A new study involving metal-on-metal hip implants found that recipients of the devices exhibited high levels of metal ions in their blood in the years after surgery, compared to patients fitted with those made with a polyethylene liner. The study also found that while metal ion levels plateaued in patients smaller all-metal hip implants (28 mm femoral heads) levels continued to increase in patients with larger devices (36 mm)
According to a report from OrthoSuperSite.com, the study was presented by C. Anderson Engh Jr., MD at the American Academy of Orthopaedic Surgeons 2012 Annual Meeting, in San Francisco. Dr. Engh and his team compared patients who received a metal-on-polyethylene total hip replacement with two groups of all-metal hip implant recipients, 28 mm and 36 mm. Blood samples were obtained from the patients preoperatively and postoperatively at 6 months, 1 year, 2 years, 3 years and 5 years. Of 120 people enrolled, 105 patients were eligible for the study at the time of their surgery.
At five year follow-up, metal-on-polyethylene patients had significantly lower chromium and cobalt ion levels compared to either of the metal-on-metal groups. However, while the levels of ions seen in those fitted with the smaller all-metal hip implant leveled off, those with the 36 mm femoral head experienced increasing levels over time, according to OrthoSuperSite.com. Six months after sugary, 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. None of those in the 28 mm metal-on-metal hip implant group exhibited these findings.
“These median ion levels are similar to what we see in other studies,” Engh said, according to OrthoSuperSite.com. “The cobalt levels are well correlated. 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.”
This is just the latest study to cast doubts on the safety of metal-on-metal hip implants. Concerns about the devices started to mount in 2010, when DePuy Orthopaedics issued a recall of its ASR hip implants, following findings that they were failing in about 12 percent of patients within five years. Realistically, a hip implant should last around 10-15 years. The recall has sparked thousands of lawsuits, most of which are pending in a multidistrict litigation in federal court in Ohio.
Late last month, the British Medical Journal revealed that metal-on-metal hip implant manufacturers were aware of mounting evidence linking metal-on-metal hip replacement devices to serious, long-term health consequences, but for years failed to warn the public about these dangers. Earlier this month, The Lancet published a study conducted by University of Bristol researchers who found that people with metal-on-metal hip implants were twice as likely to experience early failure of their device compared to those fitted with other types of implants. The authors of the study asserted the devices should no longer be used.
Regulators here and abroad have also been extremely concerned about the devices. Last May, the U.S. Food & Drug Administration (FDA) directed 21 companies that market all-metal hip replacement devices to conduct post-market studies of their products to determine if they were shedding dangerous amounts of metallic debris in patients In the U.K., n the U.K., the Medicines and Healthcare Products Regulatory Agency (MHRA) announced that blood tests should be conducted yearly to check cobalt and chromium blood levels in some all-metal hip implant recipients, those with bearings of 36 mm or above, as well as MRIs for any patient who does exhibit high metal ion levels.
Since the DePuy ASR hip implant recall, other manufacturers have been named in lawsuits over their metal-on-metal hip replacement devices. In February, a multidistrict litigation was established in the U.S. District Court for the Northern District of Georgia for lawsuits involving the all-metal Wright Conserve Hip Replacement System. Claims involving a metal-on-metal version of DePuy’s Pinnacle hip implant have been consolidated in a multidistrict litigation in Texas.