Design, manufacture and experimental analysis of cementless hip prosthesis in torsional force transmission

doi:10.3969/j.issn.2095-4344.2016.39.003

Abstract

Abstract:

BACKGROUND: Human femur medullary cavity has torsional anatomic structure. If the femur medullary cavity’s torsional structure is copied to the stem of the prosthesis, the prosthesis will transform the force loaded to torque between femur medullary cavity and prosthesis stem, and the torque is transmitted to the proximal femur when the prosthesis is inserted in the medullary cavity and load force on the prosthesis.

OBJECTIVE: To optimize the force transmission of the proximal femur, and to avoid the stress shielding at the proximal end of the prosthesis.

METHODS: We reconstructed a three-dimensional (3D) model of the femoral canal with the CT images of specimen femur and took the 3D model as the design model for prosthesis stem. The customized stem model and the proximal model of standard prosthesis could be put together to form customized prosthesis. We took advantage of robot grinding technology to manufacture the customized prosthesis, and matched it with specimen femur canal. Finite element analysis simulation and experimental methods were used to analyze the relationship between the loading force on the prosthesis and the micromotion of proximal end of the prosthesis.

RESULTS AND CONCLUSION: The simulation and experimental results showed that the torsional structure matching by femoral canal and stem could effectively transmit the force on the prosthesis to the proximal end of the prosthesis in the form of torque. The torsional fretting of the proximal end of the prosthesis was related to the movement of the handle body. However, stem micromotion can be controlled by varying the matching size between stem and medullary cavity.

中国组织工程研究杂志出版内容重点：人工关节；骨植入物；脊柱；骨折；内固定；数字化骨科；组织工程

Key words: Hip Prosthesis, Finite Element Analysis, Tissue Engineering

CLC Number:

R318

Pang Bang, Wu Qi, Guan Xiao-dong, Xi Wen-ming. Design, manufacture and experimental analysis of cementless hip prosthesis in torsional force transmission[J]. Chinese Journal of Tissue Engineering Research, 2016, 20(39): 5794-5800.

Figures/Tables 3

将设计的定制式假体与股骨模型导入Pro-E 软件 (Parametric Technology Company，USA)进行装配，然后，将装配好的模型导入Ansys Workbench 14.5软件(Ansys Company，USA)赋材质并进行网格划分，其中股骨的模量设置为2×1010 Pa，假体的模量设置为11× 1010 Pa。在装配模型的假体顶端加载力，可得到柄体微动与假体上加载的力的关系。由于在有限元分析软件中无法得到柄体微动，实验采用如下的方法得到柄体微动与假体上加载力的关系：首先在股骨模型上做标记点，其次在有限元软件中剖开未加载力时股骨与假体的匹配模型，测量标记点与假体模型末端的距离，最后，在有限元软件中剖开加载不同力的股骨与假体匹配模型，测量标记点与假体模型末端的距离，将加载力的测量距离与未加载力的测量距离相减，可以得到柄体微动与假体上加载力的关系，见图3所示。在图3中，全长匹配是指柄体整个长度与髓腔匹配，而半长匹配是指柄体的一半长度与髓腔匹配。从图3可以看出，柄体的微动随着假体上加载力的增加而增加，随着柄体匹配区的增加而减小。这样，通过改变匹配区的大小，就可以控制柄体的微动，从而控制柄体的扭转微动。根据柄体断面的 0.32 (°)/mm扭转角度，得到假体近端扭转微动=微动× 0.32×假体的轴线到假体近端表面的最大距离×2π/360。参考图3中的半长匹配的微动曲线，当假体上加载300，500，800 N力时，假体近端相对髓腔的扭转微动为19.5，27.9，44.5 µm，计算时，假体的轴线到假体近端表面的最大距离是10 mm。图4是将股骨远端固定，在匹配区的柄体上加载扭转力，使柄体相对髓腔的扭转微动和计算的扭转微动相同。从图4可以看出，当假体上加载300，500，800 N力时，柄体产生的扭转微动都可以传递到股骨近端。这是因为大模量的假体总是将扭转力向远离扭转力加载点的地方传递，当扭转力加载在假体远端时，该扭转力被传递到股骨近端。"

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