Passive contribution of the rotator cuff to abduction and joint stability.

PURPOSE: The purpose of this study is to compare shoulder joint biomechanics during abduction with and without intact non-functioning rotator cuff tissue.

METHODS

A cadaver model was devised to simulate the clinical findings seen in patients with a massive cuff tear. Eight full upper limb shoulder specimens were studied. Initially, the rotator cuff tendons were left intact, representing a non-functional rotator cuff, as seen in suprascapular nerve paralysis or in cuff repair with a patch. Subsequently, a massive rotator cuff tear was re-created. Three-dimensional kinematics and force requirements for shoulder abduction were analyzed for each condition using ten abduction cycles in the plane of the scapula.

RESULTS

Mediolateral displacements of the glenohumeral rotation center (GHRC) during abduction with an intact non-functioning cuff were minimal, but massive cuff tear resulted in significant lateral displacement of the GHRC (p < 0.013). Similarly, massive cuff tear caused increased superior migration of the GHRC during abduction compared with intact non-functional cuff (p < 0.01). From 5 to 30° of abduction, force requirements were significantly less with an intact non-functioning cuff than with massive cuff tear (p < 0.009).

CONCLUSION

During abduction, an intact but non-functioning rotator cuff resulted in decreased GHRC displacement in two axes as well as lowered the force requirement for abduction from 5 to 30° as compared with the results following a massive rotator cuff tear. This provides insight into the potential biomechanical effect of repairing massive rotator cuff tears with a biological or synthetic "patch," which is a new treatment for massive cuff tear.