A study of metal-on-metal hip implants found that the metal ions released when the parts of the cobalt-chromium-molybdenum devices rub against each other were able to penetrate into bone marrow, where they impeded the formation of bone-growing cells.
Metal-on-metal hip implants came under intense scrutiny following the high-profile August 2010 recall of DePuy Orthopaedics’ ASR XL acetabular and ASR hip resurfacing systems. Johnson & Johnson pulled the devices off the market after receiving reports that a higher-than-normal number of patients required surgeries to correct or remove defective implants. The devices, many of which have been recalled or otherwise pulled from the market, have been found to deliver failure rates as high as 43% after 9 years.
Some reports warned that hundreds of thousands of patients may have also been exposed to toxic compounds from metal-on-metal implants, putting them at risk of developing cancer, cardiomyopathy, muscle and bone destruction and changes to their DNA. Since 2010 the controversy has ensnared other device makers, with personal injury lawsuits piling up even against metal-on-metal implants that haven’t undergone a recall.
The new study, published in the August issue of the journal Biomaterials, found that cobalt and chromium release contributes to bone loss. A Berlin-based team of researchers tested adjacent tissues, joint fluids and bone marrow to discover that both metal particles and dissolved metals play a role.
Dissolved metal ions in bone marrow interfere with mesenchymal stromal cells, the precursor to the osteoblasts that mineralize bone. Analysis of marrow with high metal concentrations showed that the MSCs had lost the ability to form osteoblasts; the team of physicians and researchers from Charité – Universitätsmedizin Berlin and DRK Klinikum Westend then duplicated the effect by exposing cell cultures to equivalent levels of chromium and cobalt.
“Considering the adverse effects of wear products from CoCrMo on MSCs, our data imply that the use of this alloy for mechanically loaded articulating surfaces and taper connections should be carefully reconsidered,” the study’s authors wrote.
“In order to ensure long-term success and an implant lifespan of more than 15 years, we need to further improve our understanding of the biological effects of the materials used, in particular those of the implanted metals,” Dr. Carsten Perka, Medical Director of the Center for Musculoskeletal Surgery, said in prepared remarks. “This is why we will further encourage and promote interdisciplinary collaborations between physicians, toxicologists and biologists at the Berlin-Brandenburg Center for Regenerative Therapies.”
In February, the FDA said it would require the manufacturers of metal-on-metal hip implants to put the devices through its stringent pre-market approval process. The federal safety watchdog said its final order affects 2 types of MoM hips: Hip joint metal/metal semi-constrained with a cemented acetabular component, and hip joint metal/metal semi-constrained with an uncemented acetabular component.