Why hip and knee replacements last longer than ever now

We all know what it’s like to go and see the doctor to talk about your health. It can often be a lot to take in, especially when surgery becomes part of the conversation. At such a stressful time, patients can be forgiven for sometimes leaving a consultation with incorrect ideas about an operation. This can certainly be the case with hip and knee replacements—especially when it comes to how long someone can expect their new joint to last.  

These days, hip and knee replacements are commonplace. Around 200,000 of these procedures were carried out in England and Wales in 2022 alone. Given such popularity, it’s easy to forget that this is a relatively new form of surgery. Hip replacement has only been around since the 1960s and, over the subsequent decades, it has improved to the point of being praised as the "operation of the century” in The Lancet Medical Journal. 

The earliest hip replacements had their shortcomings. The joint’s stainless-steel ball would damage the plastic socket over time, causing a reaction that would lead to the bone being worn away, something surgeons refer to as loosening. Today, we tend to use a much more durable plastic, while newer ceramic balls have a far smoother contact with the socket.  

The same is true of knee replacements, with implants subtly evolving over the years to become more forgiving, conforming better to the shape of the original joint, ensuring a more comfortable experience for the patient. Meanwhile, the methods for attaching replacement joints have also improved, whether it's the “glue” used for cement fittings or the surface coatings on press-fit implants. 

We’re now at the point where there’s probably limited room for further improvements to joint implants themselves, although the introduction of 3D printing has seen some marginal advancements in the manufacture of replacement knees and hips when a specially fitted joint is needed (which is not the case for the vast majority of patients).  

Since being established 20 years ago, the National Joint Registry (NJR) has played a crucial role in the journey to improved reliability. During this time, the registry has collected data from more than 3.7 million procedures. From this data, we can see that there has been a 50 per cent reduction in the need for patients to have their joint replacement operated on again.

This is important, as when a joint replacement is redone, it doesn’t tend to last as long—the first one is usually the best. Nowadays, surgeons, armed with valuable NJR data, are more inclined to choose implants that offer superior performance, ultimately leading to improved outcomes for patients.

Twenty years ago, eight out of ten joints were expected to last two decades, but today, we anticipate that at least nine out of ten will achieve this impressive milestone.

When hearing this figure, a patient might get the impression that their new knee or hip will have a maximum lifespan of two decades, but this is not the case. In fact, it's now common for patients to have their replacement joints for 20 or 30 years without any issues.

There are a number of reasons why one in ten joint replacements fail to make it to the 20-year mark; thankfully, these are all relatively uncommon. These include infection, which occurs in approximately one in 200 cases.

Sometimes a joint replacement will need to be done again if there’s a break in the bone around it. In other cases, there can be persistent pain, instability, or other issues, but these remain infrequent. There’s also some evidence that severe obesity can also affect the risk of the replacement joint failing. 

When I’m asked by patients how long their joint replacement is likely to last, I tell them: “If you buy a new car, look after it, keep it in the garage at night, and drive sensibly, it'll last you for a very long time. However, if you treat it like a race car and thrash it around regularly, you're going to run into issues sooner rather than later.”

The fatalistic might find it reassuring to know that for the over 60s, who make up the majority of people requiring joint replacements, there’s a much greater chance that your new hip or knee will outlast you than that you will outlast it.

If you’re having this operation in your 30s, there's a pretty good chance that you will outlast your implant and it will need redoing in the future. We find that younger patients are often more active and put greater stress on their replacement knees and hips, and while the materials are very good, after a long enough time the bearing parts can become worn out. Despite this risk, if you're 30 and you've got bad arthritis, there's absolutely no benefit in waiting till you're 70 to get it replaced, as this would mean spending 40 years in unnecessary pain.

Joint replacement surgery is a relatively recent development in the grand scheme of medical science, and with ongoing innovation, we can hope for even greater longevity and success for these life-changing procedures. Indeed, with the NJR celebrating its 20th birthday this year, it's exciting to imagine what the data will reveal on its 50th anniversary.