In Silico Modeling of Safe Force Limits for Trismus Therapy Following Jaw Reconstruction

Restricted mouth opening (trismus) is a common complication following segmental mandibulectomy and autologous bone reconstruction. However, the biomechanical limits of reconstructed mandibles, particularly in cases without bone union, remain poorly understood. Restorabite is a novel jaw-stretching device designed to increase the safety of trismus therapy by controlling the applied force. This study estimates the patient-specific loading limits in compromised mandibular reconstruction using finite element analysis to guide safe trismus therapy.

Based on patient imaging, the finite element method was used to model stress distributions in the bone, titanium plate, and screws of a reconstructed mandible lacking bone union. Various scenarios were simulated to determine safe loading parameters, which considered factors such as friction coefficients between bone segments, native bone, and the reconstructed plate, as well as force application sites, and concentrated versus distributed loading.

Low friction coefficients significantly increased stress on the reconstruction plate. To simulate the worst-case scenario, a coefficient of 0.3 was applied in the subsequent simulations. Stress levels varied by loading sites, with concentrated loading on the posterior segment of grafted bone yielding the lowest stress. In contrast, distributed loading over the 4 cm region on the anterior segments of graft bone led to increased plate stress.

This study highlights the importance of tailored approaches in trismus therapy to minimize osteolysis and plate failure in mandibular reconstruction providing valuable insights for future clinical practices and device development. The study found that concentrated loading on biomechanically favorable regions proved safer compared to distributed loading, as it occurs with traditional jaw-stretching devices.