Metal Ions – High Activity, High Wear?
Metal Ion Levels
Chromium, Cobalt and Molybdenum are of course normal dietary constituents and indeed essential dietary constituents. All of us, therefore, have a certain level of these metal ions measurable in our blood. We were interested to see if very active patients with metal on metal bearings in situ had any elevation of their blood metal ions compared with another group of patients with metal on metal bearings who had a low activity level. We selected two groups of patients, one group with a very high activity level who all played sport following a successful Birmingham Hip Resurfacing and a second group of patients who were elderly and inactive following a historical metal on metal total hip replacement performed more than 20 years before.
We worked with the trace metals laboratory at AEA Harwell on this project and we measured mineral digested whole blood Cobalt, Chromium and Molybdenum levels using high-resolution induction coupled plasma mass-spectrometry. The results of these measurements are shown and when comparison was done using the t-test, no significant difference in Cobalt, Chromium or Molybdenum was seen between the high activity group and the low activity group.
The conclusion from these results is that there is no correlation between the activity level and wear of a metal metal bearing and is strong supportive evidence that thick film lubrication occurs in these metal on metal bearings. This is totally different to a metal polyethylene bearing where the wear of the bearing is related to the number of walking cycles. Therefore, high activity on a metal polyethylene articulation leads to high wear and osteolysis.
© 2007 Smith & Nephew