evaluation using MR arthrography of the shoulder. Skeletal Radiol 1999;28:365–82.[Medline]
- Wischer TK, Bredella MA, Genant HK, Stoller DW, Bost FW, Tirman PFJ. Perthes lesion (a variant of the Bankart lesion). MR imaging and MR arthrographic findings with surgical correlation. AJR Am J Roentgenol 2002;178:233–7.[Abstract/Free Full Text]
- Sanders TG, Tirman PFJ, Linares R, Feller JF, Richardson R. The glenolabral articular disruption lesion: MR arthrography with arthroscopic correlation. AJR Am J Roentgenol 1999;172:171–5.[Abstract/Free Full Text]
- Bui-Mansfield LT, Taylor DC, Uhorchak JM, Tenuta JJ. Humeral avulsions of the glenohumeral ligament; imaging features and a review of the literature. AJR Am J Roentgenol 2002;179:649–55.[Abstract/Free Full Text]
- Bencardino JT, Beltran J, Rosenberg ZS, et al. Superior labrum anterior-posterior lesions: diagnosis with MR arthrography of the shoulder. Radiology 2000;214:267–71.[Abstract/Free Full Text]
- Tirman PFJ, Feller JF, Janzen DL, Peterfy CG, Bergman AG. Association of glenoid labral cysts with labral tears and glenohumeral instability: radiologic findings and clinical significance. Radiology 1994;190:653–8.[Abstract/Free Full Text]
- Tirman PFJ, Feller JF, Palmer WE, Carroll KW, Steinbach LS, Cox I. The Buford complex- a variation of normal shoulder anatomy: MR arthrographic imaging features. AJR Am J Roentgenol 1996;166:869–73.[Abstract/Free Full Text]
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Classification
Anterior glenohumeral...
