The Effect of Suture Anchor Insertion Angle on Calcaneus Pullout Strength: Challenging the Deadman’s Angle

Background. Refractory cases of Achilles tendinopathy amenable to surgery may include reattachment of the tendon using suture anchors. However, there is paucity of information describing the optimal insertion angle to maximize the tendon footprint and anchor stability in the calcaneus. The purpose of this investigation is to compare the fixation strength of suture anchors inserted at 90° and 45° (the Deadman’s angle) relative to the primary compressive trabeculae of the calcaneus. Methods. A total of 12 matched pairs of adult cadaveric calcanei were excised and potted to approximate their alignment in vivo. Each pair was implanted with 5.5-mm bioabsorbable suture anchors placed either perpendicular (90°) or oblique (45°) to the primary compressive trabeculae. A tensile load was applied until failure of anchor fixation. Differences in failure load and stiffness between anchor fixation angles were determined by paired t-tests. Results. No significant differences were detected between perpendicular and oblique suture anchor insertion relative to primary compressive trabeculae in terms of load to failure or stiffness. Conclusion. This investigation suggests that the fixation strength of suture anchors inserted perpendicular to the primary compression trabeculae and at the Deadman’s angle are possibly comparable. Levels of Evidence: Biomechanical comparison study