Chinese Journal of Tissue Engineering Research ›› 2022, Vol. 26 ›› Issue (15): 2302-2306.doi: 10.12307/2022.580

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Effect of loading mode on stress distribution in head and neck of the femoral stem

Xie Fei1, Jia Peng2, Liu Jiaxin1, Liu Lu3, Zhang Chunqiu1, Ye Jinduo1   

  1. 1Tianjin Key Laboratory of Advanced Mechanical and Electrical System Design and Intelligent Control, National Experimental Teaching Demonstration Center of Mechanical and Electrical Engineering, School of Mechanical Engineering, Tianjin University of Technology, Tianjin 300384, China; 2Tianjin Hospital, Tianjin 300350, China; 3Tianjin Key Laboratory of Bone Implant Interface Functionalization and Personality Research, Just Huajian Medical Equipment (Tianjin) Co., Ltd., Tianjin 300190, China
  • Received:2021-08-20 Revised:2021-08-23 Accepted:2021-09-30 Online:2022-05-28 Published:2022-01-05
  • Contact: Zhang Chunqiu, MD, Professor, Tianjin Key Laboratory of Advanced Mechanical and Electrical System Design and Intelligent Control, National Experimental Teaching Demonstration Center of Mechanical and Electrical Engineering, School of Mechanical Engineering, Tianjin University of Technology, Tianjin 300384, China
  • About author:Xie Fei, Master candidate, Tianjin Key Laboratory of Advanced Mechanical and Electrical System Design and Intelligent Control, National Experimental Teaching Demonstration Center of Mechanical and Electrical Engineering, School of Mechanical Engineering, Tianjin University of Technology, Tianjin 300384, China Jia Peng, Master, Attending physician, Tianjin Hospital, Tianjin 300350, China Xie Fei and Jia Peng contributed equally to this work.
  • Supported by:
    the Science and Technology Support Project of Tianjin City, No. 18YFZCS00890 (to LL); Major Biomedical Engineering Project of Science and Technology Plan in Tianjin, No. 18ZXSGSY00010 (to LL [project participant]); Key Laboratory Open Fund of Tianjin City, No. SY-04-201902-003 (to JP [project participant]) and SY-04-201901-003 (to JP)

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Abstract: BACKGROUND: At present, the model and loading mode used in the numerical calculation of the femoral stem are not consistent with the experimental standard. The current finite element calculation standard of the femoral stem, ASTM F2996-2013/YY/T 1714 2020, specifies that the computational model for the femoral stem prosthesis of the hip joint is a single femoral stem, and the loading mode is the rigid zone loading. The model specified in the experimental standard YY/T 0809.6-2018/ISO7206:2013 includes femoral stem, ball head and platen, and the loading mode is displacement loading. Inconsistency between computational and experimental models leads to a large difference between the calculation and experimental results. When the computational model is consistent with the experimental model and the same loading mode is used in the two models, the difference between the two model results is significantly reduced. This indicates that the computational model and its loading mode designed based on ASTM F2996-2013/YY/T 1714 2020 still have obvious defects.  
OBJECTIVE: To investigate the effect of different loading modes on stress distribution in the head and neck of the femoral stem, reduce the error of calculation results and experimental results, and replace the existing standard of numerical calculation of the femoral stem by the ball head pressing plate model and displacement loading mode, thereby improving the calculation accuracy.
METHODS:  Numerical simulation: The rigid zone loading and displacement loading were applied to the two computational models of single femur stem and femur stem ball head pressing plate by using the finite element analysis software ANSYS APDL, respectively, to obtain the law of stress distribution in the head and neck of the femoral stem under the two models and different loading modes. Electrical testing: the strain value was obtained through a strain sheet attached at the stem neck when the femoral prosthesis stem was loaded by the ball head pressing plate. The computational model and loading mode close to the experimental results were determined by comparing the calculation results with the experimental results.  
RESULTS AND CONCLUSION: The femoral stem ball head pressing plate model showed a stress peak of 504 MPa at the neck of the femoral stem under displacement loading mode. The maximum tensile stress was mainly concentrated on the lateral head and neck, and the maximum compressive stress was mainly concentrated on the medial head and neck. The single femoral stem model showed a stress peak of 562 MPa at the neck of the femoral stem under the rigid zone loading. The maximum tensile stress was mainly concentrated on the lateral head and neck, the maximum compressive stress was mainly concentrated on the medial head and neck, and the stress distribution law was close to that of the displacement loading mode. In the electrical testing, the strain value was -581.96 με on the medial head and neck and 666.00 με on the lateral head and neck. The inner strain value was -834.91 με and the outer strain value was 724.32 με under the displacement loading mode corresponding to the position of strain sheet. Under the rigid zone loading, the inner strain value was -992.32 με, and the outer strain value was 1 006.97 με. To conclude, the results of the ball head pressing plate model and the displacement loading mode are relatively close to the experimental results and should be used as the standard for the finite element calculation of the femur stem.

Key words: femoral stem head and neck, rigid zone loading, displacement loading, stress, strain

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