In both groups, medial and lateral stitches with No. 2 FiberWire (Arthrex) were used to close the interval. The medial interval closure stitch was placed more than 10 mm away from the glenoid to prevent unpredictable CHL tethering; the lateral closure stitch was placed 10 mm lateral to the medial stitch (Figure 1).14 All sutures were placed intra-articularly under direct arthroscopic visualization, similar to the methods described in the literature.1,3,9-11 Sutures were passed through the superior glenohumeral ligament (SGHL) and through the upper subscapularis using a suture shuttle (SutureLasso; Arthrex) and Penetrator II Suture Retriever (Arthrex). The upper subscapularis was incorporated because of the unpredictable nature of the middle glenohumeral ligament (MGHL). Both rotator interval sutures were placed before tying either. In the medial group, the medial stitch was tied first, using alternating half-hitches, followed by the lateral stitch. In the lateral group, the lateral stitch was tied first, followed by the medial stitch. GHV was measured at baseline and after tying each stitch. Dr. Ponce instrumented all shoulders.
Modifying a beach-chair technique described by Miller and colleagues,27 we used a viscous fatty-acid sulfate solution, liquid soap, to measure GHV.27-29 A small slit in line with the fibers was made in the supraspinatus tendon just lateral to the musculotendinous junction. A 3-way stop-cock was placed into the joint though this defect. A 20-mL syringe with a 16-gauge needle was used to inject the soap. The needle was inserted into the rotator cuff interval, and the viscous solution was injected in 5-mL increments until there was active extravasation through the supraspinatus cannula (Figure 2). This technique, the “volcano method,” marked the maximum capacity of the joint. The joint was then copiously irrigated with normal saline and suctioned until all normal saline was evacuated. Dr. Rosenzweig took 2 measurements on each shoulder, and their mean was used for analysis.
The baseline measurement was taken with the 2 working cannulas in the shoulder joint. Measurements were obtained with cannulas to simulate normal clinical conditions. Subsequent measurements were done with the cannulas in place and inserted up to the same thread each time so as not to change the volume. The capsule and the rotator cuff were then dissected from the humerus so the size of the capsulolabral plication could be directly evaluated. Methylene blue was used to mark the capsular suture holes before removing the sutures. With use of a caliper, the size of the plication bite was measured (in millimeters).
Statistical Analysis
The primary outcome was percent reduction in GHV as a function of number of plications and size of plication. When only the first plication was tightened, the effect of position (medial or lateral) was also of interest. Percent volume reduction was calculated as (original – new) / original × 100. SAS 8.02 (SAS Institute, Cary, North Carolina) was used to fit a repeated random-intercept regression model for each outcome. This technique properly accounts for the paired nature of the specimens and the repeated measures (baseline plus 2 plications). Model fit was assessed by the method of difference in log likelihood.
Results
In the medial group, GHV was reduced by a mean of 24.2% with a single medial stitch; in the lateral group, GHV was reduced by a mean of 35.1% (Figure 3). The difference was significant (P < .02). In the medial group, when a second lateral stitch was used, GHV was reduced by another 18.7%; in the lateral group, when a medial stitch was added, GHV was reduced by another 11.4%. Final GHV for the medial and lateral groups was 42.9% and 46.5%, respectively. There was no statistical difference in final GHV, regardless of which stitch was placed first. When the 2 groups were combined, GHV was reduced by 44.9% with use of medial and lateral rotator interval closure stitches.
Mean amount of tissue purchased, or “bite size,” was 18 mm with a lateral suture and 15 mm with a medial suture (P < .05). In addition, an increase in bite size to GHV reduction was essentially linear, where an increase in bite size of 1 mm reduced GHV by about 1% (Figure 4).
Discussion
Although there have been numerous clinical series and biomechanical studies focused on isolated rotator interval closure (or its use as an adjunct) in shoulder stabilization, the precise function of the rotator interval remains poorly understood.1-3,6-11,19 Consequently, the in vivo effects of interval closure are unknown.