Orthopedic screw parameters in the orthogonal test:
biocompatibility evaluation

doi:10.3969/j.issn.2095-4344.1887

Abstract

Abstract:

BACKGROUND: Most current studies of orthopedic screw parameters focus on mechanical properties but lack biocompatibility assessment.

OBJECTIVE: To investigate the influence of geometric parameters and material properties of orthopedic screws on biomechanical 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 B was thread profile (rectangular, trapezoidal, triangular), factor C 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 biomechanical 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 STPα between the cortical bone and the screw, and the stress transfer parameter STPβ 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 biocompatibility. 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 biocompatibility. 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.

Key words: orthopedic screw, biocompatibility, stress transfer parameter, finite element analysis, orthogonal experiment, intuitive analysis, analysis of variance, weight matrix method

CLC Number:

Long Dengyan, Ji Aimin, Zhao Zhonghang, Fang Runxin, Chen Changsheng. Orthopedic screw parameters in the orthogonal test: biocompatibility evaluation[J]. Chinese Journal of Tissue Engineering Research, 2020, 24(10): 1574-1579.

Figures/Tables 6

查得临界值F0.10(2，7)=3.257 4，F0.05(2，7)=4.737 4，F0.01(2，7)=9.546 6，F0.05(2，7)<FA、FB、FD、FE、F0.01(2，7)FC< F0.10(2，7)，可见因素A、B、D、E对考察指标STPα均有显著影响，只有因素C对考察指标STPα无显著影响。 2.2.3 权矩阵法综合评价分析试验数据可知，因素E即接骨螺钉弹性模量的影响高度显著，其余不同因素对于皮质骨-螺钉的应力传递与松质骨-螺钉的应力传递的影响程度不一样。因此，需要对上述两指标进行综合考量。权矩阵法可以计算出影响试验结果的考察指标权重，根据权重大小可快速有效的得出试验的最佳方案以及各因素对于正交试验指标值影响的主次顺序，因此采用权矩阵法来确定因素的主次顺序及最佳方案。根据文献[22]计算方法，对权函数ω进行求解。第一个试验考察指标为皮质骨-螺钉的应力传递参数STPα，其值越大越好，权矩阵ω1计算结果如下： ω1T=[0.031 673，0.035 123，0.036 57，0.042 616，0.047 011，0.039 383，0.066 637—0.066 634，0.089 348，0.026 354，0.029 613，0.029 719，0.204 629，0.146 755，0.107 934] 第二个实验考察指标为松质骨-螺钉的应力传递参数STPβ，其值越大越好，权矩阵ω2计算结果如下： ω2T=[0.062 422，0.075 163，0.085 408，0.085 627，0.082 278，0.061 335，0.029 311—0.030 391，0.033 31，0.085 074，0.068 595，0.063 311，0.095 059，0.073 79，0.068 925] 正交试验考察指标的总权矩阵为2个指标值的权矩阵的平均值，计算如下： ωT=[0.047 048，0.055 143，0.060 989，0.064 122，0.064 645，0.050 359，0.047 974—0.048 512，0.061 329，0.055 714，0.049 104，0.046 515，0.149 844，0.110 273，0.088 429] =[A1，A2，A3，B1，B2，B3，C1，C2，C3，D1，D2，D3，E1，E2，E3] 综合计算上述可知，因素A的3个水平对试验结果的影响权重分别为：A1=0.047 048，A2=0.055 143，A3=0.060 989，A3权重最大；同理，因素B中B2权重最大，因素C中C3权重最大，因素D中D1权重最大，因素E中E1权重最大。由此可知，本正交试验的最优方案为A3B2C3D1E1，即大径为6.5 mm、梯形螺纹、螺距为2.75 mm、螺纹深度为0.5 mm、弹性模量为45 GPa的接骨螺钉生物力学性能表现最佳。同时可得出各个因素对于试验考察指标影响的主要次序为E、B、C、A、D，即弹性模量对试验指标的影响最大，其次是螺纹牙型、螺距和螺纹直径并且其影响程度相近，而螺纹深度影响最小。 "

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