Pullout Strength of All-Suture Anchors: Effect of the Insertion and Traction Angle—A Biomechanical Study

Purpose To evaluate the pullout strength of the all-suture anchor (ASA), based on the angles of anchor insertion and traction. Methods Synthetic saw bones of 2 densities (0.16 and 0.32 g/cm 3 ) with 3 mm thick cortical bone models were used. ASAs were inserted at 45°, 60°, 75°, or 90° and pulled at 2 angles from the surface: 45° (simulating the physiological pull of the supraspinatus) and 90° (simulating pulling out during knot tying). Five consecutive pullout tests for each insertion and traction angle combination per saw bone were conducted to evaluate the ultimate load to failure and mode of failure (80 tests total). Thereafter, 9 matched pairs of human cadaveric humeri with 2 ASA types were used (insertion angles, 45°, 75°, 90°; traction angle, 90°). Nine consecutive tests were conducted for each insertion angle and anchor type (54 tests total). Results The pullout strength was significantly higher for high density- than for low-density saw bones (all P P P P > .05). Conclusions ASA showed stronger pullout strength in higher density bones. Furthermore, it presented stronger pullout strength in the physiological traction direction of supraspinatus rather than in the knot-tying direction, consistent with the deadman theory. However, stronger pullout strength was observed in the vertically directed insertion angle, not 45°. Therefore, implanting the ASA vertically may be clinically more beneficial not only when performing knot tying during surgery, but also when the supraspinatus tendon loads the ASA postoperatively. Clinical Relevance The study provides biomechanical evidence that the optimal insertion angle for an ASA is more vertical than the 45°.