Background: Crossfire cross-linked polyethylene is produced
differently from other cross-linked polyethylene materials; a
below-melt-temperature annealing process is used with the goal of avoiding
compromised mechanical properties. The present study was performed to evaluate
retrieved Crossfire acetabular cups to determine whether they had oxidized and
to what extent oxidation might have influenced their clinical performance.
Methods: Eleven acetabular cups were received at retrieval and a
twelfth acetabular cup was received two years post-retrieval over a period of
four years. None were retrieved because of polyethylene wear or fatigue. The
cups had been in vivo from 0.1 to 5.3 years. Each was examined visually,
clinical fatigue damage was rated, and oxidation was measured with use of
Fourier transform infrared spectroscopy.
Results: The cups exhibited oxidation that varied with its location
on the cup: the oxidation value was generally low on the articular surface but
more than an order of magnitude higher value on the rim. Maximum rim oxidation
correlated significantly with the time in vivo (Spearman rho = 0.734, p =
0.010). Oxidation was identified visually by a white band in thin sections on
the rim of seven of the cups and on the articular surface of one of these
seven cups. Six of the seven cups also exhibited clinical fatigue damage.
Eight of the twelve cups exhibited evidence of impingement or dislocation.
Conclusions: Acetabular cups made of Crossfire polyethylene oxidized
to a measurable degree. The oxidation-related reduction of polyethylene
mechanical properties was sufficient to allow the fatigue damage seen in these
Clinical Relevance: The oxidation measured in acetabular cups made
of Crossfire polyethylene makes them susceptible to fatigue after as little as
three years in service.