Since Neer described the rotator interval in 1970, its closure, often used in conjunction with capsulorrhaphy, has become an important surgical technique in managing shoulder instability.1-11 Numerous studies have sought to define the function of the rotator interval.1-3,6-20 The etiology of lesions of the rotator interval has been debated, and there is evidence that such lesions may be in part congenital.21 Increased rotator interval depth and width, along with increased size of the distended inferior and posteroinferior joint capsule on magnetic resonance arthrography, have been reported in cases of multidirectional shoulder instability.22 However, confusion remains about the role of the rotator interval in shoulder instability and about the effect its closure has on shoulder function. No one knows the degree of volume reduction that results from closure of the rotator interval and whether medial and lateral sutures differ in the volume reduction achieved.
Cadaveric studies have shown that the rotator interval has an important role in shoulder motion.6,13-16,19,20,23 Harryman and colleagues13 found that sectioning the coracohumeral ligament (CHL) increased shoulder range of motion (ROM), and medial-to-lateral closure of the rotator interval restricted motion in all planes. Most notably, interval closure limited inferior translation in the adducted shoulder, posterior translation in the flexed adducted shoulder, and external rotation in the neutral position. Subsequent studies,17,18 using rotator interval closure combined with thermal capsulorrhaphy, confirmed the results reported by Harryman and colleagues.13
More recent cadaveric studies using superior-to-inferior rotator interval closures have shown a decrease in anterior translation but not posterior translation.14-16,19-21 A superior-to-inferior interval closure technique limited external rotation less than a medial-to-lateral closure did.13-16,19-21 The majority of arthroscopically described rotator interval closures involve a superior-to-inferior technique and use 2 or 3 sutures.1,3,9-11
Plausinis and colleagues15 examined the effects of an isolated medial, an isolated lateral, and a medial combined with a lateral closure of the rotator interval. They noted that all 3 methods limited anterior translation and motion by means of 6° flexion and 10° external rotation; however, there was no statistical difference between methods. They also found that occasionally the medial interval closure resulted in massive loss of external rotation. Earlier, Jost and colleagues14 noted that a medial rotator interval could cause this massive loss by tethering the CHL, resulting in a medial-to-lateral imbrication of the CHL.
Arthroscopic rotator interval closure has clinically demonstrated an additive effect on shoulder stability. The recurrence rate was lower for arthroscopic Bankart repair combined with arthroscopic rotator interval closure (8%) than for arthroscopic Bankart repair alone (13%).24 In addition, time to recurrent dislocation was longer (42 vs 13 months) for the group that underwent the combination of Bankart repair and rotator interval closure. Regarding the concern about loss of motion after arthroscopic rotator interval closure, Chiang and colleagues25 recently noted no significant loss of motion 5 years after arthroscopic Bankart repair with rotator interval closure.
What effect rotator interval closure has on intra-articular glenohumeral volume (GHV) remains unknown. Using a cadaveric model, Yamamoto and colleagues20 showed that decreasing GHV can increase the responsiveness of the glenohumeral joint to the intra-articular pressure. Thus, reducing the volume can improve stability in vitro by increasing the magnitude of negative pressure stabilizing the glenohumeral joint.
We conducted a study to quantify the effects of arthroscopic rotator interval closure on capsular volume and to determine whether medial and lateral interval closures resulted in different degrees of volume reduction. Our hypothesis was that shoulder volume would be significantly reduced by closing the rotator interval.
Materials and Methods
Previous studies have not specifically evaluated GHV after rotator interval closure. Our power analysis was performed with data from a study by Karas and colleagues,26 who evaluated GHV after capsular plication. To detect a capsular volume reduction of 20% per stitch, with a 2-sided 5% significance level and a power of 80%, we needed a sample size of 5 specimens per group.
After receiving institutional review board approval for this study, we obtained 10 cadaveric shoulders (5 matched pairs). Exclusion criteria included arthroscopic evaluation revealing a full-thickness rotator cuff tear or significant osteoarthritis. Two shoulders had full-thickness cuff tears, leaving 8 shoulders to be tested; 6 of these were matched pairs. The shoulders were from 1 man (matched pair) and 4 women (2 matched pairs). Age ranged from 38 to 70 years (mean, 59.6 years). Differences in material properties between the specimens were accounted for by using primarily matched pairs.
The 2 study groups consisted of 4 shoulders each. After specimens were thawed, the skin, subcutaneous tissues, and periscapular muscles were removed from the shoulder. Only the capsule, biceps, and rotator cuff remained. For measurement purposes, the shoulders were mounted in a vice clamp in a beach-chair orientation. We placed a total of 2 portals with fully threaded 8.25-mm cannulas (Arthrex, Naples, Florida). A standard posterior portal was placed in the soft spot. A low anterior portal was then placed just superior to the subscapularis tendon. For arthroscopic examination and instrumentation in a saline environment, the shoulders were rotated into the lateral decubitus position, with suspension in 30° abduction and 20° forward flexion, by a rope attached to a pin in the distal shaft of the humerus.