The Rotator Interval and Long Head Biceps Tendon: Anatomy, Function, Pathology, and Magnetic Resonance Imaging

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Anatomy

The rotator interval is an anatomically defined triangular area located between the coracoid process, the superior aspect of the subscapularis (SSC), and the anterior aspect of the supraspinatus (SST), with the coracoid process at the base and the bicipital groove at the apex (Fig. 1). The interval is bridged by the glenohumeral capsule, which is composed histologically of loose connective tissue in which there are thick bands of collagen fibers that form the coracohumeral ligament (CHL),

Function of the Rotator Interval

The role of the rotator interval as a passive stabilizer of the glenohumeral joint has been a topic of long-standing research in numerous in vivo and in vitro studies. The CHL was found to be one of the factors preventing downward dislocation of the glenohumeral joint in electromyographic and cadaveric studies.7, 42 An extensive cadaveric study of the rotator interval by Harryman and colleagues43 revealed that sectioning of the rotator interval capsule and ligaments increased passive

MR imaging of the rotator interval and long head biceps tendon

MR imaging is the current imaging modality of choice in assessing the rotator interval and intra-articular LHBT (Box 1).55, 56, 57, 58 The standard MR protocol in the authors’ institution for a 1.5-T scanner includes an axial intermediate weighted sequence (retention time [TR] 2500–3000, echo time [TE] 34) with fat saturation, sagittal and coronal oblique T2-weighted sequences (TR 3000–4000, TE 42) with fat saturation, and a sagittal oblique T1-weighted sequence (TR400-650, TE 10). The MR

Rotator interval pathology

The spectrum of pathological conditions associated with the rotator interval varies between glenohumeral instability and adhesive capsulitis, indicating the delicate balance existing between structures occupying this space. In addition to lesions of the rotator interval capsule and ligaments, rotator interval abnormalities also include lesions involving the anterior aspect of the SST tendon and the superior aspect of the SSC tendon, as well as LHBT and long head biceps pulley lesions. Lesions

Long head biceps tendon pathology

The LHBT has been shown to slide up to 18 mm in and out of the glenohumeral joint during forward flexion and internal rotation, and turns 30° to 40° as it exits the joint and thus is subjected to mechanical stress in the groove, at the pulley, and by rotator cuff abnormality.33, 105 These mechanical stresses coupled with a netlike pattern of sensory and sympathetic innervation of the LHBT, concentrated at the biceps tendon anchor, may explain why the LHBT is well recognized as a pain generator

Diagnosis and imaging of long head biceps tendon lesions and instability

LHBT lesions or LHBT instability may be a difficult clinical diagnosis, as the symptoms are often nonspecific and include snapping, weakness, and anterior shoulder pain. On physical examination, LHBT pain is typically elicited by palpation over the bicipital groove or through provocation by performing a Speed or Yergason test.65, 107 A presumptive diagnosis of biceps tendon abnormality based on clinical examination is not infrequently made despite a lack of noticeable abnormality on arthroscopy.

Summary

The rotator interval and LHBT have become the focus of much research and discussion as their role in shoulder dysfunction is revealed and optimal treatment options are debated. The role of diagnostic imaging, such as MR imaging, in the context of rotator interval lesions has grown accordingly, in an attempt to provide anatomic detail that may go undetected on clinical evaluation and arthroscopy. Rotator interval and LHBT lesions may be subtle on MR imaging, and require comprehension of rotator

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      On short axis imaging, the lateral aspect of the coracohumeral ligament is seen as a hyperechoic linear structure extending from the subscapularis to the supraspinatus (see Fig. 1C). The mechanism of injury is believed to occur during horizontal adduction and internal rotation where the subscapularis tendon and biceps pulley impinge on the anterosuperior glenoid rim.56–61 Injury to these structures can be associated with microinstability.62,63

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      It is represented by a triangle; the base (medially) is the coracoid process and the apex (laterally) is at the transverse humeral ligament, forming the roof of the bicipital groove. The sides of the triangle are formed anteriorly by the capsule and CHL, and superiorly and inferiorly by the SST and SSC tendons.20,79,85,104 The contents of the RI are the anterior capsule, CHL, SGHL, MGHL, and the LHBT, which crosses the RI toward the bicipital groove.20,79,85,104,105

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