[Purpose] We performed a biomechanical comparison of the pullout strength of a suture anchor that we have been using for arthroscopic rotator cuff repair with a transosseous suture.
[Materials and methods] Four pairs of fresh-frozen cadaveric human shoulders were used. The average age was 75.8 years old. Each had an intact rotator cuff. The proximal part of the humerus was harvested and a bone trough was created on the greater tuberosity. Each one was tested three times using three sites of the trough. A screw anchor (Fastin RC, Mitek) with two No. 2 braided sutures was inserted at an angle of 45 degrees to the humeral axis. The humerus was fixed and sutures were distracted in direction of the humeral axis until an anchor pullout or suture breakage occurred (anchor group, n=12). Then, a bone tunnel was created through the greater tuberosity and doubled No.2 braided sutures were placed, and tested in a similar way (suture group, n=12).
[Results] The modes of failure were anchor pullout in ten and suture breakage in two of the anchor group, bone cutout in eight and suture breakage in four of the suture group. The average failure load of the anchor group was 211.3 N (SD=65.2) and that of the suture group was 208.7 N (SD=68.6). The average stiffness of anchor group was 48.33 KN/m (SD=15.97) and that of suture group was 28.78 KN/m (SD=16.47). There was no significant difference in the average failure load, but the average stiffness was significantly higher in the anchor group (p<0.01, unpaired t-test).
[Conclusions] Since the average stiffness was significantly higher in anchor group, the size of the gap at the tendon repair site during ROM exercises after suture anchor repair may be smaller than that after a transosseous suture repair. These findings are the background in the clinical use of the suture anchor for a rotator cuff repair.
