Subject-Specific Finite Element Modelling of Le Fort I Osteotomy Fixation: Biomechanical Insights Comparing Patient-Specific Implants and Conventional Miniplates

Background: Stable fixation is essential to prevent relapse after Le Fort I osteotomy, particularly during the early postoperative period when the fixation system bears the full masticatory load. Patient-specific implants (PSI) have been increasingly used, but their biomechanical behavior under postoperative surgical conditions remains insufficiently investigated. The aim of this study was to evaluate PSI fixation using subject-specific finite element modelling based on real surgical plans. Methods: Two patient-specific models were developed from cone-beam computed tomography (CBCT) data of patients undergoing bimaxillary orthognathic surgery. For each case, two fixation strategies were simulated: a multiarm patient-specific plate and conventional L-shaped miniplates. Von Mises stress distribution and relative displacement were analyzed for fixation devices and bone segments. Results: PSI fixation reduced stress levels in plates and screws while maintaining comparable global stability. However, its effect on bone stress differed between the two models. In Patient 2, whose surgical plan included greater maxillary advancement and posterior impaction, PSI fixation was associated with higher bone stress and a micrometric increase in displacement. Conclusions: These findings highlight the influence of surgical movement on fixation biomechanics and support the integration of biomechanical personalization alongside anatomical planning in orthognathic surgery.