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Blood and urine metal ion levels in young and
active patients after Birmingham hip resurfacing
arthroplasty
FOUR-YEAR RESULTS OF A PROSPECTIVE LONGITUDINAL STUDY
J. Daniel, FRCS, Director of Research1; H. Ziaee,
BSc(Hons), Biomedical Scientist1; C. Pradhan, FRCS,
Staff Orthopaedic Surgeon1; P. B. Pynsent, PhD,
Director2; and D. J. W. McMinn, FRCS, Consultant
Orthopaedic Surgeon1
1 The McMinn Centre, 25 Highfield Road, Edgbaston,
Birmingham B15 3DP, UK.
2 Research and Teaching Centre, Royal Orthopaedic
Hospital, Northfield, Birmingham B31 2AP, UK.
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This is a longitudinal study of the daily urinary output
and the concentrations in whole blood of cobalt and
chromium in patients with metal-on-metal resurfacings
over a period of four years.
Twelve-hour urine collections and whole blood specimens
were collected before and periodically after a
Birmingham hip resurfacing in 26 patients. All ion
analyses were carried out using a high-resolution
inductively-coupled plasma mass spectrometer. Clinical
and radiological assessment, hip function scoring and
activity level assessment revealed excellent hip
function.
There was a significant early increase in urinary metal
output, reaching a peak at six months for cobalt and one
year for chromium post-operatively. There was thereafter
a steady decrease in the median urinary output of cobalt
over the following three years, although the differences
are not statistically significant. The mean whole blood
levels of cobalt and chromium also showed a significant
increase between the pre-operative and one-year
post-operative periods. The blood levels then decreased
to a lower level at four years, compared with the
one-year levels. This late reduction was statistically
significant for chromium but not for cobalt.
The effects of systemic metal ion exposure in patients
with metal-on-metal resurfacing arthroplasties continue
to be a matter of concern. The levels in this study
provide a baseline against which the in vivo wear
performance of newer bearings can be compared.
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