Metallosis is a reaction in the tissues around a hip implant to tiny particles of metal wearing off it. Strictly, the word describes the dark grey staining these particles leave in the tissue. Doctors usually group it with related problems under the name adverse reaction to metal debris (ARMD). These include inflammation around the joint (sometimes called ALVAL) and, in some people, a fluid-filled or solid lump called a pseudotumour. Despite the name, a pseudotumour is not a cancer.
When two metal surfaces rub against each other inside the hip, tiny amounts of cobalt and chromium wear off. The same can happen where metal parts of an implant join together and slowly corrode. Some of this metal stays in the tissue around the joint; some gets into your blood. Most people's bodies cope with it. In some, the tissue around the hip becomes inflamed. In a very small number, blood levels climb high enough to affect other parts of the body. Metallosis is seen mainly with metal-on-metal hip replacements and resurfacings, and much less often with other types of hip.
Probably not. Most people with a well-functioning metal-on-metal hip never have a problem. Regular check-ups in the UK are there to find the few who do, early, while the tissue is still healthy and any further surgery is simpler. If you have a metal-on-metal hip and something feels different, look at the symptom list below to see whether you need to be seen soon, and make sure your yearly check-up is up to date.
All artificial joints shed some particles as they wear. With a metal-on-metal hip these are cobalt and chromium. They are small enough to be picked up by cells, carried around the body and into the bloodstream. At low levels this does no harm. At higher levels, problems can show up in two ways.
The first is around the hip itself. The soft tissues can become inflamed, fill with fluid or develop a pseudotumour. This especially affects the joint lining and the muscles on the side of the hip that you use to walk (the abductors). How much metal wears off depends on the size of the bearing, how well the parts are positioned, the implant design and how active you are. Smaller bearings, and cups set at the wrong angle, tend to wear more.
Rarely, the effects reach beyond the hip. If cobalt in the blood stays very high for a long time, it can affect the heart, the thyroid and the nerves, and occasionally eyesight or hearing. This nearly always happens with an implant that is failing badly, but it is why blood tests are central to monitoring in the UK.
Most cases are found at routine check-ups, before any symptoms appear. When symptoms do come on, they fall into two groups: those that need to be seen soon, and those that can wait for your next yearly review.
If anything on the "get seen soon" list applies to you, contact the hospital where your hip was done, or book a private review. If you've had both hips done, say which side the symptoms are on when you call. Yearly check-ups pick up slow changes; the list above is there for the quicker ones.
There isn't a single test. The diagnosis is built up step by step, and most people only need the first few steps.
Your surgeon will ask about your symptoms, see how well the hip moves, test the muscles at the side of the hip and watch you walk. You may fill in a short questionnaire, such as the Oxford Hip Score, so your answers can be compared with earlier visits.
Two X-rays, one of the whole pelvis from the front and one of the hip from the side, show whether the implant is still in the right position and whether it has loosened or bone has been lost around it. Most people have these at their yearly review.
The sample is taken through a small plastic tube rather than straight from a metal needle, so the needle itself can't affect the result. The UK medicines regulator, the MHRA, uses 7 µg/L (micrograms per litre) as its action level for either metal. Above that, the test is repeated after three months and a scan is arranged. The trend matters as much as any single result: levels that keep rising over several tests are a reason to look sooner, even if each one is under 7.
Ordinary MRI pictures are blurred by the metal in an implant. A special type called MARS-MRI (metal artefact reduction sequence) reduces that blurring and is the main scan used to look at the soft tissues around a metal-on-metal hip. An ultrasound scan by a specialist radiologist is a good alternative. Either scan looks for fluid, pseudotumours and damage to the muscles around the hip.
If infection needs to be ruled out, a needle is passed into the hip under local anaesthetic, guided by ultrasound or X-ray, and a small sample of fluid is drawn off. The lab checks it for signs of infection and tries to grow any bacteria, which can take a week or two. The procedure takes about half an hour, and most people are a little sore for a day or two. With metallosis the fluid is often dark grey or bloodstained, which is a useful clue in itself.
Surgeons can usually recognise metallosis as soon as they open the hip. The tissue around the joint is stained grey-black, the nearby muscles look dull and fragile, and any fluid tends to be dark grey or brown, sometimes compared to engine oil. Under the microscope the tissue shows damage and inflammation, with metal particles visible inside the cells that normally clear debris away.
Everyone in the UK with a metal-on-metal hip should have check-ups for life, following guidance the MHRA set out in 2017. The guidance sorts implants and patients by risk. Higher-risk implants are watched more closely, such as the DePuy ASR range and large-head metal-on-metal hip replacements with a stem. So is anyone with symptoms. A separate 2025 alert covers one type of hip replacement stem (Profemur cobalt-chrome modular necks), and around 2,000 people in the UK with it are being invited for review.
In practice, check-ups usually look like this:
These check-ups aren't a treatment. They are there to spot changes early, while the tissues around the hip are healthy and anything that needs doing is simpler.
Treatment follows three steps. Which one applies to you depends on your symptoms, how your blood results change over time, what the scans show and which implant you have.
Monitor
No symptoms, blood levels under 7 µg/L and no change on scans. Yearly check-ups carry on.
Scan
Symptoms, blood levels of 7 µg/L or more, levels that keep rising even below 7, or an implant that looks out of position on X-ray. You'll have an MRI or ultrasound scan and see a surgeon experienced in revision surgery.
Revise
Symptoms getting worse, a pseudotumour that grows between scans, blood levels that stay high with a higher-risk implant, muscle damage on MRI, or any solid pseudotumour. An operation to replace the implant (a revision) is planned.
Surgeons now tend to recommend revision earlier than they did ten years ago. Results are better when the operation is done before the tissue and bone around the hip are badly damaged.
Revision for metallosis is a bigger operation than a first hip replacement. The metal implant is taken out, along with any pseudotumour and damaged tissue. The hip is then rebuilt with a bearing that doesn't put metal against metal, usually a ceramic ball in a hard-wearing plastic socket. If the muscles are badly damaged, a socket designed to lower the risk of dislocation (a dual-mobility cup) may be used. If bone has been lost, extra pieces or custom-made parts may be needed. Recovery usually takes longer than after a first hip replacement, with a longer hospital stay and more time to get back to normal.
Results are good for most people. The largest UK study looked at more than 2,500 revisions for metal reactions recorded in the National Joint Registry. About 9 in 10 of those revised hips had not needed a further operation five years later.
The full revision pathway, from scans and anaesthetic to the operation and rehab, is explained on Mr Hussain's main practice site.
Revision hip replacement (main site)Mr Hussain also performs revision surgery; read more about his work as a revision hip surgeon in Birmingham.
Metallosis is mainly a problem of metal-on-metal hips. Ceramic-on-ceramic resurfacings, such as the ReCerf and the H1, don't release cobalt or chromium where the surfaces rub together, so they can't cause metallosis in the same way. For anyone choosing a resurfacing today, the risk of metallosis mostly comes down to which bearing is chosen, and why.
Mr Hussain does still use one metal-on-metal implant, the Adept, but only for a specific group: active men with larger hip joints (48 to 58 mm). That is where metal-on-metal has its longest and strongest track record, with an ODEP 15A rating, meaning at least 15 years of strong outcome data. The problems described on this page were concentrated in smaller bearings, smaller hips, cups set at the wrong angle and surgeons who did fewer operations, and choosing patients carefully is designed to avoid all of them. Women, anyone who may have children in future, people with smaller hips, kidney problems or a known metal allergy, and anyone who would rather avoid lifelong blood tests are offered a ceramic implant instead. Everyone with an Adept has the lifelong blood tests and check-ups described above, so that a problem, if one ever starts, is found early.
Reactions to metal debris aren't only a problem of older metal-on-metal hips, though. A small number of cases have been reported with ceramic and dual-mobility hips, caused by corrosion where metal parts join. That isn't a reason to avoid modern implants. It is a reason to take any new hip symptom seriously and keep up with follow-up, whatever type of hip you have.
For more on hip resurfacing today, including ceramic bearings, see Hip Resurfacing, or read how metallosis compares with the operation's other risks in the guide to hip resurfacing complications.
If you have a metal-on-metal hip and would like a private review, or a second opinion on your test results, you can book a consultation at any of Mr Hussain's three Birmingham hospitals. Please bring your latest scans and any previous blood test results.
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