We’ve known for a while that “minimally invasive” metal-on-metal hip implants are a gamble! They raise the levels of metal in the blood and cause local genetic instability in the cells, and we see adverse reactions, implant revisions, and even pseudotumors in patients who have had metal-on-metal hip implants. About the only thing you can bet on is that they will be a major player in serious hip replacement complications. So why are surgeons still rolling the dice on the use of metal-on-metal hip implants?
Due to the invasiveness of hip replacements for moderate to severe hip arthritis, “minimally invasive” hip replacements have become more common. This newer procedure (though “minimally invasive” is misleading as this generally refers to needle- or catheter-based procedures that don’t involve surgery) involves smaller incisions and the placement of a smaller prosthesis with a metal-on-metal hip implant design. This simply means that both sides of the prosthesis are made of metal which allows the smaller hip replacement components to survive the same forces. A serious problem with this design is that it sheds dangerous metal wear particles into the joint area and bloodstream. Now, another study confirms not just an increase in metal ions in the blood, but an ongoing increase in metal ions in the blood, supporting, once again, that these particular hip replacement complications are very concerning. Despite this and many other studies referenced on this blog in recent years (e.g., study 1, study 2, study 3), a quick search on the Internet shows that there are still many surgeons offering metal-on-metal hip implants.
The purpose of this new study was to complete a five-year follow-up on a prior study comparing metal ion levels in the blood of patients who had received metal-on-metal hip implants with a large-diameter femoral head. The study looked at 144 patients and four different types of implants . The ion levels measured over the five-year period included cobalt, titanium, and chromium. The study abstract states, “We found that ion generation and related complications varied among designs. More concerning was that, for some designs, ion levels continued to increase,” particularly with cobalt. So for some types of hips, the dangerous metal ion levels continued to climb. This study therefore calls into question other studies that showed a certain level of ion levels in the blood at a specific time point. Other findings included the following: adverse reactions due to the metals in the tissues around the implant, revisions of the implant, and, in one patient, a pseudotumor was being followed.
Debris from metal-on-metal implants has been shown to cause inflammation and lead to other adverse reactions, such as genetic defects and metal toxicity. Let’s explore some of the more common reactions.
One research study ties higher levels of metal in the blood to patients whose pain gets worse after a metal-on-metal hip replacement. One of the purposes of this “cross sectional cohort study” was to evaluate the relationship between elevated metal ion levels and the incidence of pain and functional outcome and quality of life after surgery. A staggering one in five patients required a revision surgery because of pain or other issues! Fifty-seven pseudotumors were found, which can also cause significant pain. Thirty-five percent of patients reported pain and also showed significantly higher cobalt and chromium blood levels compared to patients without pain. Patients with the lowest cobalt levels reported significantly less pain and significantly better outcomes on functional measures.
Hip replacements are supposed to be done to reduce pain and increase function, but with the correlation between higher blood levels of metal ions in the blood and more pain and poorer outcome, the odds are good that this is no coincidence.
Your chromosomes contain the instructions for your cells. They can be damaged by wear debris from hip replacement metals, and if that happens, your cells receive bad instructions for how to make the chemicals that keep you alive, leading to genetic problems. In addition, chromosome abnormalities could theoretically lead to cancer. While joint replacement wear debris causing inflammation and elevating serum metal levels is bad enough, having that debris mess with your chromosomes is a huge problem. What’s fascinating is that this could be why one large European joint replacement registry found an association between cancer rates and joint replacement.
This study used cells taken from patients who have undergone total hip replacements that were then grown in culture. It found that titanium wear articles from metal and polyethylene prostheses (a very common type of hip and knee replacement device) created chromosomal instability, reproductive failure, and gene damage in the cells for many generations. The damage was similar to what one would expect from cadmium poisoning or radiation exposure!
Hip replacement cobalt toxicity, or elevated cobalt levels, from metal-on-metal hip implants are a serious problem, but many doctors miss the signs and symptoms of cobalt poisoning. These include the following:
Another study shows higher cobalt and chromium metal levels in patients who had hip resurfacing when compared to traditional hip replacement. What was a shocker was that these patients have structural changes in their brains on MRI that weren’t found in the traditional hip replacement patients! Which areas had problems? The occipital cortex (where signals from the eyes are processed) is one of the regions of the brain that showed issues. The optic chiasm (the part of the brain where the eye nerves cross) also looked different in these patients. In summary, the structural changes in these patients seemed to revolve around the visual system. Problems with hip replacements and vision have been reported by others as well. Animal studies have shown that high cobalt metal levels can affect the nerves in the eye. Hearing and vision loss are also commonly associated symptoms with both chromium and cobalt toxicity.
A hip replacement revision is when the surgeon has to repair or remove an implant. This usually is done when complications result from the hip replacement surgery. These could include infections, pain, injury, even adverse reactions to the toxic metals in the blood.
In this study, the outcomes from metal-on-metal hip implants aren’t great. For example, for male patients with smaller femoral heads or female patients, hip resurfacing isn’t as effective as hip replacement. In addition, for women, many more of these implants were failing at five years sooner than traditional hip replacement devices. One of the rationales for hip resurfacing was that it might be better for younger and more active patients, since in patients under 55, only 72% of traditional hip implants last 10 years. However, this study shows that five-year revision rates for hip resurfacing were almost double that for traditional devices! So much for a better solution for younger people!
Revisions of metal-on-metal hip implants can be effective for reducing metal ions in the blood, though some metals can remain in the blood even after the implant is removed. Think about this for a moment, in some cases after the offending metal is removed, there’s still a problem!
As mentioned earlier, the obvious consequence of when metal rubs against metal is metal shavings, which then fill the joint area and cause high metal ions in the blood serum as well as black soot-like metal particles. The latter can cause strange tissue reactions, sometimes creating what looks like a tumor (pseudotumor). Pseudotumors can become very big—golf ball sized or larger—and press on the nerves, arteries, and veins near the hip joint, causing pain and other problems.
What are the odds of getting one of these pseudotumors? One study shows one-third of minimally invasive hip replacement patients get these tumors, so I wouldn’t recommend rolling the dice on this one.
The upshot? If you’re considering a “minimally invasive” metal-on-metal hip implant, step away from the Craps table; there are just too many studies showing this surgery is a bad gamble. You might want to learn more about how stem cells stack up against hip replacements.
Can a stem cell procedure help me? To find out if you might be a candidate for a Regenexx stem cell procedure, complete our Regenexx Procedure Candidate Form online.
About the Author
Christopher J. Centeno, M.D. is an international expert and specialist in regenerative medicine and the clinical use of mesenchymal stem cells in orthopedics. He is board certified in physical medicine as well as rehabilitation and in pain management through The American Board of Physical Medicine and Rehabilitation.…