One of the recently introduced anchors is the absorbable suture anchor BIOKNOTLESS-RC, a press-fit anchor whose special feature is the knotless reconstruction of the ruptured rotator cuff. We compared the new knotless anchor BIOKNOTLESS-RC with established anchors.

The absorbable pressfit anchor BIOKNOTLESS-RC (DePuyMitek, Raynham, MA, USA), the titanium screw anchor SUPER-REVO 5mm and the tilting anchor ULTRASORB (both ConmedLinvatec, Largo, FL, USA) were tested 12 times in the greater tuberosity of human cadaveric humeri (mean age: 74 years). They were inserted according to the manufacturers instructions with the supplied suture material. An incremental cyclic loading was performed, starting with 75N. Until failure the tensile load was increased by 25N after every 50 cycles. The ultimate failure loads, the anchor displacements and the modes of failure were recorded.

The anchor displacement of the BIOKNOTLESS-RC (15.3mm) after the first cycle with 75N was significantly higher than with the two others (SUPER-REVO 2.1mm, ULTRASORB: 2.7mm). The ultimate failure loads of the tested anchors were comparable: BIOKNOTLESS-RC 150N, SUPER-REVO 150N, ULTRASORB 151N (p> 0,05).

Rupture of the suture material at the eyelet occurred more frequently with the SUPER-REVO. BIOKNOTLESS-RC and ULTRASORB showed a tendency towards anchor pullout.

Our results do not confirm the higher pullout strength of metal anchors, which was found in other studies. Knotless anchors facilitate surgery by eliminating the technically challenging step of arthroscopic knot tying. The disadvantage of the BIOKNOTLESS-RC is its unsatisfactory primary stability. Its initial displacement of a mean of 15.3 mm is clinically significant and jeopardizes the rotator cuff repair.

Because of the high initial displacement and the possible gap formation between tendon and bone, the use of the BIOKNOTLESS-RC in a zone of minor tension, for instance as a second-row anchor in double row technique only is recommend.

Absorbable suture anchors have become more and more important in rotator cuff surgery due to their easy revisability. In osteoporotic bone however they are thought to be of minor primary stability. Purpose of the present study was to compare different absorbable and non-absorbable suture anchors in their pullout strength depending on bone density

The absorbable screw-anchor SPIRALOK5mm (DePuyMitek, Raynham, MA, USA), the titanium screw-anchor SUPER-REVO5mm and the tilting-anchor ULTRASORB (both ConmedLinvatec, Largo, FL, USA) were tested, each anchor representing a different material and design. On the basis of bone density measurement by CT-scans a healthy (mean-age. 42 years) and a osteopenic (mean-age: 74 years) group of cadaveric human humeri were formed. Each anchor was inserted in the greater tuberosity six times. They were inserted according to the manufacturers instructions with the supplied suture material. An incremental cyclic loading was performed, starting with 75N. Until failure the tensile load was increased by 25N after every 50 cycles. The ultimate failure loads, the anchor displacements and the modes of failure were recorded.

In the non-osteopenic bone group, the absorbable SPIRALOK achieved a significantly better pullout strength (mean: 274N) than the titanium screw-anchor SUPER-REVO (mean: 188N) and the tilting-anchor ULTRASORB (mean: 192N). In the osteopenic bone group no significant difference in the pullout strength was found. The failure mechanisms, such as anchor pullout, rupture at eyelet, suture breakage and breakage of eyelet, varied between the anchors. In the osteopenic group the number of anchor pullouts clearly increased.

The present study demonstrates that absorbable suture anchors do not have lower pullout strengths than metal anchors. Depending on their design they can even outmatch metal anchor systems. The results of our study suggest that the anchor design has a crucial influence on primary stability, whereas the anchor material is less important.

Aim: Retears after rotator cuff surgery occur frequently and may compromise the functional results. Failure of bone anchors and sutures may influence the results to a great part. The goals of this in vitro investigation were to determine the mechanical strength and stiffness of different bone anchors frequently used in arthroscopic rotator cuff surgery. Focus was put a material and design of the anchors.

Material und Methods: Four bone anchors were tested, each standing for a specific group of bone anchor. 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 Ultra-sorb RC (Linvatec). The anchors were tested on 12 pairs of fresh-frozen human shoulders. The mean age at the time of death was fifty-seven years (range 27–93 yrs.).

Cyclic loading was performed, as it was considered the best way to simulate the postoperative conditions. The maximum tensile strength, the failure mode, and the displacement of the fixation device (system displacement) under load at the first cycle of 75 N and at the maximum tensile strength were recorded.

Results: As reported before the most frequent failure mode for the titan anchor Super Revo 5 mm was a rupture of the threads at the eyelet.

The absorbable Spiralok 5 mm screw anchor showed the highest failure load with a mean of 223 N. The failure loads of the remaining anchors were similar and ranged from a mean of 169 N for the Super Revo 5 mm, over a mean of 173 N for the Ultrasorb RC anchor to a mean of 188 N for the Bioknotless anchor. Among these anchors the differences were not significant. Only the Spiralok 5 mm screw showed a significantly higher failure load when compared with the Super Revo 5 mm screw.

The displacement of the various systems showed significant differences. The displacement of the Bioknotless anchor showed after the cycle with a tensile strength of 75 N a mean displacement of 13.8 mm, which was significant when compared with the remaining anchors.

Discussion: Our study shows that there is no advantage in using titan anchors with regards to primary stability in arthroscopic rotator cuff repair. We could even detect a significantly higher failure load for the absorbable Spiralok 5 mm screw anchor compared to the Super Revo 5 mm titan screw. Stability and system displacement depend not only on the anchor material but on the design of the anchor. We found that the absorbable Bioknotless RC anchor showed a significantly higher system displacement during the first cyclic loading (75 N) while all other anchors tested had a similar system displacement.

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.