Corrosion,
serious tissue reactions and metallosis are all possible side effects for
recipients of the metal-on-metal hip implant. The safety of these devices has
come under serious question with many recipients requiring revision surgery to
remove the harmful devices. The DePuy ASR was recalled in 2010 due to studies showing
it corroded much more quickly than other types of implants, most notably those
made of ceramic and plastic. Once corrosion occurs in the metal hip implant the
tissues surrounding the implant can become inflamed or soft tissue masses,
lesions and necrosis can occur. The femoral heads as well as the acetabular cup
of the DePuy hip implants are constructed of cobalt and chromium. The past few
years have seen serious concerns regarding the metal chromium and cobalt
particles which shave off when the femoral head and acetabular cup rub against
one another during any activity. Once the levels of corrosion reach the unsafe
stage the implant will likely have to be removed during a revision surgery.
Journal of Anthroplasty Study
A
recent study in the Anthroplasty Journal compared the levels of corrosion on
the femoral heads of the metal hip implants with those constructed of
metal-on-polyethylene which implements a synthetic liner between the metal cup
and femoral head. This liner acts as a buffer between the two metal pieces
meaning there is less chance of the small metal ions slivering off and causing
metallosis or metal toxicity in the bloodstream. The metal ions in the
bloodstream can lead to kidney and liver disease or certain types of cancer,
while the metal shards which lodge in surrounding tissues can lead to serious
inflammation, tumors and even bone loss.
The
study findings showed the metal-on-metal implants had significantly higher
corrosion levels, increasing over time. More specifically, nineteen of the
thirty-three femoral heads removed from patients were metal-on-metal, and
almost half of those showed corrosion outside the taper zone. Of the fourteen
femoral heads constructed of metal-on-polyethylene only one showed any level of
corrosion at all. These levels of corrosion were in turn tied to higher numbers
of adverse tissue reactions among the recipients of the metal-on-metal hip implant
leading to necessary revision surgeries.
Recall of the Metal Hip Implant
Although
the DePuy ASR was recalled in 2010, other metal-on-metal hip implants remain in
use, causing medical experts to call for the complete removal of these unsafe
medical devices from the market. An upcoming meeting in June of the FDA’s
orthopedic advisory board will respond to consumer and physician concerns
regarding the metal implants and review the failure rates associated with these
implants. The board will likely also discuss the relative patient risk, the
potential complications, and the procedure for metallosis testing and implant
imaging. At a minimum the board may demand a more rigorous testing procedure
for the metal-on-metal devices based on the data indicating that as many as one
out of eight implants could fail within five years of the surgery. Over 6,000
patients have already pursued product liability claims against several
manufacturers of the metal-on-metal hip implant devices with more expected to
follow.
