Next-gen metal-on-metal hip implants: Test from every angle or face the consequences
Metal-on-metal hip implant problems are not a recent issue. In the 1970s, studies of early versions of the devices showed serious adverse reactions from cobalt and chromium ions released over time as part of standard wear-and-tear.
Studies indicated that cobalt-chromium implants would release metal ions that could infiltrate local tissue with long-term adverse effects, including, in some cases, permanent disabilities.
But their potential promise – a lifetime of reliability, resistance to wear-and-tear, a lower risk of dislocation and a more active lifestyle – were hard to resist.
So, despite early indications of metal-on-metal’s health risks, hip resurfacing with metal components saw a resurgence in the late ‘90s and 2000s. The hope was that innovation would reduce the risks seen in earlier versions.
Over time, however, similar problems emerged for all makers of MoM hips. Johnson & Johnson’s woes are but one example: In 2010, its DePuy subsidiary recalled the ASR hip prosthesis; in 2012, J&J pulled the Pinnacle implant; and last year the company agreed to settle a raft of product liability claims for $1 billion. (MoM hip makers still face thousands of similar lawsuits.)
Metal-on-metal implants are a good case study of a major hurdle device makers face: How to appropriately test implanted medical devices meant to last a lifetime.
“It’s a tough one, because it’s an implant. It’s hard to say, ‘Let’s do a bunch of studies and watch a bunch of users with this implant.’ I mean, you do say that, but you can’t,” KraMer said.
“You’d have to backpedal and say, ‘Where along the way could they have done something different that could have alleviated this decision to go metal-on-metal?’ That’s a hypothetical guessing game at this point, but they certainly couldn’t have found out that repetitive, usage-bearing weight is going to do this unless they set up some sort of long-term tests,” he explained.
With external devices, user testing can provide input on material use. But with an implant, patient feedback doesn’t cover the material; as KraMer observed, only long-term studies would have detected the long-term effects of micro-sized particles.
But he theorized that attempting to think outside the paradigm of medical device development could have caught the problem.
“It’s a tough scenario. Maybe you could look at the automotive industry and say, ‘Well, you know, pistons and cylinders in a car’s engine undergo a lot of revolutions. What do they do to not have particulate?’” KraMer said. “Maybe you could learn some lessons there. You could talk to mechanics and automotive engineers and find out when does this go bad, and what causes it to go bad. What causes it to go wrong? And then try to use those ideas to create your own tests for your specific implant.”
For now, metal-on-metal hip implants are mostly disused again due to the array of problems that cropped up with them, and testing may never get done to explore how to improve the devices to avoid shedding dangerous metal particulate.