Experimental and Theoretical Study of the Contact Mechanics of Five Total Knee Joint Replacements

Abstract

The tibio-femoral contact area in five current popular total knee joint replacements has been measured using pressure-sensitive film under a normal load of 2.5 kN and at several angles of flexion. The corresponding maximum contact pressure has been estimated from the measured contact areas and found to exceed the point at which plastic deformation is expected in the ultra-high molecular weight polyethylene (UHMWPE) component, particularly at flexion angles near 90 degrees. The measured contact area and the estimated maximum contact stress have been found to be similar in magnitude for all of the five knee joint replacements tested. A significant difference, however, has been found in maximum contact pressure predicted from linear elasticity analysis for the different knee joints. This indicates that varying amounts of plastic deformation occurred in the polyethylene component in the different knee designs. It is important to know the extent of damage as knees with large amounts of plastic deformation are more likely to suffer low cycle fatigue failure. It is therefore concluded that the measurement of contact areas alone can be misleading in the design of and deformation in total knee joint replacements. It is important to modify geometries to reduce the maximum contact stress as predicted from the linear elasticity analysis, to below the linear elastic limit of the plastic component.

Effect of conformity and contact stress on wear in fixed-bearing total knee prostheses

“…The extent of delamination is affected by various factors including high contact stress and low congruity (Walker, 1988;Bartel et al, 1986). Experimental (Stewart et al, 1995) and theoretical (Jin et al, 1995a, b) studies have shown that as geometries become less conforming the values of peak contact stress approach and exceed the yield stress of UHMWPE making it more prone to fatigue failure.…”

The influence of design, materials and kinematics on the in vitro wear of total knee replacements

“…Improvements in total knee replacement (TKR) designs, materials and sterilisation techniques during the past decade have led to improved clinical performance of these prostheses by reducing the prevalence of delamination and structural fatigue of the ultra high molecular weight polyethylene (UHMWPE) bearings (Stewart et al, 1995;Won et al, 2000;Reeves et al, 2000;Bell et al, 1998). However, in the longer term, concern remains regarding the surface wear of total knee components as the generation and accumulation of micrometre and submicrometre size wear particles has been observed in tissues surrounding knee replacements which were revised for infection in the early years of implantation (Howling et al, 2001).…”

Prediction of scratch resistance of cobalt chromium alloy bearing surface, articulating against ultra-high molecular weight polyethylene, due to third-body wear particles

“…It was assumed that the boundary conditions (including loading) applied to the third-body wear particle (micro-model ) were determined from the contact between the two articulating surfaces (macro-model ). The contact pressure between the two articulating surfaces, which has been reported for both hip and knee implants employing UHMWPE components in previous studies [19][20][21], was used as an input condition to the present micro-model. Figure 1b shows the local set-up of the micro-model from which a simple twodimensional axisymmetric nite element model (as shown in Fig.…”