Abstract
Background: There is a paucity of published literature with regard to metal ion levels following bilateral hip resurfacings.
Method: Recent research has identified femoral component size and acetabular cup anteversion and inclination as important variables involved in metal ion release into the blood. We compared 13 patients with bilateral joints resurfaced using the ASR and 11 patients with bilateral BHRs to those with unilateral joints of similar size and cup inclinations/anteversions. Patients were excluded if the last procedure was within 12 months of blood sampling and if they had other metallic implants. Analysis of standing radiographs to determine cup orientation was carried out using EBRA software. Blood samples were analysed using ICPMS.
Results: Median whole blood Cr and Co values were higher in the BHR bilateral group when compared to the unilateral BHR group by a factor of 1.12 and 1.24 respectively. (5.17 vs 4.59 for Cr, 2.40 vs 1.93 for Co). The difference was significant for Co (p=0.030) but not for Cr (p=0.136). For the large ASR joints (53mm), median Cr and Co values were higher in the bilateral group by a factor of 1.5 and 1.85 respectively. (4.55 vs 2.97 (Cr) 2.83 vs 1.53 (Co)). The difference was significant for both Cr (p=0.001) and Co (p=0.022). For the small ASR joints (< 53mm), median Cr Co values were higher in the bilateral group by a factor of 1.95 and 2.30 respectively. (8.29 vs 4.25 (Cr), 6.78 vs 2.94 (Co)) (p=0.019 Co) (p=0.007 Co).
Conclusion: Metal ion concentrations are significantly greater in patients with bilateral resurfacings. The Cr Co concentrations observed in our patients with bilateral small ASR joints are double those in the published literature on bilateral 28mm metal on metal(MoM) joints implying that the lubrication achieved by small ASRs is sub optimal.
Correspondence should be addressed to BHS c/o BOA, at the Royal College of Surgeons, 35–43 Lincoln’s Inn Fields, London, WC2A 3PE, England.
