… and why are some knee implants cementless? Jim Newman explains.
When you have a knee replacement, what is it the holds the implant in place? It’s an important question. Without something to connect the implant to the bone, there’s a risk that putting all your load through the knee could, over time, cause the implant to fail or loosen. Since the very earliest days of knee replacement surgery, that issue has been resolved using a medical cement.
The cement (actually it’s more like a grout) ensures load is evenly distributed throughout the joint. It also contains an antibiotic that is released over time, reducing the risk of infection. The cement is a tried and tested method – which begs the question, why do some newer implants not use cement?
How do cementless implants work?
Cementless implants take a different approach to knee replacement. Zimmer Biomet, for example, uses a trademarked material called Trabecular Metal. Highly porous and made of tantalum, when you implant it, a special coating encourages the bone to grow into the metal’s pores, creating a biological fixation rather than a cemented one.
Cement vs cementless
Cement has numerous advantages, not least that it’s by far the cheaper option. Yet cementless implants may have some advantages over cemented. Cementless procedures are quicker. Although extremely rare, it is possible to have an allergic reaction to bone cement, something that clearly can’t pose an issue when you don’t use cement. Additionally, there is a feeling that biological fixations may be a better option for younger patients, although that hasn’t yet been borne out by any studies.
And this the problem cementless implants face. They may perform brilliantly, but if you want to understand with certainty how long an implant lasts, you have to implant it and wait. Today’s knee implants last up to 25 years. With many cementless implants having been developed in the last decade, we have a good while to wait yet before we can start to say with certainty that cementless is the better option.
But whilst insufficient time has elapsed to know for sure how long cementless implants last, we do have that information for cemented implants, and the information is good. Right now, it’s hard to see how we might justify a costly procedure that we suspect will work well ahead of a less costly procedure that we know works well.
That said, if a study in 15 years’ time were to say that cementless implants were effectively lasting forever and never loosened, I wouldn’t be surprised.
There is growing evidence for cementless. The theory is sound. We just don’t have concrete (pardon the pun) evidence. Yet. So for now at least, you can expect your knee replacement to be cemented in place.
Consultant Knee Surgeon at the Yorkshire Knee Clinic
“I couldn't recommend him highly enough.”
Charles Turner, YKC patient
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