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Cobalt ion release after total knee arthroplasty (TKA) higher than after hip resurfacing (HR) at one year follow up

In the absence of harmonized guidance to assess ion release in total knee replacement, a French group undertook a retrospective comparison of the blood ion level of hip resurfacing patients and TKA patients.

TKA systems are known to generate passive corrosion and therefore to release metal ions.

This retrospective case-control single-centre study of 195 cases by Lukas et al., analysed blood levels of Co and Cr ions from 132 patients who underwent hip resurfacing (single device) in 2018 and 63 patients who received total knee arthroplasty (single device) at a minimum follow-up of one year. Blood levels were tested pre-operatively and post-operatively at 6 and 12 months. Hip resurfacing patients received a MoM resurfacing for primary hip osteoarthritis, while the Total Knee replacement patients as a control group received a PS knee.

The relationship between ion release and the change in clinical outcome scores (including Harris Hip score and Oxford Knee score), BMI, sex, physical activity, implant size and inclination of the acetabular implant (for hip patients only) was analysed and mixed linear models were used to assess changes ion blood levels over time.

Results

  • A correlation was found between being female in the HR group and increased levels of Cr in the blood.
  • Greater than 50° acetabular inclination was significantly related to increased Cr release at 12-month follow up in the HR group.

Co Levels

  • Significantly higher at six months post-op in the HR group ([Co] = 0.87 ug/L) in comparison to the TKA group ([Co] = 0.67 ug/L)
  • A trend which was reversed at the 12 month follow up when the TKA group were higher ([Co] = 1.41 ug/L) in comparison with the HR group ([Co] = 1.20 ug/L).

Cr levels

  • Comparatively the Cr levels were significantly higher preoperatively in the HR group
  • No significant difference at the six or 12-month follow ups.

The study concludes that cobalt ion release after total knee arthroplasty is higher than after hip resurfacing at one year follow up and suggests that ion release from arthroplasty implants is due to bearing wear but also to passive corrosion or scratching. The authors recommend monitoring the concentration of metal ions in the blood if the risk factors for elevated metal ion levels are present.

 

📚 Reference: Lukas S, Martinot P, Putman S, et al. Metal ion release after hip resurfacing arthroplasty and knee arthroplasty: a retrospective study of one hundred ninety-five cases [published online ahead of print, 2023 Aug 31]. Int Orthop. 2023;10.1007/s00264-023-05915-6. doi:10.1007/s00264-023-05915-6