Metal From Hip Implants Passed on to Babies

Some moms might pass more than genetics to their newborns. Doctors found three babies born to women with hip implants had high levels of chromium and cobalt in their umbilical cord blood — metals that had worn off the implants.

The results show an association between levels of cobalt and chromium — components of metal implants — in mothers and their babies at the time of delivery.

The finding was only for women with so-called "metal-on-metal" hip implants, in which both the ball of the joint and the surface of the socket are made of metal. The charged form of the cobalt and chromium, called ions, get released as a result of wear and corrosion as the metal parts rub against one another.

The researchers stress that they aren't sure if these metals have detrimental effects for either the mother or her offspring. And the study involved only a few participants, so more research is needed to confirm the findings.

"We don't know whether metal ions pose any health risks for pregnant women and their babies," said study researcher Dr. Joshua Jacobs, an orthopedic surgeon at Rush University Medical Center in Chicago. "But as metal-on-metal implants increase in popularity and use, especially among young, active patients, women of child-bearing age and their doctors need to be aware of these findings when considering options for hip replacements."

The study will be presented today at the 2010 Annual Meeting of the American Academy of Orthopaedic Surgeons in New Orleans.

Jacobs and his colleagues evaluated three women who had metal-on-metal hip implants and gave birth two to six years after their surgeries.

Maternal and umbilical cord blood was obtained at the time of delivery and tested for blood serum concentrations of titanium, nickel, cobalt and chromium using a highly sensitive technique that can detect trace amounts of metals in biological samples.

They found mothers with metal-on-metal implants and their newborns had significantly higher levels of chromium and cobalt compared with a control group of seven women and their babies who were also tested at the time of delivery.

In addition, levels of these metals in the blood of mothers with implants correlated with the levels found in the umbilical cords. Cobalt levels in newborns were about half that in the mothers' blood, while chromium levels were about 15 percent of the mothers' chromium levels. In the control group, no correlation existed.

The lower levels in the umbilical cords indicated that the placenta provided at least some barrier to the transfer of metal ions from mother to fetus, but not a complete barrier, Jacobs said.

Levels of titanium and nickel showed no significant difference between the two groups.

It is unknown whether metal ions in the bloodstream — for pregnant mothers, developing fetuses or newborns — pose any significant health concern. Medical device companies are working to improve the wear and corrosion properties of metal implants to reduce the release of metal ions, according to Jacobs.

"Any advancements in this area will directly benefit patients," he said.

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