Having Both Knees Replaced: Same Day or Months Apart?

When both knees are worn out, there are two ways to replace them: both in a single operation, or one at a time with a gap of months between. The single operation means one anaesthetic and one recovery, but it carries higher rates of blood clots and other serious complications, so most surgeons reserve it for fitter patients and stage the rest.

I hear from a lot of women whose X-rays show the same thing on both sides. It makes sense: osteoarthritis rarely picks only one knee, and a knee that has been carrying extra load for years while its partner limps along tends to wear faster too. The question that follows is always the same. Do I get it all over with at once, or do I go through this twice? This article sets out what each route involves, what the best pooled evidence says about the risks, and which questions decide it for an individual woman.

Why both knees so often go together

Knee osteoarthritis commonly affects both sides. It is the joint that osteoarthritis most often disables worldwide, and women carry a disproportionate share of it, particularly after about age 50 ¹. The things that drive it, including age, body weight, alignment, family history, and the fall in estrogen around menopause, act on both legs at once.

There is also a mechanical reason the second knee catches up. When one knee is painful, you shift weight toward the other without noticing, and you favour the “good” leg on stairs and getting out of chairs. After the first replacement, the operated leg is protected for weeks while the other does double duty. Many women who planned on one knee find the second is on the table within a year or two.

Having two bad knees does not by itself mean you need two replacements now. Surgery is considered when symptoms are severe and persistent and good conservative care has been tried, and that test applies to each knee separately. The checklist in signs it’s time for a knee replacement works one knee at a time, and it is common for one side to meet it well before the other.

The two routes, plainly

A simultaneous bilateral knee replacement replaces both knees under one anaesthetic. In most cases one knee is done and then the other, in the same session, by the same team. You wake up with two new knees and go through one hospital stay and one recovery.

A staged bilateral knee replacement replaces one knee, lets it recover, and then replaces the other in a second operation. The gap is set by how well the first knee does. In practice a few months between operations is common, and some women leave it a year or more because the first knee went well and the second is tolerable for now.

There is a third, less common version: two operations during the same hospital admission, a few days apart. It is used in some centres but is not widely offered, and the trade offs sit between the other two.

What the evidence says about risk

The most useful single source here is a 2019 systematic review and meta-analysis that pooled 18 comparative studies published between 2001 and 2018, covering 73,617 patients who had both knees done together and 61,838 who had them staged ². Its findings pull in two directions, which is why the decision is genuinely individual.

Simultaneous surgery came out worse on the most serious medical risks. It was associated with higher mortality, more pulmonary embolism (a clot reaching the lungs), and more deep vein thrombosis than staged surgery ². These events are uncommon after any knee replacement, but they are the ones that matter most, and doubling the size of the operation in one sitting puts more strain on the heart, lungs, and circulation in a single go.

Simultaneous surgery came out better on some others. The same analysis found lower rates of deep infection and respiratory complications with the single operation, which makes sense when you count one anaesthetic and one hospital stay rather than two ².

Several outcomes showed no clear difference. Revision, superficial infection, arthrofibrosis (troublesome scar tissue stiffness), cardiac complications, neurological complications, and urinary complications did not differ significantly between the two approaches ². The authors concluded that because both routes have risks and benefits, the choice has to be made in light of each patient’s own needs, and that randomised trials are still lacking.

For the general complication picture after a single knee replacement, including the infection and clot figures that sit underneath all of this, see knee replacement risks for women.

Who tends to be offered the one-operation route

Surgeons generally keep simultaneous replacement for patients they judge most likely to tolerate a longer, bigger operation. Selection policies vary between surgeons and hospitals, but the factors that usually push toward staging are the ones that raise the stakes of a clot or a strain on the heart: older age, significant heart or lung disease, a previous blood clot, higher body weight, and other medical conditions that make a long anaesthetic riskier.

Women who are younger, fit, and otherwise healthy, with severe arthritis in both knees, are the group most often offered the choice. Even then, some surgeons simply do not perform simultaneous replacement, as a matter of practice, and that is a legitimate position rather than a refusal to help.

It is worth knowing that being offered the single operation is not the same as being advised to have it. Ask your surgeon directly how they assess you for it, how many they do, and whether your own health history changes their answer.

What recovery looks like each way

The recovery is where the choice becomes personal, because the two routes feel very different from the inside.

With both knees done together, the first weeks are harder. There is no good leg to push up from, no strong side to lead with on a stair, and no easy way to get out of a low chair. Pain and swelling are present in both legs at once. Some people go to an inpatient rehabilitation unit for a period before going home, depending on the health system and how they are managing. In exchange, the whole process happens once: one stretch of physiotherapy, one return to driving, one period of help at home.

With staged surgery, each recovery is easier, but there are two. You always have one working leg, which makes walking with aids, getting on and off the toilet, and managing a house far more straightforward. The general shape of a single knee recovery applies each time: walking with aids from the first day or so, off them for most women by around 4 to 6 weeks, back to most daily activities by about 3 months, and a final result that can take up to a year. The week by week recovery timeline covers that in detail.

Some women find the second recovery easier because they know what is coming. Others find it harder, because the dread is better informed. Both reactions are common.

How long to wait between staged knees

There is no fixed interval. The second operation is usually scheduled once the first knee has recovered enough to be the leg you rely on through the second recovery: walking without aids, bending usefully, and strong enough to push you up from a chair. For many women that point comes after a few months, and the surgeon will want to see the first knee before booking the second.

Two things tend to set the timing in practice. The first is how the first knee is doing; a knee that is still stiff or swollen is a reason to wait. The second is your own life: when you can arrange help, time off, and someone to drive. Women often choose a season for the second knee as much as a month.

The months between operations are not wasted. Strengthening the thigh muscles of the second leg before surgery helps the same way it did the first time. Exercise reliably reduces pain and improves function in knee osteoarthritis ³, and the exercise plan for knee replacement recovery doubles as useful pre-surgery work for the knee still waiting its turn.

What I would weigh if it were me

I had my right knee replaced at 61, and my left is still my own, so I have not lived through either route twice. What I have done is listen to a great many women who have, and the things they tell me they wish they had weighed are practical rather than medical.

Who is at home? A woman living alone, or caring for a husband or a grandchild, has very good reasons to want one working leg at all times. Stairs at home matter in the same way. So does work: some women would rather take one longer block of leave than two shorter ones. And so does temperament. A few women have told me they could not face going back for the second knee once the first was behind them, and wished they had considered doing both. Many more have told me the opposite: that having one good knee to lean on was what got them through.

None of those preferences override the medical assessment. If your surgeon thinks your heart, lungs, or clot history make the single operation a poor idea, that settles it. But where both routes are genuinely on offer, the practical questions are yours to answer, and it helps to answer them before the consultation rather than in it.

Questions to take to the consultation

• Do you perform simultaneous bilateral knee replacement, and would you offer it to me? Why or why not?
• Which of my health conditions or medicines changes the risk of doing both together?
• If we stage them, which knee goes first, and roughly how long would you expect to wait before the second?
• Would I be likely to need a stay in a rehabilitation unit if both were done together?
• What clot prevention would I have, and for how long?
• How would my recovery plan differ between the two routes?

The questions to ask your knee surgeon cover the broader consultation, and the preparation steps in preparing for a knee replacement apply to both operations if you stage them.

The long view

Whichever route you take, the long-term picture for the knees themselves is encouraging. The pooled analysis found no significant difference in revision rates between simultaneous and staged surgery ², and around 8 to 9 in 10 total knee replacements last 20 years or more according to the large registry analysis by Evans and colleagues ⁴. The decision about scheduling is mainly about getting through the operations and the recoveries safely, not about how long the knees will last afterward.

This article is general information, not medical advice. Whether you are a candidate for one route or the other, and what is safest for you, are decisions for you and a surgeon who can examine you and review your health history.