Surgeon Showing Knee Implant X-Ray to Female Patient

A new polymer knee implant may offer new options for future knee replacement patients, but there’s a long way to go between now and then, as YKC’s Dave Duffy explains.

You may have seen some articles in the press recently about a new type of knee implant. Unlike most implants, which are primarily made of metal with some plastic and ceramic components, the new implant is an all-polymer device. According to the manufacturers, this new implant – which is undergoing pre-clinical trials at the University of Leeds – neatly sidesteps the issue noted by the Independent that 10% – 15% of people “are sensitive to the metals” used in implants. We’ll revisit that particular stat in a minute.


The case for polymer

It would be foolish to suggest that, just because we have an implant that works well for the vast majority of patients, there’s no point in trying to improve on it. It’s right to ask questions of the way we do things now. It’s also right to explore alternatives providing those alternatives are backed by reliable research. Certainly, the research into this polymer implant looks well-funded and of good quality.

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The challenge for polymer to overcome

The issue polymer (or any other new implant material) faces is building the body of evidence to support it. It’s a little like looking at a star in the night sky. Our view of even the closest star is a false one, because it has taken years for the light to reach us. We see it as it was, not as it is.

Similarly, we won’t actually know whether this polymer implant stands the test of time until that time has passed. That’s not an issue with metal implants because that time has already elapsed. We know current implants will last upwards of 20 years in many cases, because we’ve monitored patients and their implants for that long.

We don’t (and won’t) have the same data to support the polymer implant for years yet. That doesn’t mean it isn’t worth developing new forms of implant using new materials, but there’s no escaping the fact that it will be many years until we can say with certainty that they are as good as or better than existing technology.


Metal hypersensitivity

One area in which the implant’s manufacturers anticipate opportunity is in the 10% – 15% of patients often quoted as having hypersensitivity to metal. There is, however, a challenge to overcome here too, because although some studies have found a potential causal link between cobalt, nickel and similar metals and ongoing joint pain, others suggest the condition is not only rare but that there is no real evidence to support it.

There’s no question that more research into hypersensitivity is required. Until we have that, this research from 2018 which states that “a painful total joint is most likely painful due to a number of other reasons” is probably as close to the truth as we can currently get.


The role of the National Joint Registry

We can’t know whether the polymer implant will affect hypersensitivity because more research is needed into hypersensitivity. Nor can we know at this stage whether the implant will last 15-20 years because it hasn’t had 15-20 years. But we don’t want to stifle innovation.

What we can do, therefore, is monitor progress, and this is the role of the National Joint Registry (NJR). The NJR monitors the progress of all implants and picks up any aspects of performance that fall below expectations. As time passes, we’ll develop a greater understanding of whether metal implants remain the right option, or whether polymer will be the hip and knee implant material of the future.

To discuss your knee replacement, contact us or phone us on 03453 052 579.

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>  Discover more about partial or total knee replacements

Dave Duffy

Dave Duffy

Private appointments weekly at The Duchy Hospital Harrogate & Nuffield Hospital Leeds

Private Secretaries

Amanda Hardy
The Duchy Hospital Harrogate
07889 485 579

Lauren Long
Nuffield Leeds
07930 585 744

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