• Michel J Le Duff, Alicia J Johnson, and Harlan C Amstutz.
• Joint Replacement Institute, St Vincent Medical Centre, Los Angeles, California - USA.
• Hip Int. 2014 Jul 1; 24 (4): 327-32.

BackgroundElevated cobalt and chromium ion concentrations have been associated with the use of metal-on-metal bearings in hip arthroplasty. The use of a differential hardness bearing may reduce metal particle release. The aim of our study was to compare circulating cobalt (Co) and chromium (Cr) ion levels between patients treated with a standard all 'as-cast' heat treated bearing and a differential hardness bearing.Materials And MethodsOne hundred and thirty-two patients implanted with unilateral hip resurfacing arthroplasties and having had blood metal ion studies performed between one and six years after surgery were retrospectively selected. There were 73 patients in the standard all 'as cast' heat treated bearing group (group 1) and 59 in the differential hardness bearing group (group 2).ResultsClinical and quality of life scores were comparable between groups. The median Co in group 1 was 1.01 µg/L and 1.23 µg/L in group 2 (p = 0.0566). The median Cr in group 1 was 1.60 µg/L and 1.34 µg/L in group 2 (p = 0.0505).ConclusionCompared with conventional heat-treated CoCr bearings, differential hardness metal-on metal bearings do not confirm in vivo the hopes of a substantial reduction in circulating metal ions concentrations suggested by in vitro wear studies.

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