RÉSUMÉ
BACKGROUND: Most current studies of orthopedic screw parameters focus on mechanical properties but lack biocompatiblllty assessment. OBJECTIVE: To Investigate the Influence of geometric parameters and material properties of orthopedic screws on blomechanical compatibility, explore the optimal combination of various factors and parameterization levels, providing a theoretical reference for the design of orthopedic screws. METHODS: An orthogonal experiment protocol was designed according to the five factors and three parameterization levels of orthopedic screws. Factor A was the screw diameter (4.5, 5.5, 6.5 mm), factor В was thread profile (rectangular, trapezoidal, triangular), factor С was screw pitch (1.75, 2.25, 2.75 mm), factor D was the thread depth (0.5,1.0,1.5 mm), and factor E was elastic modulus (45,110, 200 GPa). The blomechanical finite element analysis of the three-dimensional bone-nail model under different sets of screw parameters was carried out. Stress distribution and two experimental indicators (the stress transfer parameter STPa between the cortical bone and the screw, and the stress transfer parameter STPß between the cancellous bone and the screw) under different experimental schemes were obtained. The weighted matrix analysis method was used to analyze the orthogonal experimental data to obtain the influence law and the optimal combination. RESULTS AND CONCLUSION: Different levels of different factors have different degrees of influence on biocompatiblllty. Among them, the screw material properties are the most Important factors, followed by the thread profile, pitch and thread diameter, and the last was the thread depth. The thread profile, pitch, and thread diameter had similar influence on biocompatiblllty. The optimal combination of the orthogonal experiment was an orthopedic screw with a large diameter of 6.5 mm, a trapezoidal thread, a pitch of 2.75 mm, a thread depth of 0.5 mm, and an elastic modulus of 45 GPa.
RÉSUMÉ
In order to evaluate the biomechanical stability of titanium alloy screw with different structural parameters under bone remodeling, some three-dimensional finite element models were established and the bone remodeling process after implanting the screw was simulated. Three-dimensional finite element models consist of bone and screw with different lengths and diameters. Bone remodeling process was simulated by user-defined subroutine. It is found that the stress on the bone is concentrated on the groove and root of the internal thread. The screw stress is mainly on the beginning of the thread, and the whole stress decreases along the long axis of the screw. The stress distribution trend of bone and screw did not change significantly during the bone remodeling. The maximum equivalent stress value was different, the maximum equivalent stress on the screw and cancellous bone increased while the maximum equivalent stress value on the cortical bone decreased.