Finite element analysis of functionally graded materials for tibial prosthesis
Li Zhi1, Chen Weiyi1, Wang Chenyan1, Xiang Changxin1, Lan Weiwei1, Wang Changjiang2, Guo Yuan1
1College of Biomedical Engineering, Taiyuan University of Technology, Taiyuan 030024, Shanxi Province, China; 2College of Engineering and Information, University of Sussex, Brighton, BNI 9RH, UK
Abstract: BACKGROUND: Excessive wear of the tibial insert and aseptic loosening of the prosthesis were the main reasons for the failure of the knee prosthesis after total knee arthroplasty. Owing to the large variation of mechanical strength between prosthesis and bone, it would lead to stress shielding on bone, and then induce aseptic loosening of prosthesis.
OBJECTIVE: To analyze the stress response of cancellous bone in proximal tibia after functionally graded materials (FGMs) tibial prosthesis implantation by finite element method.
METHODS: Two FGMs with different porosity parameters (FGM I and FGM III) were designed using titanium-hydroxyapatite composite. The other was prepared by titanium-ideal bone repairing material and named FGM II. The porosity parameters of FGM I were 0.1, 1 and 1, and the porosity parameters of FGM II and FGM III were 0.4, 0 and 1. A three-dimensional finite element model of total knee arthroplasty was established, and the stress distributions of FGM and titanium alloy tibial prostheses were analyzed by Abaqus software under three working conditions of 0° extension, 30° and 60° flexion.
RESULTS AND CONCLUSION: (1) The maximum Von Mises stresses of FGM tibial prostheses were significantly lower than those of titanium alloy tibial prosthesis, and the stresses at the contact zone between the cancellous bone and the stem end were significantly reduced in FGM tibial prostheses groups. (2) According to the stress curve and average stress of the cancellous bone of the tibia along different paths, the stresses of the cancellous bone of the proximal tibia were increased in FGM tibial prostheses groups compared with titanium alloy tibial prostheses, under different working conditions. Specifically, FGM I was increased by 5.4%-17.3%; FGM II was increased by 1.0%-13.5%; and FGM III was increased by 1.6%-15.4%. (3) The results illustrated that FGM prostheses could increase the stress on the cancellous bone of the proximal tibia and reduce the stress shielding effect of the proximal tibia. Therefore, the risk of aseptic loosening was decreased and the availability of the prosthesis was prolonged. Specifically, FGM I tibial prosthesis was the best among the three kinds of FGM prostheses.
Key words: functionally graded materials, tibial prosthesis, finite element, stress, stress shielding, aseptic loosening, knee prosthesis