Customized surface-guided knee implant: Contact analysis and experimental test

• Published in: Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine Part H: Journal of Engineering in Medicine, 2018-01, Vol.232 (1), p.90-100
• Main Authors: Khosravipour, Ida, Pejhan, Shabnam, Luo, Yunhua, Wyss, Urs P
• Format: Article
• Language: English
• Subjects: Activities of daily living; Biomedical materials; Contact; Contact pressure; Contact stresses; Crack propagation; Fatigue; Fatigue failure; Finite element analysis; Finite element method; Kinematics; Knee; Mathematical analysis; Mathematical models; Polyethylene; Pressure; Stress analysis; Stress concentration; Stress distribution; Surgical implants; Tibia; Transplants & implants; Ultra high molecular weight polyethylene; Ultrasonic testing; Walking; Wear
• ISSN: 0954-4119; 2041-3033
• DOI: 10.1177/0954411917744586

Contact pressure and stresses on the articulating surface of the tibial component of a total knee replacement are directly related to the joint contact forces and the contact area. These stresses can result in wear and fatigue damage of the ultra-high-molecular-weight polyethylene. Therefore, conducting stress analysis on a newly designed surface-guided knee implant is necessary to evaluate the design with respect to the polyethylene wear. Finite element modeling is used to analyze the design’s performance in level walking, stair ascending and squatting. Two different constitutive material models have been used for the tibia component to evaluate the effect of material properties on the stress distribution. The contact pressure results of the finite element analysis are compared with the results of contact pressure using pressure-sensitive film tests. In both analyses, the average contact pressure remains below the material limits of ultra-high-molecular-weight polyethylene insert. The peak von Mises stresses in 90° of flexion and 120° of flexion (squatting) are 16.28 and 29.55 MPa, respectively. All the peak stresses are less than the fatigue failure limit of ultra-high-molecular-weight polyethylene which is 32 MPa. The average contact pressure during 90° and 120° of flexion in squatting are 5.51 and 5.46 MPa according to finite element analysis and 5.67 and 8.14 MPa according to pressure-sensitive film experiment. Surface-guided knee implants are aimed to resolve the limitations in activities of daily living after total knee replacement by providing close to normal kinematics. The proposed knee implant model provides patterns of motion much closer to the natural target, especially as the knee flexes to higher degrees during squatting.