Rotator Cuff Interval

The rotator cuff interval (RI) is a triangular area formed by the interposition of three key components: the coracoid process, the subscapularis tendon, and the supraspinatus tendon.

The Rotator Cuff Interval borders are as following:

1. The medial base of the triangle is located at the coracoid process.
2. The anterior margin of the supraspinatus and the superior margin of the subscapularis make up the superior and inferior borders of the rotator interval triangle, respectively.
3. The lateral apex of the rotator interval is composed of the transverse humeral ligament which covers the bicipital groove and contributes to the bicipital sheath.

The contents of the Rotator Interval include:

1. the long head of the biceps tendon, the superior glenohumeral ligament (SGHL),
2. the coracohumeral ligament (CHL),
3. the glenohumeral joint capsule.

Jost et al. performed one of the more detailed cadaveric studies in which the rotator cuff interval was described as being composed of several layers. However, the precise anatomy of the rotator interval is still under investigation and is beyond the scope of this chapter.

Rotator Cuff Interval Function

The exact function of the rotator interval is also the subject of numerous biomechanical studies. However, many of their reported results have been conflicting.

Harryman et al. performed one of the first comprehensive and descriptive studies that examined the function of the structures within the rotator interval. After dividing the capsule and ligamentous structures within the rotator interval in a series of 80 cadaveric shoulders, the investigators noted an increase in passive glenohumeral flexion, extension, external rotation, and adduction capacity. Medial–lateral imbrication of the same structures resulted in the opposite effect, thus decreasing these motions. The authors concluded that the rotator cuff interval provided resistance against excessive motion while also functioning to limit posteroinferior glenohumeral translation.

Nobuhara and Ikeda also showed that tightening of the rotator interval decreased the propensity for humeral head translation in the posteroinferior direction.

As a result of these studies, most surgeons believe that the rotator cuff interval does provide some degree of stability, especially inferiorly when the humerus is externally rotated.

The rotator interval also contributes to stability of the LHB tendon as it travels through the bicipital groove towards the superior labrum and supraglenoid tubercle. Specifically, the SGHL, CHL, and subscapularis tendon together form a structure known as the biceps reflection pulley which supports the tendon as it enters the glenohumeral joint.

See Also: Long Head of Biceps Tendon

Rotator Interval Lesions

Due to the significant anatomic variability inherent to the rotator cuff interval, it is sometimes difficult to determine whether a physical finding is normal or abnormal. However, laxity of the rotator cuff interval can be detected on physical examination by inducing a sulcus sign of >2 cm when the humerus is externally rotated.

References

1. Jost B, Koch PP, Gerber C. Anatomy and functional aspects of the rotator interval. J Shoulder Elbow Surg. 2000;9(4):336–41.
2. Tamborrini G, Möller I, Bong D, Miguel M, Marx C, Müller AM, Müller-Gerbl M. The Rotator Interval – A Link Between Anatomy and Ultrasound. Ultrasound Int Open. 2017 Jun;3(3):E107-E116. doi: 10.1055/s-0043-110473. Epub 2017 Aug 23. PMID: 28845477; PMCID: PMC5568533.
3. Arai R, Mochizuki T, Yamaguchi K, Sugaya H, Kobayashi M, Nakamura T, Akita K. Functional anatomy of the superior glenohumeral and coracohumeral ligaments and the subscapularis tendon in view of stabilization of the long head of the biceps tendon. J Shoulder Elbow Surg. 2010;19(1):58–64.
4. Arai R, Nimura A, Yamaguchi K, Yoshimura H, Sugaya H, Saji T, Matsuda S, Akita K. The anatomy of the coracohumeral ligament and its relation to the subscapularis muscle. J Shoulder Elbow Surg. 2014;23(10):1575–81.
5. Nobuhara K, Ikeda H. Rotator interval lesion. Clin Orthop Relat Res. 1987;223:44–50.
6. Gambill ML, Mologne TS, Provencher MT. Dislocation of the long head of the biceps tendon with intact subscapularis and supraspinatus tendons. J Shoulder Elbow Surg. 2006;15(6):e20–2.
7. Walch G, Edwards TB, Boulahia A, Nove-Josserand L, Neyton L, Szabo I. Arthroscopic tenotomy of the long head of the biceps in the treatment of rotator cuff tears: clinical and radiographic results of 307 cases. J Shoulder Elbow Surg. 2005;14(3):238–46.