A multi-directional fracture stiffness model to determine the principal stiffness properties of a healing human tibia

A model for the stiffness of a fractured human tibia has been developed. The model is based on Mohr’s circle of inertia and relies on tibial fracture stiffness being measured in a number of planes. Using in vitro data, it has been shown that this model can be used to identify the principal stiffness values and their associated planes. It has also been shown that only 4/5 independent measurements are required to generate good correlation between experimental data and fitted data. Initial in vivo experiments show that this model transfers from the laboratory to clinical practice. The model illustrated that the maximum plane for a complete tibia is about 12°–14° relative to anterior–posterior, which correlates with previous publications. It is postulated that the model can be used for further in vitro studies to confirm the most common angle of the minimum stiffness plane. The knowledge of this angle may help orthopaedic surgeons to better assess fracture stiffness and may be the starting point for further discussion about the current minimum value of 15 N m/°.