Bone anchors or interference screws? A biomechanical evaluation for autograft ankle stabilization

Background: Autograft stabilization uses free semitendinosus tendon grafts to anatomically reconstruct the anterior talofibular ligament. Study aims were to evaluate the biomechanical properties of Mitek GII anchors compared with the Arthrex BioTenodesis Screw for free tendon reconstruction of the anterior talofibular ligament. Hypothesis: There are no differences in load to failure and percentage specimen elongation at failure between the 2 methods. Study Design: Controlled laboratory study using porcine models. Methods: Sixty porcine tendon constructs were failure tested. Re-creating the pull of the anterior talofibular ligament, loads were applied at 70degrees to the bones. Thirty-six tendons were fixed to porcine tali and tested using a single pull to failure; 10 were secured with anchors and No. 2 Ethibond, 10 with anchors and FiberWire, 10 with screws and Fiberwire, and 6 with partially gripped screws. Cyclic preloading was conducted on 6 tendons fixed by anchors and on 6 tendons fixed by screws before failure testing. Two groups of 6 components fixed to the fibula were also tested. Results: The talus single-pull anchor group produced a mean load of 114 N and elongation of 37% at failure. The talus single-pull screw group produced a mean load of 227 N and elongation of 22% at failure (P < .05). Cyclic preloading at 65% failure load before failure testing produced increases in load and decreases in elongation at failure. Partially gripped screws produced a load of 133 N and elongation of 30% at failure. The fibula model produced significant increases in load to failure for both. The human anterior talofibular ligament has loads of 139 N at failure with instability occurring at 20% elongation. Conclusions: Interference screw fixation produced significantly greater failure strength and less elongation at failure than bone anchors. Clinical Relevance: The improved biomechanics of interference screws suggests that these may be more suited to in vivo reconstruction of the anterior talofibular ligament than are bone anchors.