How Long Should You Wait Between Knee Replacements?

For most healthy people, the safest gap between two knee replacements is at least three months. The body needs that long to recover from one major operation before facing another. Once the early window has passed, the exact month matters less than how well your first knee has healed and how much the other one hurts. Some people skip the wait entirely and have both knees done in one operation, which trades one set of risks for another.¹

Why The Second Surgery Shouldn’t Come Too Soon

When the knees are done in two separate operations, the second is usually done several months after the first.² The question is how long that gap should be. When the second knee is replaced within 30 or 90 days of the first, the risk of heart attack is about eight times higher than with a longer gap.³ Other heart problems are far more common in that same short window, and blood clots in the leg are almost five times as likely.⁴ Pneumonia is more than three times as likely, and so is needing the new knee operated on again.⁵ Heart risk matters especially because most knee replacement patients are over 60, when hidden heart disease is common.

Heart attacks after knee replacement are uncommon, so even a large multiplier applies to a small starting number. Still, if your surgeon proposes a second operation inside three months, it is reasonable to ask what is driving that timing.

The body is vulnerable in those early weeks. After a knee replacement, white blood cell counts nearly double by the next day, a sign of how strongly the body responds to surgery.⁶ Those counts return close to normal by about two weeks, but some immune cells are still not fully back to baseline.⁷

The 30-to-90-day window is also when most people are still building basic strength and bending range in the first knee, which makes it the worst time to lose the use of the other leg. Booking early often comes from wanting to “get it over with,” an understandable reason but not a medical one.

A short gap is also not the same as having both knees done together. It still means two anesthetics, two hospital stays and two separate recoveries. You take on the stress of a second operation without the main benefit of having both knees done at once, a single recovery period.

Not every risk rises with a short gap. Oddly, a short gap was linked to fewer knee infections and fewer clots reaching the lungs.⁸ But the jump in heart and pneumonia risk outweighs that for most people, which is why surgeons rarely book a second knee within three months.

Does It Matter If You Wait Four Months Or A Year

Past the early window, results look similar. Among people who chose their own gap after the first operation, major complication rates within three months of the second surgery were roughly 3% to 4% in every group.⁹ Another comparison found no real difference in complications or readmissions within 90 days between timing groups.¹⁰ In one hospital using fast-track recovery programs, complications fell from about 29% with a 2-to-6-month gap to 21% at 6 to 12 months and 14% after a year, though the difference could have been chance.¹¹

The fast-track figures are a hint rather than proof. People in these studies mostly chose their own timing, so those who waited longer may have differed in health or recovery, which makes clean comparisons hard.

There are some small advantages to waiting closer to six months. In that same hospital, people who waited 6 to 12 months had shorter hospital stays than those who waited 2 to 6 months.¹² Those with the shorter gap also had a bigger drop in red blood cell levels, a sign of more blood loss or anemia.¹³ If you can wait until around six months comfortably, you may recover a little more easily from the second operation.

Knee surgery causes blood loss that takes weeks to months to replace, and starting the second surgery anemic can mean more tiredness and slower healing. Your surgeon may check a blood count before scheduling the second knee. These findings come from one hospital, so they support leaning toward six months if it’s comfortable, but they don’t make shorter gaps beyond three months unsafe.

In practice, many surgeons suggest a gap of about 3 to 6 months as a starting point, then adjust for your healing, health conditions and wishes. The second date is often set at a follow-up visit once the first knee is doing well.

Your own recovery is a better guide than the calendar. Two people three months out can be in very different shape, one walking without aids and sleeping well, another still swollen and exhausted. If you feel strong at four months and the other knee is limiting you, there is no strong evidence that waiting longer will make surgery safer.

The Risk Of Waiting Too Long

The untreated knee keeps deteriorating. People waiting more than 6 to 9 months for knee surgery saw pain in their other knee get noticeably worse, and the same showed up in those who waited more than a year.¹⁴ In one large group, readmissions within 30 days of the second surgery were about 14% when it was done 7 to 18 months after the first, versus about 9% within 6 months.¹⁵ As the untreated joint gets stiffer and more painful you move less, which can weaken the muscles around that knee and make the eventual operation and rehabilitation somewhat harder.

A bad knee also affects the new one. People shift weight onto whichever leg hurts less, and a painful knee can limit walking and slow therapy for the replaced knee. Uneven strength between legs can make balance and stairs harder.

Some signs say the second knee shouldn’t wait much longer:

Pain in the other knee is now the main thing limiting your walking.
Pain wakes you at night or needs regular painkillers.
You skip exercise the new knee needs because the other one hurts.

Safety data suggest waiting at least three months, while worse pain in the other knee shows up after 6 to 9 months, so the useful window runs between those points. The readmission figures describe a group and can’t say what happens to you.

Having Both Knees Replaced At Once

Doing both knees in one operation gives similar quality of life, pain relief and knee movement to two separate surgeries.¹⁶ People who have two operations often say they feel more prepared for the second one.¹⁷

In practice, both knees are replaced under a single anesthetic, either by one surgical team working on one leg and then the other or by two teams working together, depending on the hospital. The operation runs longer than a single knee replacement, so there is more time under anesthesia and more blood loss in one sitting. You then go through hospital stay, rehabilitation and recovery just once.

The safety picture points in two directions. Pooled results show higher rates of death within 30 days, clots reaching the lungs and blood transfusion with both-at-once surgery.¹⁸ It is also linked to more clots in the leg.¹⁹ But it has lower rates of deep knee infection.²⁰ In one large group, overall infection was about 0.6% after both-at-once surgery versus about 1.4% after two separate operations.²¹ For most complications the absolute difference between the two approaches was 1% or less.²² The higher risks are concentrated in people with other health problems, which is why selection matters so much.

Cost and time favor one operation, but modestly. It means fewer total days in hospital and rehab, about 13 days versus 18 in one comparison.²³ Total charges are higher with two separate surgeries.²⁴ In another U.S. comparison, though, the savings were small, about $643, and 28% of both-at-once patients went to a rehab facility instead of home, versus 4%.²⁵

Recovery looks different with two new knees. Neither leg can be relied on for support in the first weeks, so you’ll likely need more help at home or a stay in a rehab center. Therapy works both knees together, which can be tiring but finishes in one go. With two operations, you recover from the first knee while the second still hurts, so you may favor the better leg during early rehab. One operation means a harder first few weeks but no second surgery, hospital stay or stretch off work.

People with heart disease have higher risks of heart attack, kidney injury and transfusion after knee replacement.²⁶ Both-at-once surgery is therefore usually offered only to people in good general health.

If you’re considering it, ask your surgeon:

Whether your heart, lungs and blood count make you a good candidate.
How the hospital handles blood loss and clot prevention.
What help you’ll need at home, and for how long.

How To Know You’re Ready For The Second Knee

Your first knee should bend and straighten well and support your weight without a walker, though there’s no single test that proves readiness. A practical check is whether you can walk around your home and run errands without a cane and without limping from pain. You should be able to climb a flight of stairs, with a rail if needed, and get up from a chair without pushing hard with your hands. Your surgeon or physical therapist can test your range of motion and strength, so ask for their assessment rather than relying only on how it feels.

Your overall health matters as much as the knee. Energy, sleep and blood counts should be back near normal, since a body still catching up has less reserve for surgery. Blood pressure, diabetes and other long-term conditions should be steady. Any heart, lung or kidney condition should be checked and stable, since these raise surgical risk.²⁷ If you have one, the specialist who treats it may need to review your health before the date is confirmed.

Mental readiness counts too. Preparation programs that explain what to expect and teach relaxation helped people feel calmer and manage pain better,²⁸ so ask whether your hospital offers one. Remembering how the first recovery really felt, including the hard days, helps you plan without dreading or underestimating it.

Your experience with the first surgery is a real advantage. Note what helped with pain, sleep and swelling and repeat it. Set up your home the same way, with a bed downstairs and grab bars if you used them. Expect the second recovery to feel different, sometimes easier, sometimes harder. Arrange help at home, rides and time off work before booking the date.

A few weeks ahead:

Book a check with your surgeon and family doctor.
Ask whether you need blood tests or a heart check.
Keep doing exercises for the first knee right up to surgery.
Line up physical therapy appointments for after the second operation.

Some things are good reasons to push the date back. A cold, infection or dental problem should be cleared up first. Ongoing swelling or pain in the first knee should be checked. And life events that leave you without support at home are a fair reason to wait.