The Role of Physiological Loading on Bone Fracture Healing Under Ilizarov Circular Fixator: The Effects of Load Duration and Loading Frequency

Abstract

One of the main advantages of Ilizarov Circular Fixator (ICF) is that it enables early weight bearing, which is beneficial for patients’ mobility. In addition, it is believed that early weight bearing could lead to faster and stronger fracture callus development and thus, enhance healing progression. Therefore, it is important that the early weight bearing exercises (e.g. walking) are carefully designed for the best possible conditions within the fracture site during the crucial early stage of healing. In this study, using a computational model, we explored the influence of (i) duration and (ii) frequency of dynamic loading under ICF (resulting from early weight bearing exercises), on the early fracture microenvironment. The model simulated the interactions and transport of bone cells (i.e. mesenchymal stem cells, osteoblasts, chondrocytes and fibroblasts) and growth factors (i.e. osteogenic growth factor and chondrogenic growth factor) within the early callus under dynamic loading. The changes in cell and growth factor concentrations due to different load durations (1–4 h) and load frequencies (1–4 times/day) were parametrically studied. The results suggest that continuous dynamic loading and longer durations (e.g. 4 h in a stretch) are preferable over shorter durations (e.g. 1 h) and intermittent loading for chondrogenic differentiation, which is beneficial for secondary healing. The results also suggested that, intermittent loading of longer total durations (e.g. 4 times [× 1 h]) could be more beneficial in the later stages for osteogenesis.