An individualized simulation model based on continuous, independent, ground force measurements after intramedullary stabilization of a tibia fracture

The interfragmentary movement (IFM) is a key determinant for the fracture healing process. Different simulation models allow the prediction of the IFM in the fracture gap based on an estimated ground force. For this purpose, a workflow capable for implementation into the clinical routine workup was developed as a proof of concept based on individualized IFM simulations. Starting with clinical X-ray image data, a personalized computational model of the tibial shaft fracture and the intramedullary stabilization was set up in a computer-aided design system, assigned with material parameters, equipped with patient-specific boundary conditions and passed to finite element simulations. We obtained continuously measured postoperative patient gait data from a novel pedobarography insole, mapped the gait data onto an OpenSim gait model and used the resulting forces as input for the simulation of the IFM during a step forward and a step downstairs. In order to verify the simulation results with respect to the IFM, a series of different configurations for the bone material parameters are tested combined with different levels of mesh discretization. The results show IFM values comparable in range to simulation results based on validated OrthoLoad data for even surface gait as well as during walking downstairs. The computed shear movements in the coronal and the sagittal planes were low, and a complete fracture healing of the patient was observed after 6 months. The presented simulation-based workflow can determine the patients' weight-bearing specific interfragmentary movement after an intramedullary stabilization of a tibial shaft fracture.