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.