Evaluation of Internal Fixation Techniques for Extracapsular Fracture: A Finite Element Analysis and Comparison

•This FE analysis improves the simulation of the TMJ disc•Double plates and bi-cortical screws fixation of ECF increases stability•L-shape plate exhibits no significant difference with straight plate in fixation•Plate breakage and bone microcrack might happen on single plate fixation This study explored the optimal plates and screws fixation for extracapsular fracture by finite element analysis, and provided a biomechanical basis for clinical treatment. Four extracapsular fixation models were built and evaluated: A. One single straight four-hole plate with two bi-cortical screws on both sides and two mono-cortical screws in the middle; B. One single straight four-hole plate with four bi-cortical screws; C. Two straight four-hole plates, each with two bi-cortical screws on both sides and two mono-cortical screws in the middle; D. One L-shape four-hole plate in the back and one straight four-hole plate in the front, each with two bi-cortical screws on both sides and two mono-cortical screws in the middle. Displacements of fractured bone blocks and stress of plates, screws, cortical and cancellous bone and the deformation of plates were analyzed by finite element analysis to investigate their stability in clinical using. Groups A and B showed larger displacements of the fractured bone block, greater deformation of plates and higher risk of the plate breakage during masticatory motion. Groups C and D exhibited the minimum displacements of the fractured bone block, the stress distribution within the safe range and less deformation of the plates. In addition, double plates fixation and bi-cortical screws exceeded single plate fixation and mono-cortical screws in stability, respectively, while an L-shape plate exhibited no significant differences in the stress dispersion and the displacement reduction. Double plates fixation of the extracapsular condylar fracture was a safe and stable way and bi-cortical screws should be selected as far as possible.