Mechanoregulation modeling of bone healing in realistic fracture geometries.

In bone fracture healing, new tissue gradually forms, ossifies, and eventually remodels itself to restore mechanical stiffness and strength across injury site. Mechanical strain at the fracture site has been implicated in controlling the process of healing and numerical mechanoregulation models with strain-based fuzzy logic rules have been applied to simulate bone healing for simple fracture geometries. However, many of these simplified models cannot capture in vivo observations such as delays in healing with torsional instability or differences in healing rate between different fracture types. Accordingly, the purpose of this work was to apply a fuzzy logic mechanoregulation fracture healing simulation technique to 3D models representing a range of clinically inspired fracture geometries with intramedullary nail fixation and multiaxial loading conditions. The models predicted that the rate of healing depends on the geometry of the fracture and that all fracture types experience a small healing delay with torsional instability. The results also indicated that when realistic torsional loading and fixator mechanics are included, previously published strain-based rules for tissue destruction lead to simulated nonunions that would not be expected in vivo. This suggested that fracture healing may be more robust to distortional strain than has been previously reported and that fuzzy logic models may require parameter tuning to correctly capture clinically relevant healing. The strengths of this study are that it includes fracture morphology effects, realistic implant mechanics, and an exploratory adaptation of the upper distortional strain threshold. These findings may help future researchers extend these methods into clinical fracture healing prediction.