Biomechanical Study: Determining the Optimum Insertion Angle for Screw‐In Suture Anchors—Is Deadman's Angle Correct?

Purpose To assess the effect of the insertion angle and the angle of applied load on the pullout strength of screw‐in suture anchors. Methods Screw‐in metallic suture anchors were inserted into a 10–lb/cu ft synthetic cancellous bone block at 30°, 45°, 60°, and 90° to the surface. The suture pull angle was then varied in 30° increments between 0° and 180°. Five constructs were tested to failure (anchor pullout) for each combination of angles using a Zwick tensile testing machine (Zwick Roell, Ulm, Germany). Results There were a total of 25 combinations. The greatest pullout strength was seen with a suture anchor inserted at 90° to the bone block with a pull angle of 90° to the bone (mean, 306 N; standard deviation [SD], 9 N). The weakest pullout strength was seen with a suture anchor inserted at 30° with the angle of pull at 120° (i.e., opposite to the direction of insertion of the anchor) (mean, 97 N; SD, 11 N). A simulated deadman's angle of 45° with an angle of pull of 150° produced a pullout strength of 127 N (SD, 4 N). The pullout strengths for each insertion angle were greatest when the angle of pull was similar to the angle of insertion ( P < .0001, repeated‐measures analysis of variance). Conclusions The angle of applied load to a suture anchor and the insertion angle significantly influence the biomechanical pullout strength of screw‐in suture anchors. The insertion angle of the suture anchor should replicate the angle of applied load to ensure the optimum pullout strength. Clinical Relevance The screw‐in anchor insertion angle and angle of applied load may have an influence on pullout strength.