Optimal design of an individual endoprosthesis for the reconstruction of extensive mandibular defects with finite element analysis

AimThe aim of this study was to evaluate the finite element analysis (FEA) approach to assess biomechanical performance of individual endoprostheses used in the reconstruction of extensive mandibular defects, and to explore an available strategy for the optimal design of prostheses.Material and methodsA female patient experienced fracture of a titanium mandibular endoprosthesis one year after reconstructive surgery. The endoprosthesis was placed during resection of a mandibular carcinoma. Using CT data, a finite element analysis (FEA) of the implant was performed to identify potential causes for this mechanical failure. Based on the first FEA analysis, modifications of the prosthesis geometry and screw configuration were carried out. FEA was performed for each subsequent modification until no stress concentration areas were identified. The final version of the titanium prosthesis was implanted during the second mandibular reconstruction.ResultsThe FEA model was constructed, based on the geometrical data of the patient. Two areas of stress concentration were identified in the original prosthesis:- at the top surface of the left stem, 1.5 cm away from the corner (the peak stress was 616 MPa) and- on the exterior surface of the right stem, close to the mandibular stump margin.The mechanical failure occurred at the top surface of the left stem. Some common characteristics of the biomechanical performance were noted in the two models, but lower overall stress was achieved in the second, optimized prosthesis. By thickening the recognized high stress areas, and attenuating those areas subject to less stress, then adopting a quadrilateral screw configuration, this dispersed the stress more evenly in the optimized endoprosthesis. Function in the optimized reconstructed mandible was observed for 3 years without significant endoprosthesis related complication.ConclusionIn some patients with extensive mandibular defects, the individually tailored endoprosthesis constructed with regard to minimizing stress concentration using this method seems to have a place. The prosthesis geometry and screw configuration influence the stress–strain distribution on the reconstructed mandible. Our FEA approach can optimize the design of individual endoprostheses and give the reconstructed mandible improved biomechanical performance.