Anatomical, histological and radiological study of the rotator cuff interval of the shoulder

ABSTRACT

The Rotator cuff interval [RCI] is the triangular capsular space between the insertion of tendons of supraspinatus and subscapularis muscles. This RCI is supposed to be reinforced superficially by the coracohumeral ligament and deeply by the superior glenohumeral ligament SGHL. In addition to the ligamentous structures, the participation of the supraspinatus and subscapularis muscles tendons in the composition of the RCI has been pointed out. The aim of the present work was to study RCI, its boundaries and components, macroscopically and microscopically in correlation to MRI. Fourteen adult human cadaveric shoulder regions [5 right and 9 left] obtained from the Anatomy Department, Faculty of Medicine, Ain Shams University, were used in the present study. Specimens with gross pathology, trauma or previous surgery were excluded. Retrospectively the normal MRI findings were examined in 19 volunteers [10 right and 9 left shoulders, after obtaining consents] to demonstrate the boundaries and contents of the RCI using 1.5 tesla [General Electric Medical System [Milwaukee]. Results gross dissection at the apex of RCI revealed extension of fibers from subscapularis and supraspinatus tendons across the location of the RCI. They merge together in this region forming a confluence of fibers amalgamating with the capsule from outside. The long bicipital tendon was supported anteriorly by the suspension sling formed by the SGHL which seems to stabilize the long head of biceps in the RCI. The subscapularis tendon and the middle glenohumeral [GH] ligament, supported the antero-medial wall of the RCI. Sections taken from the lateral part of the roof, near the apex of the RCI and the superomedial part showed three distinct layers of connective tissue bundles. In sections taken in close proximity to the tendinous insertions into the tuberosities showed a zone of fibrocartilage. Sections from antero-medial part of the roof of RCI showed a meshwork of loose connective tissue. The RCI is best demonstrated in sagittal cuts. However, coronal and axial cuts can be helpful in identification of the relationship and contents. The coracohumeral [CHL] is always well identified in the mid portion of the RCI and is visualized in all planes, but sagittal images are the most useful for analysis of this structure. In conclusion studying the anatomy of RCI and determining [RCI] at MR imaging is important as it will provide a scientific background to the surgeon to repair any interval tear to stabilize the shoulder and may explain to some extent the superior instability observed in shoulders with rotator cuff tears