Should you have both knees replaced at the same time?

For most people, no. Having both done together carries a higher risk of serious complications, including a higher risk of dying in the period after surgery, small in absolute terms, but consistently measured across very large studies. It remains a reasonable option for patients who are genuinely fit and well, without significant heart, lung or other medical problems.

Is it common to have both knees done at once?

Less common than it used to be, and becoming less so. In one national analysis of 138,468 bilateral knee replacements, the proportion done in a single operation fell from 19% in 2016 to 7% in 2021. Surgeons have generally become more selective about who is offered it.

Is it better to have both knees replaced at once?

There are real advantages, one anaesthetic, one hospital admission, one rehabilitation period, and lower overall cost. Some studies also find fewer reoperations and fewer wound infections than with two separate operations. Whether those advantages outweigh the higher early risk depends almost entirely on how fit and well you are.

How long should I wait between knee replacements?

If the knees are done separately, the usual interval is a few months. One analysis comparing different intervals found the lowest one-year mortality when the second operation was done between three and six months after the first, with more complications when the gap was shorter than six weeks or longer than six months.

Why do some surgeons offer both knees at once?

Because for a fit, well patient the advantages are genuine, and because some high-volume centres report results as good as staged surgery. The evidence is not unanimous, and reasonable surgeons weigh it differently. What is agreed is that it is not a good option for someone with significant heart, lung or other medical problems.

Should both knees be replaced at once?

Q: What are the risks of a double knee replacement?

Compared with having the knees done separately, doing both at once has been associated with roughly one and a half to two and a half times the risk of dying in the period after surgery, a higher chance of blood clots in the leg, and a substantially higher chance of needing a blood transfusion. The absolute risk of death remains low either way, in one pooled analysis, about 7 in 1,000 for both-at-once versus about 4 in 1,000 for one at a time.

If both knees are worn out, the question comes up quickly: can they be done together and the whole thing got over with at once?

It is a fair question, and there is a genuine answer, though not a simple yes or no. Having both knees replaced in a single operation is usually called a simultaneous bilateral knee replacement, or in plainer terms a double knee replacement. Doing them separately, months apart, is called staged.

The profession has been moving the same way

This is not a matter of individual preference alone. A national analysis of 138,468 bilateral knee replacements found that the proportion done as a single operation fell from 19% in 2016 to 7% in 2021, a substantial change over five years. The patients still being offered it were, on average, younger and healthier than those having the knees done separately.

In other words, surgeons collectively have not abandoned the operation. They have become considerably more selective about who is offered it.

What the evidence actually shows

Several large reviews have pooled the available studies. The picture is consistent on the main point.

The risk of dying in the period after surgery is higher when both knees are done at once. One review of 53 studies covering 572,881 patients found roughly twice the risk. Another, of 42 studies and 567,915 patients, found a similar result for the first year. A third, of 37 studies and 201,479 patients, put it at about one and a half times.

But the absolute numbers deserve equal billing. In that third review, the death rate was about 7 in 1,000 for both-at-once, against about 4 in 1,000 for one at a time. Both figures are low. A doubling of a small risk is still a small risk, and it is still a real one.

Doing both at once is also associated with a higher chance of blood clots in the leg and a substantially higher chance of needing a blood transfusion, three to four times higher across these analyses. Interestingly, the same reviews found no difference in pulmonary embolism, cardiac events, or the likelihood of the knee eventually needing revision.

The argument on the other side, which is real

It would be misleading to present this as one-sided.

Doing the knees separately is not free of risk either. It means two anaesthetics, two hospital stays, two recoveries, and two exposures to everything that can go wrong. Several of the same analyses found staged surgery carried higher rates of deep infection, and one large national study found staged patients had more readmissions and around one and a half times the rate of reoperation.

Cost and convenience are genuine, not trivial. One operation, one admission, one rehabilitation, and appreciably lower total cost.

And at least one large study disagrees with the rest. A series following more than 18,000 patients for an average of over fifteen years found death rates of 0.2%, 0.3% and 0.4% for simultaneous, staggered and staged surgery, no meaningful difference at all. That study almost certainly reflects careful patient selection at a high-volume centre, but it is real evidence and worth knowing about.

Why “you need to be very healthy” is the actual answer

The most useful finding is that the risk is not spread evenly.

When patients were grouped by how many other medical conditions they had, those with a higher burden of illness had markedly more readmissions after simultaneous surgery. Those with few or no other medical problems showed no such difference.

That is the whole argument in one sentence. The question is less “is this operation safe?” and more “is this operation safe for this particular person?” For a fit 62-year-old with no heart or lung disease, the additional risk is modest and the convenience substantial. For someone with diabetes, heart disease and a smoking history, it is a different proposition entirely.

If the knees are done separately, how long between?

There is some evidence on this too. An analysis comparing different intervals found the lowest one-year death rate when the second knee was done between three and six months after the first. Gaps shorter than six weeks, or longer than six months, were associated with more chest and infection-related complications.

In practice the interval is usually decided by how the first knee recovers, and by what suits your life.

What this means for you

If you have arthritis in both knees, the practical position is this:

Most people are better served having one knee done, recovering, and then having the second.
The first knee often improves things more than expected. Some people find the second knee becomes less urgent once the first is comfortable and they are walking better.
Doing both together is a reasonable option for a genuinely fit and well patient who understands and accepts the higher early risk, and who has good support at home for a harder early recovery, both legs are sore at once, which makes getting up considerably more difficult.
If you have significant heart, lung, kidney or metabolic disease, doing both at once is not a good idea, and that view is well supported.

All of the research above is observational: it compares groups of patients who were not randomly assigned, and fitter patients tend to be chosen for the both-at-once operation. That biases the comparison in ways nobody can fully remove. It is the best evidence available, and it should be read as a strong signal rather than a precise measurement.

This is background for a conversation, not a decision that can be made from a webpage. If you have arthritis in both knees and want to talk through which approach suits you, that is a reasonable reason to come in.