Mechanical response of polyethylene tibial component using compression loading contact test: experimental and finite element analysis.

An experimental apparatus has been developed to study the mechanical response of Total Knee Replacement (TKR) prosthesis under compression loading test (Tibial HDPE component and femoral Vitallium component). Analysis of experimental results indicates that the load-displacement curve depends on the initial contact location. The position of this curve varies between two curves of lower and higher stiffness. Experimental compression loading curve for femoral part resting on flat HDPE is located between the extreme curves. This result allows us to model load-displacement curve of TKR prosthesis under compression loading using femoral component resting on flat polyethylene surface. For simple contact geometry of spherical cap on flat HDPE specimen, Hertz elastic theory can be used to describe the load displacement curve for loads under 635 N. This value corresponds to the load which induces plastic flow of polyethylene. In the case of femoral component on flat HDPE specimen, Hertz elastic theory can be considered for loads under 800 N. Finite element 2D is also used to model the compression load displacement curve for femoral component resting on flat HDPE specimen. The finite element results are similar to the Hertz elastic theory analysis for compression loading under 1200 N. Damage of tibial component can be related to the critical load which induces plastic flow of polyethylene. This load depends on the contact geometry and can be estimated with the Hertz elastic theory.

Visualisation of tibiofemoral contact in total knee replacement using optical device.

An in situ optical visualization technique (OVT) has been developed to identify the tibiofemoral contact (TFC) area during prosthesis indentation. An artificial total knee replacement (TKR) with borosilicate glass femoral component has been reproduced similarly to the original one. The medial and lateral contact areas have been observed, located and measured by means of in situ OVT. Therefore, it was experimentally possible to ensure a good axial alignment of the femoral component and tibial polyethylene insert. In addition, experimental measurement for load-displacement curves became reproducible. Furthermore, the evolution of the medial and lateral TFC areas as a function of the normal load was established. Finally, this study has shown that the in situ OVT is a simple in vitro method that provides comparable results with well-known methods such as Fuji film technique.