Should I Have Both Knees Replaced at Once?

Arthritis is often worse in one knee but present in both. Once a patient decides on surgery, the next question is usually whether to “get it all over with.” The appeal is clear: one hospital stay, one anesthetic, one stretch of time off work, and one rehabilitation instead of two. The concern is that two knee replacements in one sitting place roughly twice the physical stress on the body in a single day. Patients hear strong opinions both ways from friends and online forums. The evidence supports a more specific answer than either “always” or “never,” and it depends mostly on your general health.

No large randomized trial has compared these two approaches. The evidence comes from national databases, joint registries and pooled analyses of those studies, which are large enough to measure uncommon complications.

The three largest pooled analyses

A 2025 meta-analysis combined 42 studies with 567,915 patients, about 225,000 of whom had both knees done at once.² Compared with staged surgery, doing both knees together carried:

• about 4 times the odds of a blood transfusion
• about 2.4 times the odds of death in the first year
• about 1.5 times the odds of a neurological complication, such as confusion or stroke

It also carried lower odds of joint infection in the hospital, fracture around the implant, and reoperation. In-hospital cost was about $7,000 lower. Function scores and persistent pain did not differ between the groups.

A meta-analysis published this June, covering 53 studies and 572,881 patients, reached a similar picture: higher odds of short-term death (about 2.4 times), leg clots (about 1.5 times) and transfusion (about 4.4 times) with simultaneous surgery, and lower odds of superficial and deep infection.³ An earlier analysis of 29 studies found about 2.2 times the odds of death within 90 days and about 1.7 times the odds of a clot in the lungs (pulmonary embolism) with simultaneous surgery, along with a hospital stay about two days shorter.⁴

Putting “twice the odds” in perspective

Death after knee replacement is rare, so “twice the odds” describes a small number becoming a slightly less small number. In a US national hospital database, in-hospital death occurred in 0.30% of bilateral knee replacements compared with 0.14% of single knee replacements, or about 3 in 1,000 patients compared with about 1 in 1,000.⁵ The same study found that age over 75 was one of the strongest predictors of in-hospital death, with about four times the odds. The risk is not spread evenly. It is concentrated in older patients and those with heart, lung or other medical problems, which is why selecting patients carefully matters so much.

Does doing both at once save money?

Simultaneous surgery is cheaper for the hospital stay, but the total picture is less clear. A single-center US study of 562 patients found that people who had both knees done together were more likely to need a stay in an inpatient rehabilitation facility afterward. Once that cost was added, total costs were nearly identical: about $24,600 for simultaneous and $24,900 for staged surgery. The same study found clots in 5.4% of simultaneous patients compared with 1.4% of staged patients, and transfusions in 15.8% compared with 6.2%.⁶

What this means for you: both approaches give the same long-term result in your knees. The choice is about which set of short-term risks fits your health, and whether you can manage the harder recovery of two new knees at once.

The studies agree on what to avoid and disagree slightly on the best window.

• Avoid less than about six weeks. In a US insurance database of more than 25,000 staged patients, second surgeries done within six weeks of the first had higher odds of major complications and revision than those done later.⁸
• Six weeks to three months was associated with lower 30-day mortality than simultaneous surgery in the Australian national joint registry, which followed more than 36,000 bilateral knee replacements. Revision rates were similar at every interval.⁹
• Three to six months ranked best for one-year mortality and 90-day complications in a 2025 network analysis of 15 studies.¹⁰ An expert consensus panel in 2013 recommended waiting at least three months.⁷
• Beyond six months still had lower mortality than simultaneous surgery, though the same network analysis found more lung and infection complications in that group than in the three-to-six-month window.¹⁰

Many second knees are never done

Staging has a cost that the complication studies do not capture. A Canadian study followed 268 patients who planned staged surgery. About one in five did not have the second knee replaced within two years.¹¹ The most common reasons were a slow recovery from the first knee (43%), improvement in the other knee so that surgery no longer felt necessary (27%), and a poor experience with the first operation (23%). Patients who stopped after one knee had less improvement in their knee scores and lower satisfaction than those who completed both. In practice, patients who stage often wait a long time: in a 2026 study of more than 4,000 staged patients, the average gap between knees was 21 months, and patients who had the second knee sooner reported greater pain improvement a year later.¹²

What this means for you: if you stage the surgery, plan the second knee for about three to six months after the first, once you are walking well and the first knee has settled. Some patients find the other knee improves enough that they never need it, and that is a reasonable outcome.

• None of these studies is randomized. Surgeons already choose younger, healthier patients for simultaneous surgery. That selection should make simultaneous surgery look safer than it would be for everyone, which means the true extra risk in an unselected group may be higher than these studies show. It also means the risk for a carefully selected patient may be lower.
• The staged group has a built-in advantage. A patient who has a heart attack or dies after the first knee never has the second one, so that event may not be counted as a staged-surgery complication. The authors of the June meta-analysis note this could make staging look safer than it is.³
• Much of the data is old. Many studies include surgery from the 2000s. Blood management, clot prevention, anesthesia and rapid-recovery protocols have improved since then, and the transfusion gap in particular is likely smaller today.
• The August BMI study is a database study. It relies on billing and record codes, not detailed review of each patient, and cannot account for every reason a surgeon chose one approach over the other.¹ Its findings are a useful signal, not a rule.