Citation: ALAM, K., MITROFANOV, A.V. and SILBERSCHMIDT, V.V., 2010.Experimental investigations of forces and torque in conventional and AbstractBone drilling is widely used in orthopaedics and surgery; it is a technically demanding surgical procedure. Recent technological improvements in this area are focused on efforts to reduce forces in bone drilling. This study focuses on forces and a torque required for conventional and ultrasonically-assisted tool penetration into fresh bovine cortical bone.Drilling tests were performed with two drilling techniques, and the influence of drilling speed, feed rate and parameters of ultrasonic vibration on the forces and torque was studied.Ultrasonically-assisted drilling (UAD) was found to reduce a drilling thrust force and torque compared to conventional drilling (CD). The mechanism behind lower levels of forces and torque was explored using high-speed filming of a drill-bone interaction zone and was linked to the chip shape and character of its formation. It is expected that UAD will produce holes with minimal effort and avoid unnecessary damage and accompanying pain during the incision.

Bone fractures affect the health of many people and have a significant social and economic effect. Often, bones fracture due to impacts, sudden falls or trauma. In order to numerically model the fracture of a cortical bone tissue caused by an impact it is important to know parameters characterising its viscoelastoplastic behaviour. These parameters should be measured for various orientations in a bone tissue to assess bone's anisotropy linked to its microstructure. So, the first part of this study was focused on quantification of elastic-plastic behaviour of cortical bone using specimens cut along different directions with regard to the bone axis -longitudinal (axial) and transverse. Due to pronounced non-linearity of the elastic-plastic behaviour of the tissue, cyclic loadingunloading uniaxial tension tests were performed to obtain the magnitudes of elastic moduli not only from the initial loading part of the cycle but also from its unloading part.Additional tests were performed with different deformation rates to study the bone's strain-rate sensitivity. The second part of this study covered creep and relaxation properties of cortical bone for two directions and four different anatomical positionsanterior, posterior, medial and lateral -to study variability of bone's properties. Since viscoelastoplasticity of cortical bone affects its damping properties due to energy dissipation, the Dynamic Mechanical Analysis (DMA) technique was used in the last part of our study to obtain magnitudes of storage and loss moduli for various frequencies.Based on analysis of elastic-plastic behaviour of the bovine cortical bone tissue, it was found that magnitudes of the longitudinal Young's modulusfor four cortical positions were in the range of 15-24 GPa, while the transversal modulus is lower -between 10-15 GPa. Axial strength for various anatomical positions was also higher than transversal one with a significant differences in magnitudes for those positions.. Quantitative data obtained in creep and relaxation tests exhibited no significant position-specicifc differences.. DMA results demonstrated relatively low energy loss capability due to viscosity of bovine cortical bone that has a loss factor in the range of 0.035-0.1.

Bone cutting is an essential part of orthopaedic surgery when bone is fractured or damaged by a disease and is used for pins insertion and plates fixation. A finite element model of bone cutting is developed and compared with experimental results. The model allows the interaction between the bone and cutting tool to be studied, hence enabling the evaluation and optimization of the cutting procedure. Results of finite element simulations are obtained for the cutting force as a function of cutting parameters. A strong dependence of cutting parameters on the cutting force was found and described in this paper.

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