A biomechanical study on suture anchor insertion angle: Which is better, 90° or 45°?

Introduction The purpose of this study was to compare the pullout strength of anchors inserted at 90° and 45° to the bone surface using synthetic bones and porcine humeri. Subjects and methods Pullout tests were performed by universal testing machine. Synthetic cancellous bones of 0.08, 0.16, and 0.24 g/cm³ (defining as low, medium and high density, respectively) with 2-mm-thick cortical bone model attached on one side and the greater tuberosity of porcine humeri (average bone density, 270 mg/cm³) were chosen for pullout tests. Metallic anchors were inserted at 90° or 45° to the surface and pulled at 90° or 45° from the surface. The maximum load to failure for each condition was recorded. Differences in pullout failure loads between insertion angle, pulling angle, and bone density were analyzed. Results When the sutures were pulled at 90° in low, medium, high density bones, and porcine humeri, 90°-inserted-anchors showed higher pullout strength than the 45°-inserted-anchors (534.6 ± 28.9 N vs. 488.1 ± 25.3 N (p < 0.05), 636.8 ± 25.3 N vs. 517.5 ± 27.4 N (p < 0.01), 735.6 ± 45.1 N vs. 557.0 ± 42.5 N (p < 0.01), and 285.6 ± 47.2 N vs. 181.4 ± 31.3 N (p < 0.01), respectively). When the sutures were pulled at 45° in low, medium density bones and porcine humeri, 90°-inserted-anchors showed higher pullout strength than the 45°-inserted-anchors (651.1 ± 38.3 N vs. 529.4 ± 37.6 N (p < 0.01), 711.4 ± 25.3 N vs. 599.2 ± 29.8 N (p < 0.01), and 265.3 ± 49.0 N vs. 181.5 ± 29.4 N (p < 0.01), respectively). Conclusion Pullout strength of the anchors inserted at 90° to the bone surface was greater than the anchors inserted at 45° regardless of the bone density.