Minimum Distance of Suture Anchors Used for Rotator Cuff Repair Without Decreasing the Pullout Strength: A Biomechanical Study.

Abstract

PURPOSE: To investigate the minimum distance between the anchors without decreasing the pullout strength using the polyurethane foams and the porcine bones. METHODS: Metal screw-type anchors and PEEK (polyether ether ketone) coil-type anchors were used. Two same-type suture anchors were placed into the polyurethane foams and porcine bones. The polyurethane foams were 3 different densities simulating severe osteoporosis, osteoporosis, and normal bone. The distances between the centers of anchors were set at 4, 6, 8, and 10&#xa0;mm. The pair of anchors were loaded to failure if they had not been pulled out after cyclic loading from 50 to 200&#xa0;N, 10 cycles per each 50-N increment. Mode of failure, ultimate load to failure, displacement of the anchor, and number of cycles completed were recorded. RESULTS: In all polyurethane foams of 3 different densities with use of metal screw-type anchors, the 4-mm group demonstrated a significantly lower ultimate load to failure compared with the 6-, 8-, and 10-mm groups (P < .01). There were no significant differences in the load to failure among the 6-, 8-, and 10-mm groups. Porcine bone or PEEK coil-type anchor showed results similar to those of the metal screw-type anchors. CONCLUSION: For the 2 tested anchors, the minimum distance between the anchors without decreasing the pullout strength was 6&#xa0;mm (center to center) regardless of bone density in a biomechanical study. CLINICAL RELEVANCE: Although it has been thought that the minimum distance between the anchors without decreasing the pullout strength was 1&#xa0;cm (center to center), our data showed that it was 6&#xa0;mm.