The Rotator Interval - A Link Between Anatomy and Ultrasound

Abstract

Shoulder pathologies of the rotator cuff of the shoulder are common in clinical practice. The focus of this pictorial essay is to discuss the anatomical details of the rotator interval of the shoulder, correlate the anatomy with normal ultrasound images and present selected pathologies. We focus on the imaging of the rotator interval that is actually the anterosuperior aspect of the glenohumeral joint capsule that is reinforced externally by the coracohumeral ligament, internally by the superior glenohumeral ligament and capsular fibers which blend together and insert medially and laterally to the bicipital groove. In this article we demonstrate the capability of high-resolution musculoskeletal ultrasound to visualize the detailed anatomy of the rotator interval. MSUS has a higher spatial resolution than other imaging techniques and the ability to examine these structures dynamically and to utilize the probe for precise anatomic localization of the patient's pain by sono-palpation.

Keywords: interval; rotator cuff; shoulder.

Conflict of interest statement

Conflict of Interest The authors declare that they have no conflict of interest.

Figures

Fig. 1

Drawings of the rotator interval. Superior glenohumeral ligament (SGHL), middle glenohumeral ligament (MGHL), anterior inferior glenohumeral ligament (IGHL), coracohumeral ligament (CHL), medial coracohumeral ligament (MCHL), Lateral coracohumeral ligament (LCHL), subscapularis tendon (SSC), long biceps tendon (LBT) and supraspinatus tendon (SSP).

Fig. 2

Anatomical section through the rotator interval showing the superior glenohumeral ligament (SGHL), the medial (MCHL) and lateral (LCHL) coracohumeral ligament (CHL), the long biceps tendon (LBT), the supraspinatus tendon (SSP) and the subscapularis tendon (SSC).

Fig. 3

Arthroscopic image showing the long biceps tendon (LBT), the superior glenohumeral ligament (SGHL) and the lateral bundle of the coracohumeral ligament (LCHL).

Fig. 4

Histological image (toluidine blue) of the rotator interval showing the long biceps tendon (LBT), the superior glenohumeral ligament (SGHL) and the lateral (LCHL) and medial (MCHL) coracohumeral ligament (CHL).

Fig. 5

Patient in supine position, arm in neutral position:a; arm in retroversion:b; arm in retroversion and slightly external rotation:c; patient in a sitting position. Arm in neutral position:d; in external rotation and abduction:e; in the modified Crass position:f.

Fig. 6

Transverse oblique ultrasound image of the rotator interval in a modified Crass position demonstrating an anisotropy effect (box) of the long biceps tendon (LBT), of the superior glenohumeral ligament (SGHL) and of the medial (MCHL) and lateral (LCHL) coracohumeral ligament (CHL), subscapularis tendon (SSC), supraspinatus tendon (SSP).

Fig. 7

Longitudinal oblique ultrasound image of the origin of the long biceps tendon (asterisks) in a modified Crass position with forced internal rotation.

Fig. 8

Transverse oblique ultrasound image of the rotator interval in a relaxed neutral position with flexed elbow and supinated forearm demonstrating an anisotropy effect (box at the bottom) of the long biceps tendon (LBT) and of the superior glenohumeral ligament (SGHL), subscapularis tendon (SSC), supraspinatus tendon (SSP) and of the medial (MCHL) and lateral (LCHL) coracohumeral ligament (CHL).

Fig. 9

Anatomical section anterior oblique showing the coracoacromial ligament (asterisks) and the coracohumeral ligament (plus signs) in an external rotation and retroversion position, coracoid process (c), acromion (a).

Fig. 10

Ultrasound images of the rotator interval in a transverse view (at the top) and longitudinal oblique view (at the bottom) in a modified Crass position. Superior glenohumeral ligament (SGHL), lateral coracohumeral ligament (LCHL), long biceps tendon (LBT), supraspinatus tendon (SSP).

Fig. 11

Arthroscopy of the rotator cable and ultrasound image of the supraspinatus tendon longitudinal in a modified Crass position: peribursal structures (b), layer I=superficial layer, measuring 1 mm in thickness and composed of fibers from the coracohumeral ligament (LCHL) which extends posteriorly and obliquely, infraspinatus and supraspinatus tendon layer (ISP and SSP, respectively) composed of 3 layers: layer II=densely packed fibers of the tendon, 3–5 mm in thickness, layer III=3 mm thick and composed of smaller bundles of collagen which are loosely organized at an approximately 45 degree angle to the long axis of the tendon, layer IV=loose connective tissue and thick collagen bands and merges with fibers from the coracohumeral ligament), layer V (LCHL/capsule)=capsule and glenohumeral ligament, 2 mm in thickness, cartilage (c). Note the anisotropy effect at the insertion due to the different trajectories of the different layers. Anisotropy artifacts typically affect the insertional area at the level of the footprint of the humeral head. To avoid these artifacts, try to tilt the probe laterally to have the ultrasound beam as perpendicular as possible to the tendon or the ligament fibers.

Fig. 12

Adhesive capsulitis phase 1. Transverseaand longitudinal obliquebpower Doppler images in a modified Crass position obtained over the rotator cuff interval. Images show the normal long head of the biceps tendon (asterisks) that appears thin and hyperechoic. The tendon is surrounded by a hypervascular area related to inflammation of the rotator cuff interval.

Fig. 13

Adhesive capsulitis phase 2. Transverseaand longitudinal obliquebimages obtained over the anterior aspect of the shoulder in a relaxed neutral position with flexed elbow and supinated forearm. Images show the coracohumeral ligament (black arrowheads) that is thickened and hypoechoic. The normal coracoacromial ligament is thin and hyperechoic (white arrowheads).

Fig. 14

Tear of the supraspinatus and posterior bundle of the coracohumeral ligament (CHL). Transverseaand longitudinal obliquecimages in a modified Crass position and corresponding MR images obtained over the anterior aspect of the shoulder. Images show medial subluxation of the long head of the biceps tendon (black arrowheads) due to tear on the anterior CHL bundle and supraspinatus (black arrows). The anterior bundle of the CHL and the glenohumeral ligament (white arrows) are continuous and retain the tendon to dislocate completely.

Fig. 15

Tear of the subscapularis tendon associated with a partial tear of the anterior sling. Longitudinalaand transverseboblique images obtained respectively over the rotator cuff interval and anterior aspect of the shoulder. Ina, note the irregularly thickened anterior sling (black arrowheads) suggesting a partial tear. The long head of the biceps tendon (asterisk) and the supraspinatus tendon (white arrows) are normal. Note the absence of instability of the long head of the biceps tendon. An anechoic fluid collection (Eff) is located close to the subscapularis tendon (small black arrow) which appears thin and hypoechoic. Inb, a complete tear of the subscapularis tendon is evident (calipers). Note the larger retracted tendon stump (large arrow) and the smaller distal stump (small arrow).

Fig. 16

Tear of the subscapularis tendon associated with a complete tear of the anterior sling. Transverseaand longitudinal obliquecimages obtained at the anterior face of the shoulder. Longitudinal obliqueeimage obtained over the supraspinatus tendon. Corresponding MR imagesb,d,f). Ina,b, note the complete tear of the subscapularis tendon (black arrow) associated with the intraarticular dislocation of the long head of the biceps (white arrows). The white arrowheads point to the empty biceps groove. Inc,d, longitudinal US and MRI images show the tear of the anterior sling (black arrowheads). Ine,f, the supraspinatus tendon is normal.