Are Metal-on-Metal hip implants safe?
aching bones – once,
there was little to do
but accept problems
like these as part
o f a g e i n g . B u t
n o w , m o d e r n
hip implants can
help give people
their mobility back.
M e t a l - o n - M e t a l
joint implants, one specific category of
implants, may solve many dysfunctions
related to the hip. But, but do they come
The European Commission’s Scientific
Committee on Emerging and Newly
Identified Health Risks (SCENIHR) responds
to this question in its Opinion on “The
safety of Metal-on-Metal (MoM) joint
replacements with a particular focus on
hip implants”, the main points of which are
summarised in this fact sheet.
WHaT aRE METal-ON-METal HIp
Hip replacements can be total or partial,
replacing all or only one of the two
components of the hip joint – the ball and
socket – that should glide together smoothly
to make movement easy.
In a total hip replacement, the femoral head
(the top of the thigh bone) and the damaged
acetabulum (the socket) are removed and
replaced with metal, plastic or ceramic
In hip resurfacing arthroplasty, the femoral
head is not removed. The damaged area
is trimmed and fitted with a smooth cap.
Damaged bone and cartilage within the
socket, however, are removed and replaced,
like in total hip replacements.
In Metal-on-Metal hip implants, the
replacement components in both the ball and
the socket are made of metal. This type of
implant can be used for both total and partial
hip replacement surgery.
WHy uSE METal?
used in younger patients to save them
having to undergo revision operations later
to replace less durable plastic parts. Metal
implant components tend to be larger as
well, making them more durable and less
likely to dislocate.
WHaT aRE THE CONCERNS aBOuT
When two components, as in an implant,
continually rub against each other, there may
be some resulting debris. In Metal-on-Metal
hip implants, tiny metal particles may wear
off due to friction and build up over time
around the implant and even end up in blood
Most patients who have Metal-on-Metal
implants have no adverse effects, but some
patients experience symptoms around
the hip, like swelling. A few others report
problems located elsewhere than the hip
area that may possibly be related to the
release of metallic substances.
WHaT aRE SCENIHR’S CONCluSIONS
The SCENIHR concludes that large-head
(large diameter) Metal-on-Metal hip
implants, in particular, pose the highest risk
of provoking undesirable reactions.
Because of the potential health risk posed by
Metal-on-Metal hip implants, the decision to
use them should be made on an individual
basis, weighing the pros and cons and
considering relevant factors such as
age, gender, body size, physical fitness
All types of Metal-on-Metal implants
should be avoided by high-risk patients
including females of childbearing age,
small-boned females and patients who
are allergic to the relevant metals.
If Metal-on-Metal implants are judged
to best fit a patient’s needs, the
surgery should only be performed by a
very experienced surgeon to minimize
For post-operative care, the SCENIHR
endorses the strategy outlined in the
European Consensus Statement, which
recommends that all patients with
implants have regular radiographic
and clinical check-ups. In particular,
routine checks should be conducted for
any metal ions from large-head Metal-
on-Metal total hip replacements, and
patients who have had hip resurfacing
arthroplasty should have regular
check-ups at least during the first
This opinion is available at:
Opinion of the independent Scientific
Committee on Emerging and Newly
Identified Health Risks (SCENIHR):
“The safety of Metal-on-Metal joint
replacements with a particular focus
on hip implants".