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What you need to know about knee replacements

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Replacement knee joints are giving thousands of Kiwis decades of service, but don’t rush to get one.

A year after Kevin Powell had his right knee replaced, he’s enjoying being able to get out of a chair, push his lawnmower and walk up and down stairs without pain. The Christchurch account manager reckons he could easily walk 10km, and he knows he can bike 100km without problems because he’s done it.

Like most people who have either a total or partial knee replacement, Powell was in his mid-sixties when he had the surgery, which was done in March last year using private health insurance. And like 95% of his fellow patients, he had his knee replaced after experiencing increasing pain and disability caused by osteoarthritis.

For Powell, the mild discomfort that forced him to give up playing soccer and take up cycling gradually worsened. “It deteriorated a lot between the ages of 60 and 66. It was a real nuisance and it prevented me from doing a number of things. It even got to the stage where it was difficult to cycle.”

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He says the relatively long post-surgery recovery period – he took four weeks off work, then spent several more weeks working part-time – has been worth it. That’s particularly so as it’s unlikely he’ll ever have to do it again.

It used to be thought that a knee replacement would last 10 to 15 years. However, a study published in the Lancet in February found that 82% of total knee replacements last 25 years and 90% last 20 years. Partial knee replacements, which are performed less often, have a slightly poorer longevity, with 70% lasting 25 years. In comparison, only 60% of hip replacements last 25 years.

Andrew Vincent, president of the New Zealand Orthopaedic Association’s knee and sports surgery society, says the association’s joint register tells a similar story, with only 6% of patients having revision knee surgery since the register began in 1999.

He says even if you live into your eighties and beyond, you’re likely to be much less physically active, which means your new knee should keep working. “Basically, if you’re over 60, there’s a 90% chance it will be the last operation you will have on your knee.”

Andrew Vincent. Photo/Supplied

The first knee replacement was performed in 1968. Since then, the operation has become increasingly common. Joint registry figures show that between 1999 and 2007, fewer than 4000 New Zealanders had a total knee replacement, in which metal and plastic parts are used to cap the ends of the bones that form the knee joint, along with the kneecap. In 2017, 8298 people had the surgery, with another 1054 having a partial knee replacement, in which only a portion of the knee is resurfaced.

Demand is expected to increase as the population ages, with US data suggesting demand may almost double by 2026. In New Zealand, this is putting increasing pressure on the public health system. At present, district health boards use a scoring system to determine who qualifies for knee-replacement surgery. Access varies between DHBs, and there are concerns it will become even more limited as demand increases.

For those lucky enough to qualify – or who, like Powell, have private health insurance – most find the surgery life-changing. However, Vincent says international figures suggest up to 15% of people are not satisfied with the result. They continue to feel pain, or they complain that their new knee doesn’t function as well as they had expected.

He says it’s important to understand that a replacement knee is not the same as a real knee, and it won’t function as well, either. You won’t be able to go running after surgery or play sports such as soccer or netball.

“A good functioning knee replacement will allow you to walk an unlimited distance comfortably, to cycle, to play golf, to go hiking, to probably play some careful doubles tennis and to ski on a bluebird day – but not 30 days a year.”

Although he now works mostly in the private health system, he encourages his patients to wait as long as possible before having surgery, on the grounds that they’re likely to be happier with the results. “I’m in favour of people being more symptomatic and having greater disability so they have more to gain.”

This article was first published in the May 4, 2019 issue of the New Zealand Listener.