The study was published in The Journal of Bone & Joint Surgery (3/14) and investigated the levels of metal ions in patients who received either 36-mm or 28-mm metal-on-metal implants, or a metal-on-polyethylene hip implant. In the background to the study, the authors noted that the US Food and Drug Administration (FDA) had requested post-market surveillance data on patients who received metal-on-metal hip devices.
To conduct the study, researchers examined 105 patients who were randomly assigned to the different surface options. Evaluations, including analysis of the metal ion levels in the patients’ erythrocytes, serum and whole blood, were conducted on a regular basis. Researchers found that the cobalt and chromium ion levels in all blood sample points were “significantly lower” in the metal-on-polyethylene group than in the two metal-on-metal groups, with the only exception being the level of chromium in erythrocytes. Furthermore, researchers found that cobalt in serum and erythrocytes increased significantly from two years to five years in the group that had the 36-mm metal-on-metal implant, but not in the group that received the 28-mm metal-on-metal implant.
Meanwhile, after five years, there were five patients who received 36-mm metal-on-metal implants who had cobalt or chromium levels of greater than seven ppb.
Researchers also noted that one patient who received the 36-mm metal-on-metal device underwent revision surgery due to an adverse tissue reaction to the hip replacement.
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Other problems reportedly linked to metal-on-metal hip devices include joint dislocation, slippage, soft tissue damage and/or infection.
Due to concerns about the risks of metal-on-metal hip replacement implants, on May 6, 2011, the FDA instructed the companies who make such hip replacement systems to conduct post-market surveillance studies of their devices.