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Study Sees Elevated Metal Ion Levels in Blood of Metal-on-Metal Hip Implant Recipients

Mar 26, 2012 | Parker Waichman LLP

Another study is raising questions about the safety of metal-on-metal hip implants.  According to the research, which compared two sizes of metal-on-metal hip implants with metal-on- polyethylene devices,  patients with all-metal hip replacements exhibited significantly higher levels of metal ions in their blood in the years following their surgery.  Those with large metal-on-metal-hip implants (36 mm) also experienced increasing ion levels at five years post-op, while those in patients with small femoral heads (28 mm) eventually leveled off.

The study was presented by C. Anderson Engh Jr., MD at the American Academy of Orthopaedic Surgeons 2012 Annual Meeting, in San Francisco.  Of 120 total hip replacement patients enrolled, 105 patients were eligible for the study at the time of their surgery.  Blood samples were obtained from the patients preoperatively and postoperatively at 6 months, 1 year, 2 years, 3 years and 5 years.

At 5-years post-op, both groups of metal-on-metal hip implant patients showed significantly higher levels of chromium and cobalt ions than those in the polyethylene-on-metal group.  Six months after surgery, one patient in the 36-mm group had serum or erythrocyte ion levels greater than 7 parts per billion.  At 5-year follow-up, four more patients in the group exhibited ion levels at this level.  This increase overtime was not seen in the 28 mm metal-on-metal hip implant group, as metal ion levels appeared to plateau.

“These median ion levels are similar to what we see in other studies,” Engh said. “The cobalt levels are well commmrrelated. The surprising thing was that the MoMs (metal-on-metal) were not performing as well both anecdotally — with adverse tissue reaction, osteolysis and the higher ion levels — and also the 36 mm having an increasing ion level with time.”

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