This article aims to compare and analyze the biomechanical differences between wing-shaped titanium plates and traditional titanium plates in fixing acetabular anterior column and posterior hemi-transverse (ACPHT) fracture under multiple working conditions using the finite element method. Firstly, four sets of internal fixation models for acetabular ACPHT fractures were established, and the hip joint stress under standing, sitting, forward extension, and abduction conditions was calculated through analysis software. Then, the stress of screws and titanium plates, as well as the stress and displacement of the fracture end face, were analyzed. Research has found that when using wing-shaped titanium plates to fix acetabular ACPHT fractures, the peak stress of screws decreases under all working conditions, while the peak stress of wing-shaped titanium plates decreases under standing and sitting conditions and increases under forward and outward extension conditions. The relative displacement and mean stress of the fracture end face decrease under all working conditions, but the values are higher under forward and outward extension conditions. Wing-shaped titanium plates can reduce the probability of screw fatigue failure when fixing acetabular ACPHT fractures and can bear greater loads under forward and outward extension conditions, improving the mechanical stability of the pelvis. Moreover, the stress on the fracture end surface is more conducive to stimulating fracture healing and promoting bone tissue growth. However, premature forward and outward extension rehabilitation exercises should not be performed.
Titanium ; Bone Plates ; Humans ; Acetabulum/surgery* ; Fracture Fixation, Internal/methods* ; Biomechanical Phenomena ; Finite Element Analysis ; Bone Screws ; Fractures, Bone/surgery* ; Stress, Mechanical ; Working Conditions

Objectives:To analyze the mechanical properties of the personalized artificial vertebral body of 3D-printed poly etheretherketone(PEEK)matrix composites after implantation and its effect on adjacent tissues using finite element analysis.Methods:The CT scan data of a healthy male volunteer was extracted for 3D reconstruction,the finite element model of the lumbar spine(L1-L5)was constructed,and the ranges of motion of different lumbar vertebrae segments in various motion states were simulated,after that,the effectiveness of the finite element model was verified by comparing with the research data in previous studies.The total en bloc spondylectomy(TES)was simulated to remove the L3 vertebral body and adjacent intervertebral discs,and a personalized artificial vertebral body was designed based on the design principles of artificial vertebral body and was fixed to the adjacent lumbar segments using a posterior approach with a titanium alloy rod-screw system.The interior of the artificial vertebral body was designed as honeycomb structures with densities of 30％,50％,and 70％.PEEK/hydroxylaptite(HA)composite materials were selected as the external shell of the personalized lumbar artificial vertebral body,and PEEK/carbon fiber(CF)materials were used as the internal filler.The forces and moments of each vertebral body in the upright,forward bending,backward extension,lateral bending and rotation states were obtained through the Vicon Nexus system,and as the boundary con-ditions of finite element analysis,the appropriate size of the bone graft hole and the thickness of the shell were selected,and then the inside of the artificial vertebral body was filled with hexagonal honeycombs of different densities.The models of young and middle-aged and elderly groups were established by changing the elastic modulus of cortical bone and cancellous bone,and the finite element simulation was carried out on the models.The maximum stress values of the artificial vertebral body,fixation system and adjacent upper and lower endplates under different motion states,and the stress occlusion rate of the artificial vertebral body were analyzed to evaluate the performance of the artificial vertebral body.Results:The maximum stress value of artificial vertebral body(42.25MPa)was lower than the yield strength of PEEK/HA(65MPa),and the maximum stress value of internal honeycomb(26.38MPa)was lower than the yield strength of PEEK/CF(90MPa);The maximum stress value of rod-screw system(271.75MPa)was lower than the yield strength of titanium alloy(900MPa),and the maximum stress value of the endplate on adjacent endplate(7.87MPa)was lower than the yield strength of cartilage endplate(50MPa).The stress occlusion rate of artificial vertebral body with 30％honeycomb density in the middle-aged and elderly group was the lowest.Conclusions:The 3D-printed personalized artificial vertebral body of PEEK matrix composite can complete the structure reconstruction of lumbar spine well after TES with good biomechanical stability.

Objectives:To analyze the mechanical properties of the personalized artificial vertebral body of 3D-printed poly etheretherketone(PEEK)matrix composites after implantation and its effect on adjacent tissues using finite element analysis.Methods:The CT scan data of a healthy male volunteer was extracted for 3D reconstruction,the finite element model of the lumbar spine(L1-L5)was constructed,and the ranges of motion of different lumbar vertebrae segments in various motion states were simulated,after that,the effectiveness of the finite element model was verified by comparing with the research data in previous studies.The total en bloc spondylectomy(TES)was simulated to remove the L3 vertebral body and adjacent intervertebral discs,and a personalized artificial vertebral body was designed based on the design principles of artificial vertebral body and was fixed to the adjacent lumbar segments using a posterior approach with a titanium alloy rod-screw system.The interior of the artificial vertebral body was designed as honeycomb structures with densities of 30％,50％,and 70％.PEEK/hydroxylaptite(HA)composite materials were selected as the external shell of the personalized lumbar artificial vertebral body,and PEEK/carbon fiber(CF)materials were used as the internal filler.The forces and moments of each vertebral body in the upright,forward bending,backward extension,lateral bending and rotation states were obtained through the Vicon Nexus system,and as the boundary con-ditions of finite element analysis,the appropriate size of the bone graft hole and the thickness of the shell were selected,and then the inside of the artificial vertebral body was filled with hexagonal honeycombs of different densities.The models of young and middle-aged and elderly groups were established by changing the elastic modulus of cortical bone and cancellous bone,and the finite element simulation was carried out on the models.The maximum stress values of the artificial vertebral body,fixation system and adjacent upper and lower endplates under different motion states,and the stress occlusion rate of the artificial vertebral body were analyzed to evaluate the performance of the artificial vertebral body.Results:The maximum stress value of artificial vertebral body(42.25MPa)was lower than the yield strength of PEEK/HA(65MPa),and the maximum stress value of internal honeycomb(26.38MPa)was lower than the yield strength of PEEK/CF(90MPa);The maximum stress value of rod-screw system(271.75MPa)was lower than the yield strength of titanium alloy(900MPa),and the maximum stress value of the endplate on adjacent endplate(7.87MPa)was lower than the yield strength of cartilage endplate(50MPa).The stress occlusion rate of artificial vertebral body with 30％honeycomb density in the middle-aged and elderly group was the lowest.Conclusions:The 3D-printed personalized artificial vertebral body of PEEK matrix composite can complete the structure reconstruction of lumbar spine well after TES with good biomechanical stability.

BACKGROUND:In general, a single-type artificial bone is difficult to meet the requirements for bone defect repair and extracellular matrix of bone tissue engineering. Compositing and processing the materials with different properties can form the composite-type artificial bone, which can either ensure the biological activity or effectively improve its mechanical properties.OBJECTIVE: To summarize the present situation of the application of composite-type artificial bone and prospects the development trend. METHODS:The literatures were retrieved from CNKI, ScienceDirect, PubMed, SpingerLink, El Village, Wiley databases from January 2000 to April 2017. The key words were "composite scaffold, tissue engineering, artificial bone" in Chinese and English, respectively. The selected literatures were analyzed according to the inclusion and exclusion criteria. RESULTS AND CONCLUSION: The requirements for the scaffolds used for bone tissue engineering are complex and it should carefully consider and control various factors used in the design and preparation of scaffolds, including microporous structure, mechanical strength, degradation rate, porosity, growth factor, morphology and surface chemistry, so as to meet the bone tissue engineering applications. The preparation of tissue-engineered bone scaffold is based on biological active substances and matrix materials through a reasonable manner. It simulates the components of natural bone matrix, promotes the adhesion, proliferation and differentiation of bioactive substances, and gives play to its functions of osteogenesis. Although existing techniques and methods have made significant progress in the preparation of composite scaffolds, there is no technique or method to fully meet all the requirements for preparation of tissue-engineered bone scaffold.

Objective To analyze the influence of microporous parameters on mechanical behavior of bone tissue engineered-scaffolds, and provide references for optimizing the microporous structure design. Methods The finite element models of scaffolds with microporous structures were established by using ANYSYS software. The relationships between porosity and maximum equivalent stress as well as maximum total deformation were calculated. The effects of microporous spacing and diameter on maximum equivalent stress, maximum total deformation and internal strain were compared and analyzed. Results The influence rule of microporous spacing in x and y direction was consistent. With the increase of microporous spacing from 0.6 mm to 2.0 mm, the maximum equivalent stress reduced from 63.1 MPa to 46.3 MPa, the maximum total deformation reduced from 23.8 μm to 21.8 μm, and the proportion of the best strain range increased from 80% to 84%. However, with the increase of microporous spacing in z direction, the maximum equivalent stress increased from 38.3 MPa to 47.8 MPa, the maximum total deformation increased from 20. 8 μm to 22.8 μm, and the proportion of the best strain range fluctuated within the range of 82%-85%. With the increase of microporous diameter in x and y direction from 0.1 mm to 1.0 mm, the maximum equivalent stress increased from 32.4 MPa to 78.4 MPa, the maximum total deformation increased from 19.9 μm to 38.2 μm, and the proportion of the best strain range reduced from 90% to 53%. With the increase of microporous diameter in z direction, the maximum equivalent stress reduced from 58.8 MPa to 37.9 MPa, the maximum total deformation increased from 23.3 μm to 25.9 μm, and the proportion of the best strain range increased from 82% to 87%. Conclusions The greater the porosity and the proportion of the best strain range, the smaller maximum equivalent stress and maximum total deformation would be, the scaffolds would have the better biological and mechanical properties. These results have reference values for design and optimization of scaffold structure.