The Great Ion Debate: Is Metal or Plastic the Worse Offender?

And the great ion debate continues.

A randomized study concludes that metal-on-metal bearings produce similar levels of ions as metal-on-polyethylene bearings.

Researchers with Ottawa Hospital in Ontario, Canada, randomly assigned 50 patients who underwent primary total hip arthroplasty (THA) to receive either a metal-on-metal (MoM) bearing with an all cobalt-chromium shell or a metal-on-polyethylene (MoP) bearing with a titanium shell. Final analysis included 24 patients in the MoM group and 23 patients in the MoP cohort. Both groups had a mean age of 60.2 years. Median head size in the MoM group was 46 millimeters vs. 32 millimeters in the MoP group. Median acetabular component sizes for the groups were 54 millimeters and 52 millimeters, respectively.

Results showed significantly higher levels of median serum chromium and cobalt in the MoM group at both one year and two years. However, researchers found serum titanium levels were similar between the MoM and MoP groups at one year and significantly higher in the MoP group at two years. Chromium, cobalt and titanium serum levels increased significantly from baseline and remained consistent at two years in the MoM group, with the exception of chromium which had a significant increase from one year to two years, according to the data. In comparison, serum chromium levels remained unchanged from baseline to two years and serum cobalt and titanium increased significantly at one year in the MoP group.

According to multiple regression analysis, head size was a significant predictor of chromium and cobalt levels.