Hip replacement patients with
metal-on-metal (MoM) implants (both
the socket and hip ball are metal)
pass metal ions to their infants
during pregnancy, according to a new
study presented today at the 2010
Annual Meeting of the

American Academy of Orthopaedic
Surgeons (AAOS). Data showed
there is a correlation between
cobalt and chromium levels in the
mother and those in her infant at
the time of delivery.

“Although the affects of metal
ions in maternal and fetal subjects
are unknown, the fact that the
placenta is not a complete barrier
to the transport of these metals is
noteworthy,” said Joshua J. Jacobs,
MD, Professor and Chairman of Orthopaedic Surgery at Rush
University Medical Center in
Chicago. “As metal-on-metal implants
increase in popularity and use,
especially among young, active
patients, women of child-bearing age
and their doctors should be aware of
these findings when considering
their hip replacement implant
options.”

Researchers evaluated three
patients who had either a unilateral
(only on one hip) MoM primary total
hip arthroplasty or unilateral MoM
hip resurfacing joint replacement
and no other metal implant in the
body. The implant group’s metal ion
levels were compared within the
group, between mothers and their
infants, and to those of a Control
Group comprising seven women of
child-bearing age (mean age of about
32 years) who did not have any metal
implants and their infants.

For all subjects, 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 inductively coupled
plasma mass spectrometry (ICP-MS), a
highly sensitive technique that can
detect trace amounts of metals in
biological samples.

The data found:

• Mothers with MoM implants
  and their offspring had elevated
  Chromium and cobalt levels
  compared to the cohort without
  metal implants.
• A correlation existed
  between maternal and infant
  cobalt and chromium levels in
  the Implant Group, while the
  Control Group showed no
  correlation.
• Offspring of women with MoM
  implants had about half the
  levels of cobalt in their
  bloodstream as their mothers and
  approximately 15 percent of
  their mother’s chromium levels,
  while there was no significant
  difference among ion levels
  between mothers and infants in
  the Control Group.
• There was no statistically
  significant differences in
  levels of titanium or nickel
  among any of the cohorts.

Dr. Jacobs noted that because the
cobalt and chromium levels of the
infants did not increase to those of
their mothers, the data suggests the
placenta does modulate the transfer
of metal ions to the fetus.

“The next step is to find out
what, if any affect metal ions have
on fetal or infant development,” he
said. “The best way to do that would
be through the establishment of a

national joint registry by which
clinicians could input and access
long-term data.”

He added that, in the meantime,
medical device companies are
feverishly working to develop new
technologies that will reduce the
release of ions through improvements
in wear and corrosion properties of
metal implants. “Any advancements in
this area will directly benefit
patients,” he said.