The value of serial metal ion levels in following up patients with metal-on-metal hip arthroplasty.

BACKGROUND: The sensitivity of cobalt (Co) and chromium (Cr) ion-levels in detecting poorly performing metal-on-metal hip implants is low. This study proposes that serial changes in ion-levels are a more accurate marker of arthroplasties at risk.

METHODS: Serial metal ion-levels and implant data of 285 patients with ASR resurfacing or replacement were studied. Patient and implant characteristics were analysed using univariate and multivariate analyses.

RESULTS: 111 (39%) had revision surgery. Time since index surgery (p<0.001), acetabular inclination (p<0.001), their interaction (p<0.001) and femoral head size (p = 0.01) were significant variables. Head size (≤51 mm) had lower Co and Cr levels (p = 0.01). Cr/Co showed marginal decrease over time in the unrevised group and no decrease prerevision.

CONCLUSIONS: Repeated measurement of ion-levels were higher in the revision group suggesting that serial measurements rather than absolute values may have a role to play in predicting implant failure.