What is a MOM hip replacement?
Metal-on-metal (MOM) hip replacements consist of a femoral metal
ball and acetabular socket – as opposed to the traditional metal
ball and plastic socket replacement – and became popular in the
1990’s.
The metal components of the MOM hips are made of a
cobalt-chromium alloy; inert metals that are unlikely to cause any
reaction within the body.
These metal hips have been implanted into a million patients
worldwide, but with the emerging problems coming to light over
recent months, confidence in the products has fallen and the number
of patients and orthopaedic surgeons using them has reduced to
virtually zero today.
Why has the MHRA launched an investigation into MOM hip
replacements?
In September 2010, the Medicines and Healthcare products
Regulatory Agency (MHRA) put out an alert regarding the safety of
MOM hips, and those manufactured by DePuy were recalled following
high failure rates and problems.
The MHRA issued patient advice, recommending that those who had
undergone a MOM hip replacement – whether they had symptoms of
joint failure or not - should revisit their original orthopaedic
surgeon to have tests on the implant and discuss the potential need
for revision surgery. They go on to specify that MOM hips should be
reviewed annually, and estimates suggest that 50% of those with a
MOM hip replacement will need revision surgery within 5 years of
implantation.
Why have some of the MOM hip replacements been recalled?
Both components (ball and socket) of the hip replacement come
into direct contact and rub together, releasing nanoparticles of
cobalt-chromium into the blood stream in large quantities. This is
often in excess of safe limits, and concerns focus around one of
the agents being carcinogenic, and subsequent inflammatory problems
in some patients.
What are the risks of an MOM hip replacement?
There are three problems associated with MOM hip
replacements:
- Inflammation due to metal particles
The release of cobalt-chromium nanoparticles stimulate an
aggressive inflammatory response in some patients, resulting in
tissue damage around the joint
- Accelerated wearing
Data indicates that
in some patients, the MOM joints are more prone to accelerated
wearing
- Incorrect surgical positioning
Again, data suggests that incorrect positioning of the metal socket
component can have a significant negative impact on the failure
rate
Many patients experience ‘silent’ symptoms - they feel well and
have no joint pain. Despite this, recommendations are regular
monitoring to ensure prompt identification of a potential
failure.
Correcting the MOM hip replacement issues
The London Clinic leads the way in assessments and revision
surgery with a multi-disciplinary expert team. Despite never
implanting the recalled DePuy products, the Clinic offers a
specialised and expert assessment of any patient with a MOM hip
replacement. This includes measurement of the cobalt-chromium
nanoparticle levels within the blood, metal artefact reduction
sequence (MARS) MRI to investigate soft tissue damage around the
implant, and 3D CT scanning to determine the exact position of the
hip. Based on the outcome of these tests, the Clinic offers a
number of monitoring and treatment options, including detailed
surgical planning of a revision operation if necessary.
Mr Alister Hart, Consultant Orthopaedic Surgeon at The London
Clinic, has investigated the implications of MOM hip replacement
failure, and is one of the few experts in the UK who is able to
perform revision surgery on those affected.
For more information, please email info@thelondonclinic.co.uk
For press information, please contact The London Clinic Press
Office on 020 8786 3860 or email pressoffice@thelondonclinic.co.uk