Do Metal Ions or Debris from a Metal on Metal Hip Resurfacing Device Cause Health Problems?
Metal-metal bearings have advantages for active patients because their wear resistance is much greater than that of polyethylene, they do not fracture and they perform better with larger diameter balls. It has been known for three decades that the serum and urine levels of cobalt and chromium (the main elements in a metal-metal hip bearing) are increased in patients with a metal-metal bearing. The health impact of such ion levels has not been established and continues to be debated. Trace element analysis requires very sensitive equipment since the levels are in parts per billion (ppb). Absent some environmental exposure, serum and urine levels of cobalt and chromium are effectively zero in people with no metallic implants. In patients with a well-functioning total joint with a metal-on- polyethylene bearing, the serum levels are generally less than 1 ppb. In patients with a well-functioning prosthesis with a metal-metal bearing, the ion levels are generally between 1 and 5 ppb. These levels are very low and are 1/10th to 100 times less than posted industrial toxic levels. If there is any increase in overall health risk to patients with a metal-metal bearing prosthesis, it is very low. The JRI continues to closely monitor patients with metal-metal bearing prostheses to better define the benefits and risks of this technology.
There is one potential problem with metal-on-metal bearings. Normal wear results in release of metal particles into the body. One problem with any artificial bearing surface is the wear regenerated by normal daily wear and tear. Large volumes of plastic generated by metal on plastic (traditional) replacements result in large amounts of bone destruction, (osteolysis) around implants and has been the major cause for failure in young patients. Both ceramic-on-ceramic and metal-on-metal devices generate about 99% less wear debris than traditional bearings and the debris generated seems to cause less irritation to the bone than plastic debris does. There has been some speculation of the potential for metal debris to cause cancer. However, with careful studies to date, no links have been demonstrated.
My opinion is that the advantage of metal on metal bearings strongly outweighs the potential risks. Now we can return patients to normal function with almost no restrictions and expect their implants to last more than 10 years at very high activity levels. Most patients will never require another operation on their hip. If ceramic-on-ceramic or metal-on-crosslinked polyethylene bearings are used, wear is also not a problem, but significant restrictions remain. No running or jumping can be allowed due to the risk of fracture of the implant: no crossing of the legs or extreme bending can be allowed due to the risk of dislocation. I am surprised that any person would choose anything other than a large metal-on-metal bearing!
Metal ion dispersal
The current generation of surface replacements are metal-on-metal bearings. That means both the ball and the socket are made entirely of metal. Although this cuts down dramatically on the wear and tear of the components, it has been shown to cause metal ions to be dispersed through the body. Cobalt and chromium ions are measurable in the blood stream, but have not been shown to cause cancer or any other disease in humans. Although the metal ions are measurable, no one knows what a safe level is. Generally, people with functioning kidneys are able to excrete the ions in their urine.
The level of metal ions depends most on the position of the implants. It they are put in right, the level is low. The ion levels are no higher for a well-positioned resurfacing than they are for a MoM total hip.
1st February 2012
Metal-on-Metal Implants – Addressing the Negative Press
More information can be found here:
We have been receiving phone calls following recent press reports on failed metal-on-metal hip implants. We understand these sensationalist stories may cause anxiety among some patients. However, we would like to reassure our patients that these reports mostly concern failures with the DePuy ASR and the DePuy ASR XL, not the Birmingham Hip Resurfacing (BHR).
Many press reports imply these failures relate to all metal-on-metal hip resurfacings. A patient featured in a recent Daily Mail article, like many others, had a failed ASR. A critical point, omitted from the print version of the Daily Mail, can be found in the full on line version. As well as her ASR, the patient had a BHR on her other hip. She comments, "I’ve never had a minute’s trouble from the Birmingham hip – if only I’d had it on both sides."
High failure rates with the ASR and ASR XL have been widely documented. Both devices have now been withdrawn from the market. Research indicates the side effects, such as muscle damage, are specific to the ASR and do not apply to the BHR which is a very different device.
Earlier this week, the MHRA (Medicines and Healthcare products Regulatory Agency) issued another statement about metal-on-metal hips, in which they say, "On the evidence currently available the majority of patients implanted with metal-on-metal hip replacements are at low risk of developing any serious problems.”
In addition to the MHRA’s guidance, we wish to emphasize that Mr McMinn’s results with the BHR show a 97% survival in men and women of all ages at 14.5 years. Furthermore, excellent results with the BHR have been documented in National Joint Registers from around the world.
Sadly, these ASR failures come as no surprise. Mr McMinn has been warning about the device since it went to market in 2003. You can see Mr McMinn’s argument against the ASR here
Furthermore, The McMinn Centre has put together several resources which address patients’ concerns and the differences between the ASR and BHR designs. These resources are as follows:
• The McMinn Research Team’s detailed response to list of questions on metal-metal implants & metal ions provided by hip resurfacing users here
• The McMinn Centre’s response to a Channel 4 documentary on metal-metal hip replacements here
• An interview with a patient who has now had his McMinn metal-metal hip resurfacing for 20 years here
If you do have any concerns, please call:
The McMinn Centre on 0121 455 0411