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

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 mm. The pair of anchors were loaded to failure if they had not been pulled out after cyclic loading from 50 to 200 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 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 cm (center to center), our data showed that it was 6 mm.