MRI of the Rotator Interval of the Shoulder J.C

Clinical Radiology (2007) 62, 416e423

PICTORIAL REVIEW MRI of the rotator interval of the shoulder J.C. Leea, S. Guya, D. Connella, A. Saifuddina,c,*, S. Lambertb,c

Departments of aRadiology and bOrthopaedics, The Royal National Orthopaedic Hospital NHS Trust, Stanmore, Middlesex, UK, and cThe Institute of Orthopaedics and Musculoskeletal Sciences, University College London, UK

Received 4 July 2006; received in revised form 7 November 2006; accepted 22 November 2006

The rotator interval of the shoulder joint is located between the distal edges of the supraspinatus and subscapularis tendons and contains the insertions of the coracohumeral and superior glenohumeral ligaments. These structures form a complex pulley system that stabilizes the long head of the biceps tendon as it enters the bicipital groove of the humeral head. The rotator interval is the site of a variety of pathological processes including biceps tendon lesions, adhesive capsulitis and anterosuperior internal impingement. This article describes the anatomy, function and pathology of the rotator interval using magnetic resonance imaging (MRI). ª 2007 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.

Introduction edge of the supraspinatus tendon, inferiorly by the superior aspect of the subscapularis tendon, me- The rotator interval of the shoulder refers to the dially by the base of the coracoid process and interspace between the supraspinatus and subsca- laterally by the long head of biceps tendon and its pularis tendons through which courses the long head sulcus (Fig. 1). of biceps tendon. Separate terms have been applied Cadaveric and arthroscopic studies have to the musculotendinous separation around the described the macroscopic constituents of the 2e4 coracoid process (anterior rotator interval) and to rotator interval. The medial rotator interval the separation of the supraspinatus and infraspinatus contains the long head of biceps tendon as it muscles and their corresponding tendons around the inserts into the superior glenoid labrum. As the scapular spine (posterior rotator interval).1 In this biceps tendon passes laterally through the rotator paper, the term rotator interval refers to the anterior interval, it is covered superficially by fibres of rotator interval. This article reviews the relevant the coracohumeral ligament whilst a condensation anatomy, clinical and radiological features of disor- of the superior glenohumeral ligament and the ders of the rotator interval. joint capsule lie deep to it (Fig. 2). The superior glenohumeral ligament, which arises from the supraglenoid tubercle adjacent to the long head The normal rotator interval of biceps tendon, inserts into the lesser tuberosity, forming the anterior covering band of the long Anatomy head of biceps tendon in its sulcus (Fig. 2). The coracohumeral ligament arises from the proximal The rotator interval subtends a medially based third of the dorsolateral aspect of the coracoid triangular space bordered superiorly by the leading process and passes through the rotator interval in union with the superior glenohumeral ligament (Figs. 1 and 2). The coracohumeral ligament fibres * Guarantor and correspondent: A. Saifuddin, Department of then fan out laterally to insert into the greater Radiology, The Royal National Orthopaedic Hospital NHS Trust, Brockley Hill, Stanmore, Middlesex, HA7 4LP, UK. Tel.: þ44 20 tuberosity and bicipital sheath, as well as fusing 8909 5443; fax: þ44 20 8909 5281. with the anterior fibres of supraspinatus and supe- 5 E-mail address: [email protected] (A. Saifuddin). rior fibres of subscapularis tendon insertions. The

and the subscapularis tendon insertion, is referred to as the biceps ‘‘reﬂective pulley’’ or ‘‘sling’’. The principal function of the biceps pulley is to pre- vent medial subluxation of the biceps tendon out of the intertuberculous groove during active move- ment and to increase biomechanical efﬁciency during biceps contraction.

Magnetic resonance imaging (MRI) of the rotator interval

Standard imaging planes for MRI of the shoulder include coronal oblique, sagittal oblique and axial sequences. The oblique sagittal plane, taken parallel to the glenoid fossa and orthogonal to Figure 1 Line drawing of the rotator interval in sagit- the long axis of the rotator interval and cuff, is the tal section. A, acromion process; C, coracoid process; single most valuable sequence to evaluate the H, humeral head; LHBT, long head of biceps tendon; CHL, interval and its contents.6 A combination of proton coracohumeral ligament; SGHL, superior glenohumeral density and T2-weighted (T2W) spin-echo or turbo ligament; sst, supraspinatus tendon; sct, subscapularis spin-echo, high-resolution (<3 mm) sequences tendon. using a high image matrix is recommended. The capsular component of the normal rotator transverse humeral ligament is a broad band that interval passes from the anterior edge of the supra- passes between the lesser and greater tuberosities spinatus tendon to the superior edge of the sub- converting the intertuberculous groove into a canal. scapularis tendon and should be thin, smooth and of The combination of the coracohumeral, superior uniform low signal intensity on the sagittal oblique glenohumeral and transverse humeral ligaments, sequence (Fig. 3). The capsule may be very thin and

Figure 3 Sagittal oblique PD-weighted fast spin-echo MRI image demonstrating the normal rotator interval Figure 2 Diagrammatic representation of the biceps capsule as a thin, hypointense band (arrows) extending reflective pulley system. CHL, coracohumeral ligament; from the anterior margin of supraspinatus to the supe- SGHL, superior glenohumeral ligament; C, coracoid pro- rior margin of subscapularis. The long head of biceps cess; LHBT, long head of biceps tendon; H, humeral tendon (long arrow) is identified between the rotator head; GT, greater tuberosity; LT, lesser tuberosity. interval capsule and the humeral head. 418 J.C. Lee et al. difficult to discern, and the presence of high signal our experience, this extra sequence frequently intensity fluid and/or synovitis will outline the adds little to the diagnosis. Isolated rupture of the structure more clearly. The coracohumeral liga- rotator interval capsule may be missed on axial ment is identified as a single or double hypointense and coronal oblique planes and should be assessed band extending from the posterior aspect of the on the sagittal oblique acquisition.8 coracoid process into the rotator interval (Fig. 4). The biceps tendon can be identified between the rotator interval capsule and the humeral head Function and clinical lesions of the (Fig. 3). In the sagittal oblique plane, the medial rotator interval edge of the long head of biceps tendon lies imme- diately deep to the coracohumeral ligament. The The rotator interval is a defined anatomical space transverse humeral ligament, which forms the lat- but its constituent parts play several important eral boundary of the rotator interval, is optimally roles in the shoulder. Instability of the long head of demonstrated on axial images as a thin hypo- biceps tendon and the glenohumeral joint, as well intense line bridging the bicipital groove (Fig. 5). as synovial changes in adhesive capsulitis, are all The superior glenohumeral ligament may be recognized pathological processes that involve the difficult to define on conventional shoulder MRI, rotator interval. being optimally imaged on axial MR arthrography (MRA; Fig. 6). In fact, some authors believe that all of the structures of the rotator interval are opti- Long head of biceps tendon abnormalities mally imaged using direct MRA. Chung et al.7 per- formed a cadaveric study comparing standard MRI Pulley lesions and MRA on the same shoulder. The authors found The biceps pulley is formed by the intimate that only the extra-articular portion of the long arrangement between the coracohumeral, superior head of biceps tendon was seen in all cases on glenohumeral and transverse humeral ligaments standard MRI whilst on direct MRA, the intra- plus the subscapularis tendon, as mentioned above articular course of the long head of biceps tendon (Fig. 2). These structures act together to form the could also be reliably identified (Fig. 7). In the study medial wall of the superior biceps pulley preventing of Chung et al., the superior glenohumeral ligament medial subluxation of the long head of biceps ten- was not identified at all on standard MRI sequences don. It is important to note that biceps instability and the coracohumeral ligament was seen in only may be due to avulsion of the superior glenohumeral 60% of the specimens, whereas both ligaments ligament/coracohumeral ligament complex, as well were seen in all cases on MRA. Chung et al. also as the more widely recognized tear of the subscapu- recommended a dedicated sequence perpendicular laris tendon. to the coracohumeral ligament/superior glenohum- Disorders of the biceps tendon are optimally eral ligament complex to fully evaluate these imaged using a combination of axial and sagittal structures and the long head of biceps tendon. In T2W sequences.9 Biceps tendon subluxation is

Figure 4 (a) Sagittal oblique T2W fast spin-echo sequence demonstrating the normal coracohumeral ligament as a thin, hypointense band (arrowhead) extending from the posterior aspect of the coracoid process to the rotator interval. The ligament is surrounded by fat. (b) Axial T2*W gradient echo. (c) Coronal PD-weighted fast spin-echo sequences demonstrating the normal coracohumeral ligament (arrows). MRI of the rotator interval of the shoulder 419

Figure 5 Axial T2*W gradient echo MRI image demonstrating the transverse humeral ligament (long arrow) bridging the bicipital groove and covering the long head of biceps tendon (short arrows). Note also the subscapularis tendon (arrowhead). Figure 7 Coronal oblique T1W fat-suppressed direct MR arthrogram demonstrating the entire length of the diagnosed when the tendon is seen to lie on the intra-articular portion of the long head of biceps tendon medial ridge of the bicipital sulcus (Fig. 8) whilst (arrowheads). a dislocated tendon may lie within the subscapula- and medial fibres of the coracohumeral ligament.12 ris tendon (Fig. 9) or come to lie anterior to the 10 Ten percent of supraspinatus tendon tears were subscapularis tendon. Lesions of the reflection associated with involvement of the lateral fibres pulley of the biceps tendon have also been de- of the coracohumeral ligament. Therefore, retrac- scribed with MRA and features include irregularity tion of the subscapularis must infer at least a partial of the superior margin of the subscapularis tendon, tear of the coracohumeral ligament. extra-articular contrast collection and biceps tendon subluxation.11 In one arthroscopic study of ‘‘hidden’’ rotator interval lesions in patients with supraspinatus tendon tears, there was a 27% incidence of subscapularis tears and 47% of these were associated with involvement of the superior glenohumeral ligament

Figure 8 Axial PD-weighted fast spin-echo MRI image demonstrating a partial articular side tear of the subsca- Figure 6 Axial T1W fat-suppressed direct MR arthro- pularis tendon with subluxation of the long head of gram demonstrating the superior glenohumeral ligament biceps tendon (arrow), which is lying on the medial ridge (arrow). of the proximal aspect of the bicipital groove. 420 J.C. Lee et al.

Figure 10 Sagittal T2W fast spin-echo MR image dem- Figure 9 Axial PD-weighted fast spin-echo MRI demon- onstrates a swollen, hyperintense, but intact long head strating an extensive superior surface subscapularis ten- of biceps tendon within the rotator interval, indicative dontearwithmedialdislocationofthelonghead of biceps tendinopathy (arrow). of biceps tendon. The tendon is lying within the deep aspect of subscapularis (arrow). between the tendinous insertion of the subscapula- Biceps tendinopathy and tendon tears ris and the anterior glenoid labrum and rim. Partial Degenerative changes within the biceps tendon are subscapularis tendon tears are the commonest MR 13 commonly associated with rotator cuff tears. arthrographic finding, whilst at arthroscopy an ar- Biceps tendinopathy is diagnosed when there is ticular surface partial tear of subscapularis, usually increased intra-tendinous signal intensity within associated with a pulley lesion, is the commonest a swollen long head of biceps tendon (Fig. 10), finding. This is optimally demonstrated in the ab- and is commonly with associated with synovitis duction external rotation (ABER) position (Fig. 11). and adhesions within the tenosynovial sheath. Par- tial or complete tears of the long head of biceps SLAP lesions tendon tendon are associated with tears of the sub- Tears of the biceps pulley complex may be associ- scapularis and supraspinatus tendons and are iden- ated with injuries to the superior glenoid labrum tified on conventional MRI with a reported accuracy (Fig. 12). In the presence of rotator interval lesions, of 79%.14 Partial tears are diagnosed when there the superior labrum must be carefully assessed is either a longitudinal region of increased intra- on the coronal oblique sequences and should be tendinous signal intensity reaching the edge of a smooth and of uniform low signal intensity on all non-expanded tendon, or when there is an abrupt sequences. High signal intensity within the labrum change in diameter of the long head of biceps ten- raises the possibility of a SLAP lesion, which is don on serial axial images. The lack of biceps ten- associated with tears of the bicipital anchor and don swelling may distinguish partial tears from therefore, the rotator interval.16,17 tendinopathy, but occasionally, it may not be possible to separate the two conditions on MRI. A com- Glenohumeral stability plete tear of the long head of biceps tendon will manifest as an empty biceps tendon sheath. Cadaveric and arthroscopic studies have found that the structures of the rotator interval are important Anterosuperior internal impingement stabilizers of the glenohumeral joint.18,19 Superiore Anterosuperior internal impingement is a recently inferior stabilization of the glenohumeral joint in described condition in which there is shoulder pain the neutral or internally rotated position relies on provoked by anterior elevation and internal rota- maintenance of the intra-articular pressure con- tion of the glenohumeral joint, with no symptoms or ferred by an intact rotator interval capsule.20 A signs of instability.15 Depending upon the degree of missed rotator interval capsular defect may be elevation of the arm, impingement occurs between responsible for recurrent anteroinferior and the long head of biceps tendon and pulley region multidirectional instability, particularly inferior with the superior most aspect of the labrum, or translation in the adducted and internally rotated MRI of the rotator interval of the shoulder 421

Figure 12 Coronal oblique fat-suppressed T1W fast spin-echo direct MR arthrogram image demonstrating a detached tear of the superior glenoid labrum (arrow) extending into the long head of biceps tendon (arrowhead). Figure 11 T2W fast spin-echo direct MR arthrogram in the abduction external rotation (ABER) position showings impingement (curved arrow) between the insertion of subscapularis (straight arrow) and the anterosuperior lesion described by these authors is in fact part aspect of the glenoid labrum (arrowhead). of the emerging syndrome of sub-coracoid impingement (Fig. 13).23 The type II lesion occurs in a younger patient group, and is characterized by arm. Sectioning of the rotator interval capsule in instability with inflammatory change within the cadaveric shoulder joints was found to increase deeper tissues of the rotator interval. ranges of flexion, extension, adduction and external rotation.21 Conversely, imbrication of the capsule reduced the ranges of all these movements. If a rotator interval defect is not closed in a patient with instability, along with the normal capsulorra- phy, then there may be recurrent postoperative symptoms.18,19,21 Detecting and closing a rotator interval defect arthroscopically may be difficult as the rotator interval is regularly used as the anterior portal in shoulder arthroscopy, reducing the chance of discovering lesions of this area.

Type I and II rotator interval lesions Nobuhara and Ikeda first described the term ‘‘rotator interval lesion’’ as a cause of painful shoulder syndrome characterized by inferior instability in the rotator interval.22 The authors defined two sub-types: type I, a contracted state, is characterized by a superficial post-inflammatory contraction of the coracohumeral ligament and Figure 13 Axial T2W GE image obtained in internal ro- subacromial bursa following an injury to the rota- tation showing marked reduction in the space between tor interval. It is possible, with the acceptance the lesser tuberosity (long arrow) and the tip of the that the rotator interval is predominantly responsi- coracoid process (short arrow) with hyperintensity of ble for superioreinferior stability, that the type I the intervening subscapularis tendon. 422 J.C. Lee et al.

Adhesive capsulitis Conclusion

Primary myofibroblastic transformation is thought The rotator interval is a complex anatomical to initiate contracture of the coracohumeral liga- region, which can give rise to a variety of clinical ment component of the rotator interval tissue in symptoms and signs. The imaging features of the early stages of idiopathic frozen shoulder rotator interval lesions are also variable and the (adhesive capsultitis).24 As the rotator interval most subtle rotator interval lesions, consisting of shortens in the mediolateral and craniocaudal small tears of the deep surface of the subscapu- directions the relative gliding of the anterior mar- laris tendon or leading edge of the supraspinatus gin of the supraspinatus tendon and the cranial tendon may easily be overlooked on conventional margin of the subscapularis tendon is restricted MRI unless particular attention is given to this and external rotation range is diminished. In at- region. tempted external rotation the humeral head is then obligatorily displaced downward and back- ward. In attempted sagittal plane flexion the hu- References meral head is displaced inferiorly: the thickened interval tissue can obstruct further elevation by 1. Miller SL, Gladstone JN, Cleeman E, et al. Anatomy of the occupying the subcoracoid space. posterior rotator interval: implications for cuff mobilisa- tion. Clin Orthop 2003;408:152e6. Mengiardi et al. described a coracohumeral 2. Jost B, Koch PP, Gerber C. Anatomy and functional aspects ligament thickness greater than 4 mm on sagittal of the rotator interval. J Shoulder Elbow Surg 2000;9: oblique MR arthrographic images as a specific 336e41. sign of adhesive capsulitis.25 MRI may also show 3. Bennett WF. Technical note: visualisation of the anatomy of thickening of the rotator interval capsule and exu- the rotator interval and bicipital sheath. Arthroscopy 2001; 17:107e11. berant synovitis surrounding the coracohumeral 4. Clark J, Sidles JA, Matsen FA. The relationship of the gleno- ligament, which may enhance after intravenous humeral joint capsule to the rotator cuff. Clin Orthop 1990; gadolinium injection (Fig. 14).26 254:29e34. 5. Agur AMR. Grant’s Atlas of Anatomy. Baltimore: Williams and Wilkins; 1992. 6. Ho CP. MR imaging of the rotator interval, long biceps and associated injuries in the overhead-throwing athlete. Magn Reson Imaging Clin N Am 1999;7:23e37. 7. Chung CB, Dwek JR, Cho GJ, et al. Rotator cuff interval: evaluation with MR imaging and MR arthrography of the shoulder in 32 cadavers. J Comput Assist Tomogr 2000;24: 738e43. 8. Seeger LL, Lubowitz J, Thomas BJ. Tear of the rotator interval. Skeletal Radiol 1993;22:615e17. 9. Nidecker A, Guckel C, von Hochstetter A. Imaging the long head of biceps tendonda pictorial essay emphasizing magnetic resonance. Eur J Radiol 1997;25:177e87. 10. Cervilla V, Schweitzer ME, Ho C, et al. Medial dislocation of the biceps brachii tendon: appearance at MR imaging. Radiology 1991;180:523e6. 11. Bennett WF. Subscapularis, medial and lateral head coracohumeral ligament insertion anatomy: arthroscopic anatomy and incidence of ‘‘hidden’’ rotator interval lesions. Arthro- scopy 2001;17:173e80. 12. Weishaupt D, Zanetti M, Tanner A, et al. Lesions of the reflection pulley of the long biceps tendon. MR arthrographic findings. Invest Radiol 1999;34:463e9. 13. Murthi AM, Vosburgh CL, Neviaser TJ. The incidence of pathologic changes of the long head of the biceps tendon. J Shoulder Elbow Surg 2000;9:382e5. 14. Beall DP, Williamson EE, Ly JQ, et al. Association of biceps tendon tears with rotator cuff abnormalities: degree of correlation with tears of the anterior and superior portions of the rotator cuff. AJR Am J Roentgenol 2003; Figure 14 Sagittal oblique T1W fast spin-echo MR image 180:633e9. demonstrating enhancing soft-tissue (arrowheads) sur- 15. Gerber C, Sebesta A. Impingement of the deep surface of rounding the coracohumeral ligament (straight arrow), the subscapularis tendon and the reflection pulley on the extending towards the intra-articular portion of long anterosuperior glenoid rim: a preliminary report. J Shoulder head of biceps tendon (curved arrow). Elbow Surg 2000;9:483e90. MRI of the rotator interval of the shoulder 423

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