Speaker
Description
Introduction Hip fractures, especially those caused by age-related pathological disease, are severe conditions, associated with severe quality of life reduction and high mortality rates. The growing incidence rate of such conditions greatly concerns national health systems, due to high surgical costs and prolonged hospitalization. Basicervical femoral neck fractures, a relatively rare type of hip fractures, are associated with high internal failure fixation rates, due to the inherent rotational instability of the fracture pattern. It has been shown that, during lag screw insertion for internal fixation, the femoral head may rotate with relation to the femoral neck, leading to greater risk malunion or nonunion and finally, of implant failure post-surgery. Scope This work focuses on the finite element modelling of a novel surgical technique of lag screw insertion developed by the orthopedic department at the university hospital of Patras, with the goal of limiting the relative rotation between femoral head and neck. Then, a simulation of a robotic arm performing the insertion of the lag screw is developed, to demonstrate potential feasibility of such a system. Methodology Quantitative CT scans (QCT) scans of the proximal femur from a previous study were segmented and a 3D CAD model of the proximal femur was generated, in which a virtual fracture line, indicative of a basicervical femoral fracture, was created. The geometry was meshed, and an inhomogeneous Young’s modulus distribution was obtained from the radiological density of the QCT scans. Using a coordinate-measuring machine (CMM), a 3D CAD model of the Gamma3 lag screw by Strycker was obtained and positioned according to manufacturer guidelines in the virtual model. The Finite Element (FE) model simulated the insertion procedure of the lag screw with boundary conditions according to the novel surgical technique. The equivalent environmental stiffness of the system was estimated from the results of the model and consequently used to design a hybrid position/force controller for a KUKA IIWA robotic arm, which was tested in a simulation environment. Results The maximum relative displacement between the femoral head and femoral stem fracture surfaces was 1.55μm, suggesting that the proposed surgical technique could be effective in limiting relative sliding. Maximum relative displacement was observed during initial sliding of the lag screw inside the femur, suggesting that one continuous motion of rotation for insertion could be beneficial for better outcomes. The maximum position error of the position controller of the end-effector motion was smaller than 1%, while the maximum error in tractive force developed along the main screw axis was 10%. Conclusions These results indicate the potential benefit of a hybrid surgical system, in which the surgeon would initiate lag screw insertion, and a robotic arm would complete the procedure, for basicervical hip fractures and the potential benefits of a patient-specific, physics-based, pre-operative planning protocol.
