Enhanced Hip Tribological and Mechanical Properties of AOX™ UHMWPE Blend

Authors and Affiliations:

Elizabeth Hippensteel and Bharat Patel, PhD

DePuy Synthes Joint Reconstruction, Warsaw, IN USA

Keywords: total hip arthroplasty, hip, wear simulation, AOX™, antioxidant

Abstract:

Introduction

The application of Pentaerythritol tetrakis (3-[3,5-di tertiary butyl-4-hydroxyphenyl] propionate (PBHP) antioxidant Ultrahigh Molecular Weight Polyethylene (UHMWPE) blends (AOX™ Antioxidant Polyethylene) in total hip arthroplasty offers potential advantages including long-term oxidative stability of the implant, improved wear properties and potential for improved mechanical properties. This study quantified wear of AOX™ Antioxidant Polyethylene material in a joint simulator and its mechanical attributes under accelerated aging conditions.

Methods

Two acetabular liner groups (n=6 for each + 4 each loaded soak controls) were evaluated in this study. The control liners (GUR 1050 UHMWPE cross-linked at 5.0Mrad and re-melted) and AOX™ Liners were articulated against CoCrMo femoral heads. Testing was conducted on an AMTI ADL hip simulator with load soak controls for 6.0 million cycles (MC) in bovine serum and gravimetric wear was calculated. A student’s t-test was used to analyze differences in wear rates between sample groups. Accelerated aging for the AOX™ Antioxidant Polyethylene was performed under ASTM F2003 protocol, wherein the material was aged at 70^oC under O₂ at 5 atm. for 14 days. While we studied 14 days, we also extended the aging period to 28 and 40 days.

Results

The mean wear rate (mg/MC±95% CI) was 10.8±2.4 and 6.4±0.7 for the control and AOX™ Liners, respectively. The results conclude that the mean wear rate of the AOX™ Liners was not statistically significantly greater (p > 0.99) than the mean wear rate of the control liners. Data from the extended aging studies indicate mechanical properties such as tensile, yield and impact strength remain relatively constant after 40 days of aging according to ASTM F2003.

Conclusions

This study evaluated the gravimetric wear of an AOX™ Acetabular Liner as compared to a control UHMWPE. The wear rate of the AOX™ Liners was not statistically significantly greater than the control UHMWPE. Mechanical properties remain relatively constant with aging indicating material stability. The data provides a baseline for understanding AOX™ Acetabular Liners for use in hip bearings with increased tribological demands as well as enhanced mechanical properties.

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