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Leonard R. Walter MBBS(Syd), FRACS,
FAOrthA, Ed Marel MBBS(Syd), FRCS Ed (Orth),
FRACS, FAOrthAa,
Richard Harbury MBBS(Syd), FRACS, FAOrthAa
and Jenny Wearne RN
aPeninsula Orthopaedics Research
Institute, DEE WHY NSW 2099, Australia
Received 28 November 2006;
accepted 7 July 2007
Abstract
The most appropriate blood fraction for the
measurement of metal ions in patients with
metal-on-metal implants is controversial. We
compared chromium (Cr) and cobalt (Co) ion
levels in 29 patients after unilateral hip
resurfacing with a size 54-mm femoral Birmingham
Hip Resurfacing Prosthesis (Smith and Nephew,
London, UK). All had well-functioning
arthroplasties between 5 and 59 months after
implantation. Ion levels were measured in serum,
plasma, red cells, and whole blood in each
patient. Our results indicate that only very
minor amounts of Cr and Co are associated with
red blood cells, with most being associated with
serum/plasma. Previous studies using corrosion
to produce the ion load have showed a
predominance of Cr in the red blood cells. They
have also shown that the cellular uptake of Cr
is an indicator of its valence. This difference
in distribution with our results is indirect
evidence that the Cr released from wear of this
implant is probably in the more benign trivalent
form. It also suggests that most of the metal
loss from a normally wearing bearing may be from
wear rather than corrosion. If blood is to be
used to assess rates of wear and systemic ion
levels, then serum gives a better reflection of
the true levels than red blood cells.
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