Wednesday, March 2, 2016

Rotator interval closure - an important surgical consideration in shoulder arthroplasty

Biomechanical effects of rotator interval closure in shoulder arthroplasty.

Out of interest in minimizing the risk of subscapularis dysfunction after shoulder arthroplasty, these authors explored the ability of a single rotator interval closing suture to off-load the subscapularis repair site in matched cadaveric shoulders having a subscapularis tenotomy and shoulder arthroplasty. The subscapularis tenotomy was repaired, and motion at physiologic torsional force was recorded. One of each matched pair was randomly assigned to receive an additional rotator interval closure suture. Each specimen then underwent standardized cyclic loading with measurement of gap formation and load to failure.

The rotator interval closing suture significantly increased the ultimate load to failure of the subscapularis repair and decreased gap formation at the subscapularis repair site. Measurement of the shoulder motion showed no significant difference between shoulders with and without the rotator interval closing suture.

Comment: While this paper speaks to rotator interval closure as a means of reinforcing the subscapularis repair, it is a much more powerful tool.

We have demonstrated the role of the superior aspect of the shoulder capsule, the coracoacromial ligament and rotator interval in shoulder stability. By holding the inseritional tendons to this anchoring point, translation of the humeral head (HH) with elevation of the arm is controlled. When this mechanism is deficient, a rotator interval plication can restore this function. We have found that rotator interval plication is a powerful tool for managing excessive posterior translation in shoulder arthroplasty.

As posted here and here, the degree to which the rotator interval is closed has a substantial effect on glenohumeral stability. This was pointed out decades ago in an important paper by our late partner, Douglas T Harryman II:

The role of the rotator interval capsule in passive motion and stability of the shoulder.
"The purpose of this study was to characterize the role of the capsule in the interval between the supraspinatus and subscapularis tendons with respect to glenohumeral motion, translation, and stability. We used a six-degrees-of-freedom position-sensor and a six-degrees-of-freedom force and torque-transducer to determine the glenohumoral rotations and translations that resulted from applied loads in eight cadaver shoulders. The range of motion of each specimen was measured with the capsule in the rotator interval in a normal state, after the capsule had been sectioned, and after it had been imbricated. Operative alteration of this capsular interval was found to affect flexion, extension, external rotation, and adduction of the humerus with respect to the scapula. Modification of this portion of the capsule also affected obligate anterior translation of the humeral head on the glenoid during flexion. Limitation of motion and obligate translation were increased by operative imbrication and diminished by sectioning of the rotator interval capsule. Passive stability of the glenohumeral joint was evaluated with the use of anterior, posterior, and inferior stress tests. Instability and occasional frank dislocation of the glenohumeral joint occurred inferiorly and posteriorly after section of the rotator interval capsule. Imbrication of this part of the capsule increased the resistance to inferior and posterior translation."

The application of this method as an adjunct for optimizing shoulder stability is shown here and here.


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