ABSTRACT
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.
ABSTRACT
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.
Subject(s)
Biomechanical Phenomena , Bone Remodeling , Bone Screws , Finite Element Analysis , Stress, Mechanical , TitaniumABSTRACT
Objective To explore the effects of screw configurations on bone healing, so as to provide the basis for related fracture treatment. Methods The process of bone healing under different screw configurations was studied by finite element method, and the change in the process of callus growth during healing periods was simulated by interfragmentary strain theory (IFS). The iterative process for renewing callus modulus in every finite element was conducted by the second-developed ABAQUS based on Python scripting language, thus the process of fracture healing was simulated. Results The effect from different numbers of screws on bone healing was smaller than that from different working length of bone plates. On the premise of stable fixation, given the certain working length of bone plates, the effect from different screw numbers on stress distributions in plates or screws was relatively small, while the effect from different working length on stress distributions in plates or screws was relatively large, and the stress distribution in plates was larger than that in screws at different working length. Conclusions It is necessary to take more consideration on working length of bone plates than the number of screws when they are under a stable fixed situation, and it is a wise choice to reduce the screw numbers and choose a suitable working length for bone healing process.