BIOMECHANICAL EFFECT OF MEDIAL ADVANCEMENT OF THE SUPRASPINATUS TENDON - A STUDY IN CADAVERA

During the repair of some rotator-cuff tears, the torn tendon cannot b e heed up adequately to permit reattachment at its original anatomical site of insertion. An option is to advance the site of insertion medi ally and reattach the tendon to a trough in the sulcus or to the humer al head, The biomechanical effects of such medial advancement on the m oment arm of the supraspinatus muscle during glenohumeral elevation we re studied in ten fresh-frozen shoulders from cadavera, Medial advance ment of the site of insertion of the supraspinatus tendon was simulate d by the placement of suture anchors in the sulcus of the proximal par t of the humerus at points three, ten, and seventeen millimeters media l to the junction of the supraspinatus tendon and the bone. These dist ances were chosen not because they represent clinical options but beca use the large range allowed biomechanical study of medial advancement. Nylon lines were attached to the suture anchors and were passed back through an eyehook at the midpoint of the supraspinatus muscle. The ex cursion of each line was measured as the humerus was elevated, and the moment arm was estimated from the joint angle and excursion data with use of the principle of virtual work, Three and ten millimeters of me dial advancement of the tendon (attachment in the sulcus) had a minimu m (nonsignificant) effect on the moment arm during elevation compared with the value determined for the intact condition. However, seventeen millimeters of medial advancement was found to reduce the moment arm significantly (p < 0.05). CLINICAL RELEVANCE: Our study of cadavera in dicates that a limited amount of medial advancement las much as ten mi llimeters) is acceptable from a biomechanical point of view although t he clinical maximum is dictated by other clinical factors.