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Abstract & Commentary
Synopsis: A unique, anatomic study combined both fetal and adult cadaveric shoulder specimen dissections to evaluate the gross, radiographic, and histologic make-up of the rotator interval. Two types were identified, with the majority of specimens showing a complete defect (28 of 37 fetal specimens, 6 of 8 cadaveric) covered only by a thin layer of synovium, suggesting that the rotator interval defect is congenital.
Source: Cole BJ, et al. The anatomy and histology of the rotator interval capsule of the shoulder. Clin Orthop. 2001;390:129-137.
This study by Cole and colleagues from the Hospital for Special Surgery evaluated the anatomic findings of the normal rotator interval in fetal and cadaveric specimens. Cole et al note much confusion exists among shoulder specialists concerning this region defined as "a medially-based triangular space bordered superiorly by the anterior margin of the supraspinatus tendon, inferiorly by the superior border of the subscapularis tendon, medially by the base of the coracoid, and laterally by the long head of the biceps tendon and sulcus. The floor of the rotator interval region is variably bridged by capsule, the coraco humeral ligament, and occasionally, the middle glenohumeral ligament." The purpose of the study was to further describe this anatomic area both developmentally as well as in the adult shoulder with a multidisciplinary evaluation method.
Forty-seven shoulders from 37 fetuses were studied under institutional review board approval and involved gestation ages from 9 to 40 weeks. Analyzing the fetal specimens greater than 14 weeks gestation (n = 37), 2 types of intervals were noted: Type I (9 of 37) rotator intervals were defined by a contiguous bridge of capsule consisting of poorly organized collagen fibers; Type II rotator intervals (28 of 37) had a complete defect covered by only a thin layer of synovium. Eight cadaveric specimens were suitable for study and were arthroscopically evaluated with the rotator interval marked with a suture just medial to the biceps tendon. These specimens then underwent MRI, ultrasonographic, and gross/histologic evaluation. Six of the 8 adult cadaveric specimens were noted to have a complete defect with synovial covering similar to the Type II intervals seen in the fetal specimens. Cole et al concluded that the rotator interval is congenital and suggest that any surgical procedure involving closure of the rotator interval depend upon more substantial tissue adjacent to the interval.
Comment by Robert C. Schenck, Jr., MD
This ingenious study looked at gross, histologic, and radiographic (MRI and ultrasonography) findings of the anatomic appearance of the rotator interval in fetal and adult human cadaveric specimens, and it complements the many anatomic studies performed at this institution.1,2 Recent clinical work has focused on repair or closure of the rotator interval, especially in the presence of a sulcus sign with the arm adducted to the patient’s side. Furthermore, several investigators have noted failure of surgical reconstructions for shoulder instability because of failure to address a rotator interval lesion. Several techniques of arthroscopic or open rotator interval closure have been presented, and Cole et al provide useful anatomic information to aid in our understanding of this area. Because this area was determined to be congenitally made up of thin tissue, any surgical technique involving a repair of the rotator interval should include substantial tissue immediately adjacent to the rotator interval.
1. Fealy S, et al. The developmental anatomy of the neonatal glenohumeral joint. J Shoulder Elbow Surg. 2000;9:217-222.
2. O’Brien SJ, et al. The anatomy and histology of the inferior glenohumeral ligament complex of the shoulder. Am J Sports Med. 1990;18:449-456.