Multibody dynamics modeling of human mandibular musculoskeletal system and its applications in surgical planning

Many patients suffering from oral and maxillofacial tumors cannot open their mouths wide after mandibular reconstruction surgery. Musculoskeletal multibody modeling could be a valuable tool for predicting patient-specific jaw opening functions in the preoperative stage. In this study, a flexible multibody dynamics modeling framework of the human mandibular musculoskeletal system is proposed for surgical planning. In the model, the mandibular muscle bundles are discretized by a flexible cable element combining a typical Hill-type musculotendon model with distributed mass. The mandibular kinematics, together with the electromyographic activities of masticatory muscles, were measured in a patient with a unilateral mandibular tumor. Using the obtained experimental data, a forward–inverse dynamics procedure was proposed to realize the decoupled calculation of synergistic head movement and temporomandibular joint (TMJ) dynamics. The surgical planning simulation was driven by the measured activation patterns of the masticatory muscles and the calculated patterns of the jaw opening and pterygoid muscles. The muscle biomechanical parameters in the postoperative model were changed according to the medical imaging measurement of five patients before and after surgical interventions. As validation of the proposed surgical planning method, the predicted maximum jaw gape and mandibular deviations were compared with postoperative measurements. Numerical results further revealed the bistable characteristic of the TMJs together with the alternations of mandibular movement functions caused by muscle-release surgery. The proposed multibody simulation framework provides a novel method for understanding patient-specific pathology of suffering from trismus and assisting in designing treatments and rehabilitation strategies.