Many newspapers and TV stations have reported that medical regulators have launched an investigation into a type of hip replacement called a metal-on-metal (MoM) device (DePuy ASR hip replacement implant).
The concern is that as the hip replacements wear down, metal particles can be released from the artificial hip, react with the soft tissue (such as muscle and ligaments) surrounding the joint and enter the bloodstream. In 2010, the UK regulator, the Medicines and Healthcare products Regulatory Agency (MHRA) issued a product recall for DePuy ASR, a brand of MoM artificial hip. This meant that surgeons were told not to implant DePuy ASR hip replacements and return any unused implants to the manufacturer.
The MHRA has urged surgeons to tell all patients that had received these DePuy ASR hip replacements about the recall, and to schedule them for annual follow-up visits. If the person who had a DePuy ASR hip replacement implant experiences pain, the surgeons should consider measuring the level of metals in their blood and should examine the soft tissue to see if reactions have occurred. If necessary, removal and replacement of the implant should be considered.
The Sunday Telegraph has brought this story to the public attention again because of what it says are subsequent developments. The Telegraph claims that the risk from the devices is greater than previously thought, with greater failure rates. The Telegraph says that the MHRA is drawing up a new alert for anyone with any type of metal-on-metal hip replacement. Channel 4 News reported that around 30,000 people in Britain have received MoM hip replacements.
A statement about the hip implants from the MHRA, issued on January 30 2012, said: “The majority of people with metal on metal hip replacements are at low risk of developing any serious problems. We are continuing to closely monitor all evidence. This needs more analysis before any conclusions can be drawn and further advice given. We have already taken prompt action to investigate safety concerns and have provided advice on patient management to relevant healthcare professionals.”.
Medical devices, like medicines, are regulated but are coming under more scrutiny, from both the regulators and the media following widespread concerns over the emergence of faults with illegally made PIP breast implants. Find out the latest NHS information on PIP breast implants.
What types of hip replacements are there?
In the UK, approximately 70,000 hip replacements are performed each year. In a total hip replacement operation an artificial ball is attached to the top of the leg bone and an artificial socket to the hip bone. The socket can be made out of plastic or ceramic, while the ball is metal. The ball is attached to a shaft, which is placed in the hollow of the leg bone (femur). Some people do not need a total hip replacement, but have a hip resurfacing operation. This has the advantage of removing less of the person’s own bone. The joint surfaces are replaced with metal inserts that cover the surfaces of the hip but do not extend down the inside or hollow of the leg bone. The metal mixtures used in hip replacements contain the metals chromium and cobalt.
What are the risks of problems following a metal-on-metal hip replacement?
When hip resurfacing was initially introduced, metal-on-metal (MoM) replacements were popular, especially with younger, active patients. An article by two orthopaedic surgeons working in Britain and published in the British Medical Journal in 2011 said that they were used in 10% of hip operations between 2006 and 2009, and 50% of all hip replacements in people younger than 50 years. However, problems with the metal resurfacing included raised chromium and cobalt in the blood, loosening of the joint, hip fracture and soft tissue reactions around the hip. It reported that problems with metal on metal hip replacements could include reactions to metal debris and associated pain, swelling, loss of movement and limping.
In March 2011, delegates at the British Hip Society annual conference discussed MoM hip replacements. Units in Belfast, Southampton, Cardiff and Stockton-on-Tees that had researched the outcomes for people who had these devices fitted over the short- to mid-term, said that a high proportion of MoM devices from other manufacturers may also be showing similar results to the withdrawn DePuy device. They found that, overall, the MoM devices showed a higher than anticipated early failure rate (most hip replacements last about 20-30 years). They found that 49% of people who had been fitted with the DePuy device needed to have it replaced by six years and between 12 and 15% who had other metal-on-metal hip replacements needed these to be replaced by five years. They said that the patients whose replacements failed tended to come to the doctors when they experienced pain. X-rays showed some patients had loosening of the joint, and some patients had raised levels of cobalt and chromium in their blood.
The inclusion of the word “poisoned” in some newspapers is likely to be wrong. Metal from the hip replacements can enter the bloodstream, but the levels of cobalt and chromium found give an indication of the wear to the hip replacement. No evidence for damage other than local tissue damage was presented. The MHRA’s advice is to monitor the level of chromium and cobalt to see if a patient requires further follow-up.
What is the advice for people who have had a MoM hip replacement?
The MHRA has not issued new guidance as yet. However, the report from the British Hip Society annual conference says that they believe that the existing advice from the MHRA still applies. This means that people who have been treated with a MoM hip replacement should be followed up regularly for five years and probably for the life of the implant. People with the withdrawn MoM hip replacements who experience pain should have this thoroughly investigated. Following the withdrawal of the DePuy device, and the MHRA guidance, the British Hip Society and the British Orthopaedic Association said:
- Everyone with a hip replacement that has been withdrawn should be informed and told that they will be under close clinical follow-up.
- Some form of follow-up should be carried out at least annually and patients should be given contact information so that they can be reviewed quickly if they have pain or lose function in their hip.
- Patients should be followed for the life of the implant until more data are available. If someone with a withdrawn MoM hip replacement experiences no pain or loss of function, no further investigations are required apart from standard follow-up.
- If a person with a withdrawn MoM hip replacement reports that they are in pain, the cause of the pain should be further investigated. Blood cobalt and chromium levels should be measured to indicate how much the device has worn, but there is no evidence that the implant must be replaced above a certain metal concentration.
- Treatment decisions should be confirmed with a second experienced “revision” surgeon.
People who have had a hip replacement, who are concerned, should contact their orthopaedic surgeon or GP. They should be given records of the type of hip replacement they had and receive the follow-up, if any, that is required.
- MHRA: Joint Prosthesis - DePuy International Limited - A Johnson & Johnson Company - Recall; Metal-on-Metal; NJR; National Joint Registry; Resurfacing; DPYOUS2. March 2010 (updated August 2010)
- MHRA: Medical Device Alert: ASR™ hip replacement implants manufactured by DePuy International Ltd (MDA/2010/069). September 7 2010
- British Hip Society and British Orthopaedic Association: Large Diameter Metal on Metal Bearing Total Hip Replacements (PDF, 73kb). March 2011
- British Hip Society and British Orthopaedic Association: Withdrawal of DePuy ASR Resurfacing and XL metal on metal bearings – information for and advice to surgeons (PDF, 114kb). October 25 2010
- Skinner J, Kay P. Commentary: Metal on metal hips. British Medical Journal. Published online May 14 2011.