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Introduction: Variably present rotator interval capsular openings (RICOs) complicate anterior shoulder capsular anatomy. Open and arthroscopic approaches may lead to differences in the appearance and size of RICOs. The purposes of this study are to: (1) Confirm that RICOs viewed from inside and outside the joint are the same structures, and (2) compare the size of RICOs when approached in an open manner vs arthroscopically. Materials and methods Twelve fresh cadaveric shoulders were randomized to two different approaches in order to identify and mark RICOs. In the first group, the superior glenohumeral ligament (SGHL) and middle glenohumeral ligament (MGHL) were marked arthroscopically. Sutures were placed in these structures in an open fashion. Repeat arthroscopy was then performed to determine whether the sutures penetrated the marked SGHL and MGHL. In the second group, these steps were reversed and arthroscopically placed sutures were evaluated in an open manner. Dimensions of the RICOs were measured both arthroscopically and open in each shoulder. Results All specimens had a RICO visualized both arthroscopically and open. Five of 12 specimens had an additional second RICO. RICO size measurements were similar for the arthroscopic and open techniques. Sutures placed via both the arthroscopic and open technique were noted to penetrate the marked structures in all cases. In addition, sutures placed through the SGHL while viewing arthroscopically always captured the coracohumeral ligament (CHL). Sutures placed through the SGHL with an open technique never engaged the CHL. Conclusion The capsular openings in the rotator interval were confirmed to be the same structures when observed arthroscopically and through an open approach. Svoboda SJ, Taylor DC, Magnussen RA. The Anatomic Variability of the ‘Rotator Interval Capsule’: A Comparison of Arthroscopic and Open Investigations. The Duke Orthop J 2013;3(1):54-60.