‘How long will my artificial knee last?’

In the region of 10,000 hip and knee replacements are carried out in Ireland every year. Recovery times post surgery have reduced dramatically, with hospital discharge after three to five days now the norm.

For those offered elective joint replacement a big question is: how long will my new joint last? Leaving aside postoperative complications, such as bleeding, infection or dislocation, nearly every patient offered a new hip or knee wants to know the likely life-span of a new joint.

The main reason why you might need a new knee joint is osteoarthritis, a “wear and tear” form of joint disease. Knee replacement is the mainstay of treatment for end-stage osteoarthritis.

You will notice I didn’t list old age as a cause for osteoarthritis of the knee. I learned not to do this some years ago when an older gentleman asked my opinion as to why he had developed arthritis in his right knee. “It’s because of your age,” I replied. Fixing me with a look of disdain, he said: “If that’s the case, why is my left knee not causing any trouble? It’s the same age as my right one.”

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Relief of pain

The aim of knee replacement surgery is the long-term relief of pain and restoration of function. However, knee replacements may fail for a variety of reasons, including loosening, infection, persistent pain and instability, and so might require revision. But revision is expensive and the outcome is worse than first-time knee replacement.

The recently established Irish National Orthopaedic Register will record all hip and knee replacements performed in Ireland. Until then we must rely on UK data. In 2016, 108?713 knee replacement procedures were done in England, Wales, Northern Ireland, and the Isle of Man. The typical patient requiring knee replacement was aged 69 years and 56 per cent of patients were women. Almost all (99 per cent) of knee replacements were performed in patients with osteoarthritis.

Some 82 per cent of total knee replacements last 25 years

In a nice piece of research just published in the Lancet, Mr Jonathan Evans of the musculoskeletal research unit at the University of Bristol and his colleagues used the UK joint registry data alongside a systematic review of the literature to definitively answer the question: how long will my artificial knee last?

The answer produced a surprisingly optimistic result: some 82 per cent of total knee replacements (TKRs) last 25 years. In other words, if you have a TKR aged 65 you have an 8 in 10 chance of the new joint lasting until you are 90.

It’s important to point out that the longevity of a knee joint does not imply you will be symptom-free for 25 years. One in five patients who undergo TKR for osteoarthritis reports an unfavourable pain outcome; not all these patients undergo revision surgery.

Typical patient

The same team of researchers repeated the study but this time for total hip replacements (THR). The typical patient who had a hip replacement in the UK in 2016 was a 70-year-old woman or a 68-year-old man. Some 90 per cent of hip replacements were carried out for osteoarthritis and 60 per cent of recipients were female.

Due to the poor quality of studies identified in the systematic review, the researchers findings on hips are less certain than for TKR. “Although there is not enough information yet available to calculate exactly how long a hip replacement will last ...we estimate that about three-quarters of hip replacements last 15-20 years and just over half of hip replacements last 25 years in patients with osteoarthritis”, they conclude.

With a growing number of younger, more active patients receiving hip replacements, as well as increasing life expectancy, the more data we have on the average life-span of a THR the better.

But remember, even as these reliable statistics emerge, always ask your orthopaedic surgeon for their personal outcome figures before you decide to go ahead.

mhouston@irishtimes.com