Simple mathematical and computational wear model for ultra-high-molecular-weight polyethylene total hip replacements

K H S Chan,F Wong,L Chow,R W Blake,T Pearce,S Wu,J Li

doi:10.1080/11762320701523679

Abstract

Ultra-high-molecular-weight polyethylene is an important constituent of hip implants. Surgical revisions are required because of implant loosening and osteolysis destruction or resorption of bone tissue. We develop a mathematical and a computational model to determine implant life defined as the time when 20% of the implants operating at a given wear rate is revised based on wear rates and apply them to the data of Sochart Clin Orthop Relat Res, 363:135--50, 1999. No significant difference was found between mathematical and computational model predictions 14.8 and 14.7 years, respectively from the actual value of 15.0 ± 3.9 years \bar{X} ± 2SE; P > 0.05. We find that an increase in cross-linking does not decrease implant life greatly. However, a large decrease in implant life occurs with an increase in surface roughness, cycles per year and body weight or a decrease in contact stress and femoral head radius.

Highlights

Ultra-high-molecular-weight polyethylene (UHMWPE) is used for total joint arthroplasty (Wang et al 1995, 1998; Scholes et al 2000; Wang 2001; Endo et al 2002; Lewis et al 2003)
Evidence suggests that it is linked to osteolysis
Research has focused on wear rates of UHMWPE by different material parameters

Summary

Introduction

Ultra-high-molecular-weight polyethylene (UHMWPE) is used for total joint arthroplasty (Wang et al 1995, 1998; Scholes et al 2000; Wang 2001; Endo et al 2002; Lewis et al 2003). Research has focused on wear rates of UHMWPE by different material parameters (e.g. molecular weight between cross-links [Wang 2001], femoral head roughness [Wang et al 1998], coefficient of friction, contact stress [Wang et al 2001], tensile toughness, crystallinity and protein concentration [Lewis et al 2003]). As far as we are aware, no mathematical or computational relationships between implant revisions and wear rates have been developed.

Results

Conclusion