The effect of the angle of suture anchor insertion on fixation failure at the tendon-suture interface after rotator cuff repair: deadman's angle revisited.

PURPOSE To evaluate what effect the angle of screw-in suture anchor insertion has on fixation stability at the suture-tendon interface. METHODS Supraspinatus tendons from 7 matched pairs of human cadaveric shoulders were split, yielding 4 tendons per cadaver. An experimental rotator cuff tear was created and repaired, using a 5.0-mm diameter screw-in suture anchor. In a staggered, matched pair arrangement, the angle of anchor insertion was varied between 45 degrees (deadman's angle) and 90 degrees to the articular surface. Each repair underwent cyclic loading, and 2 failure points were defined: the first at 3 mm of repair site gap formation and the second at the point of complete failure. The number of cycles to failure was compared between the 2 groups. RESULTS The mean number of cycles to 3-mm gap formation for anchors inserted at 90 degrees was 380. This was significantly higher than for repairs made with the 45 degrees angle of anchor insertion (mean, 297 cycles). Complete failure occurred at a significantly greater number of cycles with the 90 degrees anchors (mean, 443 cycles) compared with the 45 degrees anchors (mean, 334 cycles). CONCLUSIONS Compared with anchors placed at the current standard of the deadman's angle of 45 degrees, suture anchors placed at 90 degrees to the junction of the greater tuberosity and the humeral head articular surface provided improved soft tissue fixation in an experimental rotator cuff model. CLINICAL RELEVANCE The angle of suture anchor insertion into the greater tuberosity during rotator cuff repair has an effect on the soft tissue fixation at the tendon-suture interface.