Prediction of human bone sawing forces from bone porosity, tool geometry, and machining parameters

Oscillating saws are widely used in orthopaedic surgery, where sawing forces contribute to thermal and mechanical bone damage. Although three parameters such as, bone porosity, machining parameters, and tool properties all influence sawing forces, their combined effects on human bone remain poorly understood. This study investigates the relationship between sawing forces and these three parameter groups. The porosity of four fresh-frozen human cadaveric femoral bone samples was examined under a digital microscope. Then, samples were sawn using a single-tooth of a commercial saw blade at approximately 0.4 m/s sawing speed. Cutting and thrust forces were measured during sawing while varying depth of cut (20, 40, and 60 μm), sawing orientation (across and transverse), and the saw-tooth rake angle. A multivariable regression model incorporating depth-of-cut, sawing orientation, saw-tooth rake angle, and cortical porosity explained 88.2% and 88.9% of the variation in cutting and thrust forces. Increasing DOC elevated sawing forces by approximately 71-132%, while sawing orientation and saw-tooth rake angle changed them by up to 38%. At a depth-of-cut of 20 μm, 29-43% of the cutting force and 53-78% of the thrust force removed no bone. Inverting the model gave the apparent shear strength of the bone, which fell by 24-32% as porosity rose from 3.2% to 25.7%. The dataset and the regression model presented in this study establish a foundation to support saw blade selection and design, as well as the setting of sawing machining parameters based on patient bone microstructure, with the aim of minimising sawing forces.