Metal-on-metal (MoM) hip replacement implants generally last well and don’t cause problems. However, some people are experiencing complications possibly related to the metals used in the implants – usually chromium and cobalt. It’s important to be aware of symptoms that may indicate complications with these implants and visit your orthopaedic surgeon or GP if certain symptoms appear.
Hip replacements can help people with hip arthritis or injury to have less pain and better mobility. Around 34,000 hip replacements were performed in Australia in 2010.
Hip replacement implants can be made from a number of materials, including metal, ceramic, ceramicised metal or polyethylene.
Hip replacement implants are either used to totally replace the hip joint, or to protect the existing hip joint in a process known as hip resurfacing. Hip resurfacing involves trimming away the damaged bone and cartilage of the hip joint then capping the joint bones with metal to prevent further damage.
Metal-on-metal (MoM) hip replacements, where the ball (head) and socket component are made from metal, have been available since the 1960s but there has been an increased use of these implants in the last 10 years. Being made totally of metal, MoM implants are more durable than other hip replacement systems. Because of this, they are often given to younger and more physically active people.
Most MoM hip replacements work well and don’t cause problems. However, problems can arise when tiny particles of metal are shed into the joint area due to general wear and tear of the metal joint over time. This debris can result in the release of metal ions into nearby tissue, which may lead to local damage and inflammation, increasing need for a second procedure to replace the first hip implant.
Symptoms that may indicate metal implant problems include hip, groin or leg pain, swelling around the hip region, numbness, or a reduced ability to walk.
If you experience pain, swelling, numbness or problems walking 3 months or more after a hip replacement operation you should see your orthopaedic surgeon. Your doctor will assess you and suggest tests to determine the cause of your symptoms and to see whether these symptoms may be due to your hip implant or another problem.
Chromium and cobalt metal ions occur naturally in the body. People with MoM implants have higher levels of these metal ions than those without, but it is not yet clear if these raised blood levels are high enough to cause health problems.
In rare cases the release of metal particles and ions into the blood stream may lead to metal poisoning over time. This can affect other parts of the body such as the heart, nervous system, kidneys and thyroid gland.
It isn’t possible to predict who will experience metal poisoning as people react differently. If you experience any new symptoms after your hip operation in areas away from your hip, see your GP and be sure to remind them about the implant.
The effectiveness and safety of the joint replacement systems used in Australia is monitored by the National Joint Replacement Registry, which collects and assesses information on joint replacement operations throughout Australia.
Evidence from this and similar registries from other countries has led to the withdrawal of certain MoM joint devices, usually due to a higher than expected rate of patients with these particular implants needing to re-do hip surgery.
Hip operations that use MoM joint implants make up a small percentage of all hip replacement operations performed in Australia. If you are concerned whether your implant puts you at risk, talk to your doctor.
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Last published: 31 July 2012
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