SYMPOSIA PAPER Published: 01 January 1998

Effect of Gamma-Radiation Induced Oxidation and Crosslinking on the Wear Performance of Ultra-High Molecular Weight Polyethylene (UHMWPE) Acetabular Cups


The effect of gamma-radiation sterilization on the mechanical and physical properties of ultra-high molecular weight polyethylene (UHMWPE) has been studied in depth, but the effect on tribological properties remains a matter of considerable debate and contention. Most of the conclusions about the tribological properties are either hypothetical or based on wear testing that does not simulate the in vivo wear conditions adequately. In this paper, extensive hip simulator data are presented regarding the wear behavior of UHMWPE acetabular cups. The following sterilization treatments are considered: no sterilization, gamma-radiation in air, gamma-radiation in an inert atmosphere and stabilization, and ethylene oxide (EtO) sterilization. Hip simulator testing was conducted in both the anatomical and the inverted anatomical configurations. In the anatomical configuration, the stabilized UHMWPE acetabular cups demonstrated a reduction in wear of about 65% over EtO sterilized acetabular cups and 20% over air-irradiated cups. The unirradiated UHMWPE cups demonstrated the same wear behavior as EtO sterilized cups. In the inverted anatomical configuration, stabilized cups showed a 54% reduction in wear over the EtO sterilized cups. Oxidation studies further showed that air-irradiated UHMWPE had a propensity for increased oxidation levels over time with a peak in the subsurface while stabilized acetabular cups showed consistently lower oxidation levels with accelerated aging. Gel content analysis showed an increase in the insoluble constituents with gamma radiation, indicating an increase in crosslinks. Based on this study, it was concluded that gamma sterilization in an inert environment followed by thermal activation to accelerate free radical decay improves the tribological properties of UHMWPE while controlling any increase in oxidation levels even after accelerated aging.

Author Information

Polineni, VK
Howmedica, Inc., Rutherford, NJ
Wang, A
Howmedica, Inc., Rutherford, NJ
Essner, A
Howmedica, Inc., Rutherford, NJ
Sun, DC
Howmedica, Inc., Rutherford, NJ
Stark, C
Howmedica, Inc., Rutherford, NJ
Dumbleton, JH
Howmedica, Inc., Rutherford, NJ
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Developed by Committee: F04
Pages: 95–108
DOI: 10.1520/STP11913S
ISBN-EB: 978-0-8031-5379-0
ISBN-13: 978-0-8031-2482-0