Oxidised zirconium versus cobalt alloy bearing surfaces in total knee arthroplasty

Aims

We sought to establish whether an oxidised zirconium (OxZr) femoral component causes less loss of polyethylene volume than a cobalt alloy (CoCr) femoral component in total knee arthroplasty.

Materials and Methods

A total of 20 retrieved tibial inserts that had articulated with OxZr components were matched with 20 inserts from CoCr articulations for patient age, body mass index, length of implantation, and revision diagnosis. Changes in dimensions of the articular surfaces were compared with those of pristine inserts using laser scanning. The differences in volume between the retrieved and pristine surfaces of the two groups were calculated and compared.

Results

The loss of polyethylene volume was 122 mm³ (standard deviation (sd) 87) in the OxZr group and 170 mm³ (sd 96) in the CoCr group (p = 0.033). The volume loss in the OxZr group was also lower in the medial (72 mm³ (sd 67) versus 92 mm³ (sd 60); p = 0.096) and lateral (49 mm³ (sd 36) versus 79 mm³ (sd 61); p = 0.096) compartments separately, but these differences were not significant.

Conclusion

Our results corroborate earlier findings from in vitro testing and visual retrieval analysis which suggest that polyethylene volume loss is lower with OxZr femoral components. Since both OxZr and CoCr are hard surfaces that would be expected to create comparable amounts of polyethylene creep, the differences in volume loss may reflect differences in the in vivo wear of these inserts.