Elsevier

Journal of Biomechanics

Volume 38, Issue 2, February 2005, Pages 357-365
Journal of Biomechanics

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

https://doi.org/10.1016/j.jbiomech.2004.02.015Get rights and content

Abstract

Debris-induced osteolysis due to surface wear of ultra high molecular weight polyethylene (UHMWPE) bearings is a potential long-term failure mechanism of total knee replacements (TKR). This study investigated the effect of prosthesis design, kinematics and bearing material on the wear of UHMWPE bearings using a physiological knee simulator. The use of a curved fixed bearing design with stabilised polyethylene bearings reduced wear in comparison to more flat-on-flat components which were sterilised by gamma irradiation in air. Medium levels of crosslinking further improved the wear resistance of fixed bearing TKR due to resistance to strain softening when subjected to multidirectional motion at the femoral–insert articulating interface. Backside motion was shown to be a contributing factor to the overall rate of UHMWPE wear in fixed bearing components. Wear of fixed bearing prostheses was reduced significantly when anterior–posterior displacement and internal–external rotation kinematics were reduced due to decreased cross shear on the articulating surface and a reduction in AP displacement. Rotating platform mobile bearing prostheses exhibited reduced wear rates in comparison to fixed bearing components in these simulator studies due to redistribution of knee motion to two articulating interfaces with more linear motions at each interface. This was observed in two rotating platform designs with different UHMWPE bearing materials. In knee simulator studies, wear of TKR bearings was dependent on kinematics at the articulating surfaces and the prosthesis design, as well as the type of material.

Introduction

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). This may lead to osteolysis and long-term failure mechanisms similar to those found in total hip replacements (Ingham and Fisher, 2000). The generation of UHMWPE wear debris from articulating surfaces in total knee replacements is affected by a number of factors. These include resultant knee motion, prosthesis design and bearing materials. Such factors have not previously been systematically analysed as a matrix of variables using physiological in vitro knee simulator testing.

Current TKR devices can be subdivided into two groups based on different fundamental design principles: fixed bearing knees, where the UHMWPE insert snap or press fits into the tibial tray, and mobile bearing designs which facilitate movement of the insert relative to the tray. In mobile bearing knees, motion of the knee is designed to occur at two articulating surfaces. Such designs differ according to the kinematics at the tray–insert interface and the resulting axis of rotation of the knee. Some mobile bearing designs allow both anterior–posterior translation and internal–external rotation at the tray–insert interface whereas in rotating platform mobile bearing knees rotation only is facilitated at the tray–insert counterface, hence reducing the degree of rotation at the femoral–insert articulation. The resulting kinematics at the articulating surfaces of the UHMWPE bearings from different prostheses differ greatly and UHMWPE wear is dependent on the kinematics to which the material is subjected (Wang et al., 1996).

This paper describes a series of studies which compared the wear of fixed bearing and rotating platform mobile bearing total knee prostheses with different bearing materials and under varied kinematic conditions using a physiological knee simulator. The effects of prosthesis design, bearing material, backside motion and kinematics on UHMWPE wear in TKR are discussed.

Section snippets

Materials

The wear of fixed bearing and rotating platform mobile bearing TKRs was investigated using commercially available designs (Fig. 1). The fixed bearing TKRs tested in these studies comprised PFC and PFC Sigma components. The PFC system, which was introduced clinically in the early 1980s, employed an essentially flat-on-flat femoral–insert configuration and used polyethylene, which was gamma irradiated in air. The PFC Sigma implant system was introduced with the femoral component being rounded in

Methods

The wear of fixed bearing and rotating platform mobile bearing TKRs was compared using the Leeds ProSim six-station force/displacement controlled knee simulators (Barnett et al., 2002). Six (n=6) TKR of a single design were tested on the simulator for most test conditions. Femoral axial loading (maximum 2600 N) and extension–flexion (0°–58°) input profiles were adopted from the ISO 14243 (2002) standard for all simulator studies (Fig. 2). The compressive load applied to each knee was offset 5 mm

Study 1: effect of fixed bearing design and materials

The PFC fixed bearing knees, which had inserts manufactured from 1020 UHMWPE and were sterilised by gamma irradiation in air and shelf aged for 29–33 months, exhibited a mean wear rate with 95% confidence limits of 41±14 cubic mm per million cycles (mm3/MC) when subjected to standard kinematics (Fig. 4). In contrast, a mean wear rate of 23±5.9 mm3/MC was observed for the PFC Sigma components with inserts manufactured from 1020 GVF polyethylene. This two-fold reduction in wear with the introduction

Effect of fixed bearing design and materials

The PFC total knee replacement is a non-conforming posterior-cruciate retaining prosthesis with a polyethylene insert that is essentially flat in the sagittal plane. Flat-on-flat articulations, while conforming when in perfect alignment, are susceptible to high edge loading during walking (Bartel et al., 1986). Schai et al. (1998) reported that survivorship of the PFC cruciate retaining knee after 10 years was 90%. However, this increased to 97% when metal-backed patellae and less conforming

Conclusions

The potential for long-term osteolysis in total knee replacement necessitates minimisation of the number of particles generated due to surface wear, particularly for implantation in younger, more active patients. These simulator studies have identified factors which affect the in vitro wear of polyethylene and may also affect in vivo behaviour of total knee replacements. More conforming coronal geometry and use of stabilised polyethylene bearings significantly decreased the volumetric wear rate

Acknowledgements

DePuy International, a Johnson and Johnson Company, provided a studentship for H.M.J. McEwen. Funding for these studies was received from the Engineering and Physical Sciences Research council UK and the Arthritis Research Campaign UK.

References (20)

  • C.J. Bell et al.

    The effect of oxidation on delamination of UHMWPE tibial components

    Journal of Arthroplasty

    (1998)
  • T.S. Johnson et al.

    The effect of displacement control input parameters on tibiofemoral prosthetic knee wear

    Wear

    (2001)
  • M.A. Lafortune et al.

    Three-dimensional kinematics of the human knee during walking

    Journal of Biomechanics

    (1992)
  • P.I. Barnett et al.

    Comparison of wear in a total knee replacement under different kinematic conditions

    Journal of Materials Science: Materials in Medicine

    (2001)
  • P.I. Barnett et al.

    Investigation of wear of knee prostheses in a new displacement/force controlled simulator

    Proceedings Institution Mechanical Engineers. Part H: Journal of Engineering in Medicine

    (2002)
  • D.L. Bartel et al.

    The effect of conformity, thickness, and material on stresses in ultra-high molecular weight components for total joint replacement

    The Journal of Bone and Joint Surgery

    (1986)
  • Furman, B.D., Schmieg, J.J., Bhattacharyya, S., Li, S., 1999. Assessment of backside polyethylene wear in three...
  • G.I. Howling et al.

    Quantitative characterization of polyethylene debris isolated from periprosthetic tissue in early failure knee implants and early and late failure Charnley hip implants

    Journal of Biomedical Materials Research

    (2001)
  • E. Ingham et al.

    Biological reactions to wear debris in total joint replacement

    Proceedings Institution Mechanical Engineers. Part H: Journal of Engineering in Medicine

    (2000)
  • ISO 14243-1, 2002. Implants for surgery—wear of total knee joint prostheses. Part 1: Loading and displacement...
There are more references available in the full text version of this article.

Cited by (285)

  • Understanding the differences in wear testing method standards for total knee replacement

    2022, Journal of the Mechanical Behavior of Biomedical Materials
View all citing articles on Scopus
View full text