The Effects of Dynamic Loading on Bone Fracture Healing Under Ilizarov Circular Fixators

: Early weight bearing appears to enhance bone fracture healing under Ilizarov Circular Fixators (ICFs). However, the role of early weight bearing in the healing process remains unclear. This study aims to provide insight into the effects of early weight bearing on healing of bone fractures stabilized with ICFs, with the aid of mathematical modelling. A computational model of fracture site was developed using poroelastic formulation to simulate the transport of mesenchymal stem cells (MSCs), fibroblasts, chondrocytes, osteoblasts, osteogenic growth factor (OGF) and chondrogenic growth factor (CGF) and the mechanical loading mediated MSC differentiation during the early stage (i.e first day), under various combinations of fracture sizes, ICF configurations and loading conditions. The results show that, physiologically relevant cyclic loading could significantly enhance cell and growth factor concentrations in the fracture site in a time and spatially dependent manner. 1 hour cyclic loading (axial load with amplitude, PA, of 200 N at 1 Hz) increased the concentration of MSC up to 8% (cortical callus), chondrocytes up to 15 % (endosteal and cortical callus), osteoblasts up to 16 % (cortical callus), CGF up to 28% (endosteal and periosteal callus) and OGF up to 48 % (endosteal and cortical callus) on the first day, suggesting that the synergistic effect of dynamic loading induced advective transport and mechanical stimuli due to early weight bearing is likely to enhance healing. Furthermore, the study suggests that, relatively higher PA or lower ICF stiffness can increase cell and GF concentrations in callus.