On the Effect of Contact Stress in a Total Knee Replacement Considering Surface Roughness

The excessive wear of the polyethylene surface is known as one of the main reasons for the total knee replacement (TKR). The rate of wear is critically dependent on factors including surface roughness, real contact area, contact stress, material properties and thickness of the polyethylene inlay. In the present research, surface roughness is studied as a pivotal point in computing contact stresses. Surface roughness is analytically simulated using various asperity shape models. Finite element analysis is also implemented assuming two different types of material properties namely; the elastic-perfect plastic and elastic-nonlinear hardenings then the analytical and FEM results are compared. The actual surface of a sample of TKR is measured by the profilometer experimentally. Measured profiles are approximated by mathematical functions and the contact problem of the TKR is then solved. The actual pressure distribution and the real contact area are calculated for each asperity using deterministic multi-level approach. Finally, the effect of roughness between contacting surfaces of femoral and tibial components of the TKR on the stress distribution is studied that has not been fully addressed in previous works. It is observed that small contact loads may cause plastic deformation in peaks especially sharp asperities of actual surfaces. Plastic deformation leads to excessive wear on the contacting surfaces and results serious damage to the knee joint prosthesis.

Keywords:

Contact Mechanics , Joint Prosthesis , Surface Roughness , Total Knee Replacement , Finite Element Method