The effect of human bone morphology on sawing forces

In orthopaedic surgical procedures, bone cutting is often performed with an oscillating saw. Achieving an optimal cut requires high accuracy, low temperature, minimal surgeon effort, and time efficiency, all of which may be influenced by the forces applied on the sawing device, and the microstructure of the cut bone. The relation between bovine bone microstructure and sawing forces has been studied. However, transition to human bone remains limited. This study investigates the relationship between human bone microstructure and sawing forces. Transverse cross-sections of seven fresh-frozen human cadaveric femoral bone samples were obtained and their porosity and osteon density were captured by a microscope. Samples were sawed in four quadrants using a single-tooth saw blade in a dedicated test setup at 0.39 ± 0.01 m/s, while forces on the tooth were measured. Subsequently, the relationship between porosity and osteon density with cutting and thrust forces was analysed by regression analysis for each one/third of the sawing area. Microstructure analysis of the sawed areas showed a porosity varying between 5 and 86 % and an osteon density between 1 and 31 osteons/mm². A logarithmic regression model revealed a significant relationship between these properties and cutting forces (1.58-16.37 N) and thrust forces (1.94-14.19 N), explaining 68 % of the variance of the applied forces on the saw tooth. The proposed regression model adequately predicts sawing forces depending on human bone porosity. Hence, this study introduces a methodology and data set which can serve as a first step towards optimizing machining parameters of saw blades in orthopaedic bone sawing.