Drilling procedures are important to optimize and ensure the strongest fixation in bone fracture treatment and reconstruction surgery. The mechanistic force models currently available for bovine bones, human spines and human mandibles are not relevant to perform drilling through human femurs. The present study addresses this lack of information and aims to develop the predictive force models for drilling human femurs at different regions and directions. In this study, 10 freshly harvested cadaveric human femurs were included, and a surgical drill bit of 3.2[Formula: see text]mm diameter was used to make 4[Formula: see text]mm deep holes. Different spindle speeds (500, 1000 and 1500[Formula: see text]rpm), feed rates (40, 60 and 80[Formula: see text]mm/min), and apparent density between 0.98 and 1.98[Formula: see text]g/cm3were considered. The optimal parameters [Formula: see text], [Formula: see text], and [Formula: see text] respectively obtained for longitudinal, radial, and circumferential direction could minimize the thrust forces in bone drilling by up to 7.70, 10.50, and 16.20 N, respectively. Validation study demonstrated that the force model developed could predict the thrust force from computed tomography data sets of the patient, only with 5.05%, 6.74%, and 4.91% as a maximum error in longitudinal, radial, and circumferential direction. This important tool can assist to perform complicated surgical operations.

Constitutive models are widely used to predict the mechanical behavior of different kinds of materials. Although the Johnson–Cook model for bovine bone and Cowper–Symonds model for human thoracic rib and tibia was developed, the predictability of these models was found good only at particular strain rates. This study addresses this lack of information by investigating the Cowper–Symonds model, Johnson–Cook model, and Johnson–Cook model combined with Cowper–Symonds model at different strain rates to utilize in the bone cutting simulation. Specimens prepared using two rear femurs harvested from a 3.50-year-old bovine were investigated at different strain rates (0.00001–1/s). A comparative study made among the stresses predicted from these models showed 29.41%, 10.91%, and 11.11% mean absolute percentage errors using Cowper–Symonds model, and 2.03%, 7.19%, and 3.62% mean absolute percentage errors using Johnson–Cook model, respectively, at 0.0001, 0.001 and 1/s strain rates. However, the Johnson–Cook model combined with the Cowper–Symonds model predicted the stress with a maximum of only 2.03% mean absolute percentage error. The potential of each model to utilize in the orthogonal bone cutting was also evaluated using Ansys® and found that the combined model predicted the cutting force close to experimental cutting force with minimal error (5.20%). The outcomes of this study can be used in the surgical practice and osteotomy procedure before commencing actual surgery.

In orthopaedic surgeries, drilling through bone is most widely used to fix the plates and implants. The uncontrolled large thrust forces generated during bone drilling cause micro-crack, and fragmentation around the local host bone which further loosen the implant and fixation. Owing to the experimental limitation and the risk of infection in handling the bone specimens, conducting experiments with all possible combinations of parameter values and selecting the suitable combination is largely limited. So in this paper, finite element analysis coupled with the constitutive models was used to early predict the thrust forces generated in the surgical bone drilling process. The constitutive models developed in the earlier study, namely, Johnson–Cook, Cowper–Symonds, and Johnson–Cook combined with Cowper–Symonds that consider the strain rate dependence of plastic curve were used for the simulations. Results revealed that the trends of the thrust force values predicted from the constitutive models matched well with the experiments. However, the study showed that the Johnson–Cook model combined with the Cowper–Symonds model predicted the thrust forces with a maximum error of only 9.51% followed by the Johnson–Cook model and Cowper–Symonds model with 15.83% and 21.89%, respectively. The outcomes of the study can be used to predict the thrust forces generated in the bone drilling process, and thus, suitable parameters values can be selected to avoid the mechanical damages around the bone drilling site. The outcomes can also be used to plan and rehearse the in-silico bone drilling trials with any combinations of parameter values before performing the actual surgery.

Compression plates are widely used in orthopaedic surgeries for internal fixation of fractured femurs. To fix the plate and thus to provide compression to a fracture, the self-tapping bone screws are tightened through predrilled pilot holes of smaller diameter. Preliminary investigation showed that the holes drilled with the inappropriate cutting parameters cause mechanical and thermal damages to the local host bone, which further lead to loosening of internal fixations. In this paper, the mechanistic models to predict the thrust forces and torques during bone drilling were developed, using a 3.20 mm diameter drill bit. As a procedure, the cutting action was investigated at three different regions of the drill point, namely cutting lips, secondary cutting edges and indentation zone. The models employed the analytical approach to account for the drill-bit geometry and cutting parameters, and an empirical approach to account for the material and friction properties. To complete the procedure, calibration experiments were conducted on bovine cortical femurs with two different spindle speeds (1000 and 3000 r/min) and feeds (0.03 and 0.06 mm/rev), and then the specific normal and friction coefficients were determined. The developed mechanistic models were validated with different ranges of parameters (500–3500 r/min speeds, and 0.02–0.07 mm/rev feeds) those commonly involved in manual and robot-assisted surgery. The validation study revealed that the thrust forces predicted using the mechanistic models showed a maximum error of only 5.80%. However, the torques predicted from the mechanistic model found with more error than the thrust forces. The predominant reasons for this under-prediction might because of the extrapolation used to determine the specific cutting pressures, slip-line field applied to the indentation zone instead of compressive fracture, and chip clogging involved during the bone drilling as demonstrated in earlier studies. Despite the deviations, the developed mechanistic models satisfactorily follow the trends of the thrust forces and torques experienced during bone drilling. The outcomes can be used to practice the bone drilling procedure and monitor the effect of process parameters on thrust forces and torques in the in-silico environment before performing actual surgery.

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