The Role of Far Cortical Endosteal Fixation for the Treatment of Medial Malleolus Fractures: A Biomechanical Study

Abstract

The traditional method for fixation of medial malleolus fractures has been with partially threaded (PT) lag screws extending beyond the physeal scar. The purpose of this study was to evaluate the biomechanical strength of an innovative method of fixation for medial malleolus fractures using a fully threaded (FT) lag screw that extends to the far endosteal cortex. Medial malleolus fractures were simulated in 12 matched cadaver pairs. A single PT 4.0-mm cancellous lag screw was placed in 1 ankle. The contralateral ankle of the same matched pair received an FT 3.5-mm cortical lag screw that extended to the far lateral tibial cortex and achieved endosteal purchase. Final torque of both screw configurations was recorded, and radiographs were taken to confirm appropriate screw placement. Average torque for the PT cancellous screws was 5.02 ± 2.34 in-lb. Average torque for the FT cortical screw was 7.63 ± 3.86 in-lb (p = .002). Visual and radiographic inspections revealed no displacement of the fracture site with use of the FT endosteal lag screw. Our results indicate superior biomechanical torque with far endosteal fixation with use of an FT cortical lag screw versus a traditional PT cancellous lag screw in a cadaver model. Far endosteal fixation is an alternative surgical option for medial malleolus fractures that provides added strength compared with PT lag screws and may obviate downsides associated with bicortical fixation.