The Anatomic Variability of the Rotator Interval Capsule: A Comparison of Arthroscopic and Open Surgical Techniques (SS‐15) (2006)

To define the rotator interval (RI) from both open and arthroscopic approaches, compare their dimensions, and compare arthroscopic and open techniques of suture passage for closure of the RI. Twelve fresh cadaveric shoulders were randomized between arthroscopic and open RI closure methods. For the open group, the optimal site of suture placement was first marked arthroscopically on both the superior and middle glenohumeral ligaments (SGHL and MGHL). Sutures were then placed in open fashion. Two coordinate planes were oriented along the SGHL and MGHL and their respective origins centered on the optimal arthroscopic sites previously marked. Distance of the suture from the origin and its location in one of four superimposed quadrants defined by the coordinate planes were noted. For the arthroscopic group, these steps were reversed. The length of the superior border of the SGHL and that of the superior edge of the subscapularis between the SGHL and MGHL were measured both arthroscopically and open. The subscapularis measurements were performed in neutral, maximal internal, and maximal external rotation. The maximum opening of the capsule from outside and the maximum arthroscopic distance from the lateral insertion of the SGHL to the inferior opening of the capsule along the MGHL were determined. Sutures placed arthroscopically through the SGHL always captured the coracohumeral ligament (CHL) in the superolateral quadrant and averaged 15.0 mm (SD=10.8 mm) from the marked optimal location. Sutures placed open through the SGHL never engaged the CHL and exited in the superomedial quadrant with a mean distance from the optimal location of 8.3 mm (SD=5.4 mm). Arthroscopic MGHL sutures exited 5.5 mm (SD=4.0 mm) and open MGHL sutures exited 6.4 mm (SD=7.2 mm) from the optimal locations in multiple quadrants. The arthroscopic inferior border of the RI extended more inferiorly than the superior border of the subscapularis in all specimens. Five of 12 specimens had an additional foramen between the MGHL and anterior band of the IGHL (aIGHL) that, from an open approach, was similar in appearance to the interval between the SGHL and MGHL. The RI capsule tends to decrease in medial to lateral width with internal rotation. Arthroscopically placed sutures in the SGHL always capture the CHL, which may cause more loss of external rotation in arthroscopic RI closures than in similar open procedures. There was less variation between MGHL sutures placed arthroscopically and open. The inferior border of the RI capsular defect does not correspond to the classically described superior border of the subscapularis tendon and actually extends more inferiorly. The presence of two intervals (between the SGHL and the MGHL and between the MGHL and the aIGHL) in several specimens points to the existence of anatomic variability that may drastically affect surgical outcomes should the inappropriate interval be closed. RI closure surgery performed from an open approach is not equivalent to that performed arthroscopically and more study of the two techniques is warranted.