With metal-on-metal ("MoM") hip arthroplasty systems grappling
with several critical issues, the US Food and Drug Administration
("FDA") asked for opinion regarding the risks associated with the
device from its advisory panel (Orthopaedic and Rehabilitation
Devices Panel) last week. The panel dealt with issues such as
failure rates and modes, metal ion testing, imaging methods, local
and systemic complications, patient risk factors and considerations
for follow-up after surgery.
As per reports published in the Associated Press, experts from
the 18- member panel were not in favor of using metal-on-metal hip
implants. Although the FDA did not consider banning the device from
the market, most panelists opined that only in a few cases they
would recommend implanting such devices.
The panelists suggested that patients with pain and other
symptoms should get regular X-rays and blood testing for their
metal levels. However, the accuracy of blood tests and difficulties
in interpreting the results remain a major challenge as standard
diagnostic kits are not available to test for chromium and other
metals. Even patients without any complaints should go for X-rays
annually to monitor their implants.
The agency has also asked manufacturers of MoM total hip
replacement ("THR") systems like
Johnson & Johnson
) and Biomet to conduct long-term, follow-up studies of more than
100 metal-on-metal hips on the US market.
Concerns about MoM Hip Implants
More than 400,000 hip arthroplasty procedures are performed in
the US annually. The FDA had earlier noted that MoM replacements
have certain specific risks besides the general risks of hip
implant systems. Since the metal ball and the metal cup slide
against each other during walking or running, some tiny metal
particles may wear off of the device and enter into the space
around the implant. Moreover, metal ions from the metal implants or
from the metal particles may even get into the bloodstream.
Despite several precautions undertaken by orthopedic surgeons to
optimize the way in which the ball and socket rub against each
other so that fewer wear particles are produced, there is no way to
fully avoid the production of metal particles. The reaction to
these possible situations is not uniform among the patient
population. In some cases, it has been observed that high levels of
metal ions in the bloodstream of the patients may adversely affect
other parts of the body including the heart, nervous system, and
the thyroid gland.
In the US, two significant device recalls have taken place for
MoM THR systems. The first of which was the voluntary recall (class
II) of Durom Acetabular Component ("Durom Cup") by Zimmer Holdings
in 2008 because of inadequate instructions for use. This was
followed by the 2010 device recall of ASR total hip systems by
DePuy, a unit of Johnson & Johnson, due to
higher-than-anticipated revision rates noted from outside-the-US
joint registries. While the Durom device is available in the US
with more detailed surgical technique instructions and a surgeon
training program, the ASR did not return to the market.
Measures undertaken outside the US
In February 2012, the Medicines and Healthcare products
Regulatory Agency ("MHRA") - the UK government agency which is
responsible for ensuring that medicines and medical devices work
and are acceptably safe- increased scrutiny of patients with MoM
implant. The agency asked the surgeons that patients with MoM hip
replacements with head diameters of 36 mm or more should be
monitored annually for the life of the hip replacement. This was
done to detect any complication at the earliest so that more
complex surgeries could be avoided. The previous advice, issued in
April 2010, required monitoring for a minimum of five years after
This was followed by Health Canada issuing a public health
communication to orthopedic surgeons and patients about potential
health risks associated with MoM hip implants in May 2012. The
agency noted that female patients, patients with increased activity
levels, patients who are severely overweight and those with
implants in both hips experienced increased risk of adverse local
We believe that the various post-market studies currently
underway should ultimately benefit the wide patient population. We
also doubt whether an extreme step like an overall ban on the use
of this technology is good for patients across the board because
these implants could come of help to some patients.
Favorable data from
Smith & Nephew
) on a new study for its Birmingham Hip Resurfacing ("BHR") system
announced earlier this year provides a lease of hope for this
technology. The study, carried out at the request of the FDA,
followed the progress of the first 400 BHR patients in the UK. It
was observed that after 10 years, 99% were either satisfied or
extremely satisfied with their BHR procedure.
Given the mixed reviews, additional and in-depth study on the
use of MoM technology is the call of the hour. Meanwhile, MedTech
firms in the replacement niche have to counter yet another looming
headwind in an already tight playing field.
We have a Neutral recommendation for JNJ, Zimmer and Smith &
Nephew over the long term.
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