Patients who have had older types of hip replacement may be at greater risk of heart damage than previously thought, researchers have said, because of cobalt leaching out of so-called metal-on-metal implants.
Tens of thousands of UK patients were fitted with these devices during the 2000s, when they were marketed as a solution for young, active patients who needed a hip replacement that would last a lifetime.
The issue is that tiny metal ions made up of cobalt and chromium are thought to break off from the implants and leak into the blood, and there are fears this could cause muscle, bone and organ damage.
Surgeons began to voice concerns about the implants in 2008, and in 2012 the Medicines and Healthcare products Regulatory Agency (MHRA) issued guidance recommending annual blood or MRI checks for patients who had received them. Since then, mounting evidence has suggested that such individuals may be at greater risk of heart disease.
The new study, funded by Heart Research UK, set out to investigate this link in more detail and find ways of predicting which patients are at greatest risk.
Susan Currie, an associate professor in cardiovascular physiology at the University of Strathclyde, and her colleagues analysed blood samples from 30 people with metal-on-metal hip replacements and identified variable levels of cobalt in their blood. They then used a highly sensitive form of ultrasound called global longitudinal strain to assess the heart health of 16 of these patients, as well as eight healthy controls.
“This is a much more sensitive measure of heart contractility than an echocardiogram [ECG] but it is not something that’s routinely looked at,” Currie said. “All of the patients had normal echocardiogram function, but when we scratched the surface using a much more sensitive method, some of those patients had abnormal contractile function, and there’s no way that you would pick that up with a routine check.”
Further experiments in cultured heart cells suggested that cobalt interferes with calcium levels in heart cells, reducing their ability to contract, which could lead to heart dysfunction in some patients. The research will be presented at a meeting of the Northern Cardiovascular Research Group in Manchester this weekend.
Currie stressed that only a small proportion of patients fitted with this type of hip replacement were likely to be at risk. “We’re talking about a very small percentage of people who are going to develop heart disease – but in some cases it’s heart failure, so this is something that cannot be ignored,” she said.
Helen Wilson, the director of research at Heart Research UK, said: “This study has helped us to understand the link between hip replacements containing cobalt and the development of heart disease, something that we previously had limited insight into.
“The team has also made progress towards developing a test to measure the risk of heart damage. In the future, we hope this will improve outcomes for hip replacement patients by reducing the risk of them developing heart failure which can be a debilitating and serious condition.”