Finite-Element Syntheses of Callus and Bone Remodeling: Biomechanical Study of Fracture Healing in Long Bones.

Computational simulations of fracture healing are a valuable tool to improve fracture treatment and implants. Several finite-element models have been established to predict callus formation due to mechanobiological rules. This work provides a comprehensive simulation for virtual implantation through the combination of callus simulation and finite-element structural synthesis (FESS) of (re-)modeling during and after healing based on Pauwel's theory of histogenesis and Wolff's law. The simulation is based on a linear elastic material model and includes generation of fracture hematoma and initial mesenchymal stem cell concentration out of an unspecified solid, cell proliferation, migration, and differentiation due to mechanical stimuli and time-dependent axial loading. Three nondisplaced femoral shaft fractures with initial interfragmentary movement of 0.2, 0.6, and 1 mm and one fracture with 4 mm translation are modeled. The predictions of interfragmentary movement during fracture healing, healing success, and healing time agree with observed clinical outcome, animal models, and other numerical models. Initial interfragmentary movement between 0.2 and 1 mm leads to healing success, with the fastest healing occurring at 0.2 mm. The model of the dislocated fractures shows no further bending after remodeling and is loaded with physiological stress of -13 MPa. Ideal load-time graphs may give insight into the bone's ability to withstand loads as healing time progresses, and thus holds potential for applications in rehabilitation planning. Better knowledge of the forces present during fracture healing is needed to deploy simulations for surgical planning and manufacturing of patient individualized implants. Anat Rec, 301:2112-2121, 2018. © 2018 Wiley Periodicals, Inc.