INFLUENCE OF BONE DENSITY OF THE HUMERAL GREATER TUBEROSITY ON THE MECHANICAL STRENGTH OF BONE ANCHORS FOR ROTATOR CUFF REPAIR

Abstract

Aim: The aim of the study was to investigate the influence of bone density of the greater tuberosity on mechanical strength of different bone anchors for rotator cuff surgery. Especially in osteopenic bone the metal bone anchors and transosseus sutures are still the “gold-standard” in rotator cuff surgery.

Material and Methods: Four bone anchors, each standing for a specific group of bone anchor, and two suture materials were tested. One of them was the metallic Super Revo screw 5.0 (Linvatec), the absorbable screw Spiralok 5.0 (Mitek), the absorbable press-fit anchor Bioknotless RC (Mitek) and the absorbable Ultrasorb RC (Linvatec). The suture materials tested was the well known V-37 (Ethicon) and the new Orthocord (Mitek) both USP 2. All fixations systems were tested on a) 6 pairs of fresh-frozen human shoulders from young adults (range 20–50 yrs.) and b) 6 pairs of fresh frozen human shoulders from elderly (range 60–93 yrs.). Cyclic loading was performed, as it was considered the best way to simulate the postoperative conditions in a manner similar to those used in prior studies until the system failed. The maximum tensile strength, the failure mode, and the displacement of the fixation device (system displacement) under load at the first cycle at 75 N and at the maximum tensile strength were recorded.

Results: The absorbable Spiralok 5 mm screw anchor showed the highest failure load with a mean of 171 N in osteopenic bone. The suture material Orthocord and V-37 had the lowest mechanical strength in osteopenic bone with a mean of 125 N resp. 114 N. The remaining anchors had an almost identical failure load with means of 150 N (Super Revo 5 mm and Bioknotless RC) and 151 N (Ultrasorb RC). No statistical significance was found though. Comparing the mechanical strength of each fixation system in healthy and osteopenic bone no statistical significant difference was found except for the V-37 suture. In healthy bone the failure load of V-37 suture had a mean of 204 N and in osteopenic bone of 114 N.

Discussion: The absorbable Spiralok 5 mm screw showed a good performance in healthy and osteopenic bone when compared with standard bone anchor like the titan Super Revo 5 mm screw or transosseous sutures. Absorbable anchors have certain advantages, besides that usually they are more expensive. They can easily be overdrilled in case of rupture of the suture material, and they do not interfere during later revision surgery or for imaging studies such as magnetic resonance imaging.