Bilateral Knee Replacement: Both Knees at Once or One at a Time?

Most patients who need knee replacement need it in both knees. Osteoarthritis is rarely a one-sided disease. The question that follows, do both knees get done together, or one at a time, is one that patients ask frequently, and the answer depends on factors that are specific to each individual.

KEY TAKEAWAYS

Bilateral knee replacement means replacing both knees, either in one operation or in two separate procedures

Simultaneous bilateral replacement means both knees in the same anaesthetic session

Staged bilateral replacement means one knee first, recovery, then the second knee, typically at least six weeks apart

Simultaneous replacement has the advantage of one anaesthetic, one hospital stay, and one rehabilitation period

The risks of simultaneous replacement are higher in older patients and those with significant medical comorbidities

Most patients with good general health are suitable for simultaneous replacement; the decision is made jointly with the anaesthetist and surgeon

Why both knees often need replacement

When arthritis affects one knee severely, it nearly always affects the other to some degree. Years of favouring one leg places additional load on the other, accelerating wear. By the time a patient presents for surgery, both knees are often symptomatic, one simply worse than the other.

Treating only the more painful knee and leaving the other significantly arthritic is a reasonable short-term solution, but most patients return for the second knee within one to three years. This reality makes the bilateral question worth addressing early.

Simultaneous bilateral knee replacement

Both knees are replaced in the same operation, under a single anaesthetic.

The advantages are practical and real:

One hospital admission instead of two
One anaesthetic exposure instead of two
One rehabilitation period: both knees recover together
Total time from surgery to full recovery is shorter than two staged procedures
Less overall time away from work and family

The risks are also real:

Simultaneous bilateral replacement is a longer, larger operation. Blood loss is greater. The physiological stress on the body is higher. The risk of blood clots (deep vein thrombosis and pulmonary embolism), cardiac events, and the need for blood transfusion are modestly increased compared to a single knee replacement.

For this reason, simultaneous replacement is generally recommended only for patients who are:

In good general cardiovascular health
Younger than 70 years as a broad guide (though this is not an absolute cutoff)
Not significantly obese
Free from significant cardiac, respiratory, or renal disease
Assessed and cleared by the anaesthetist for a longer procedure

Staged bilateral knee replacement

The more painful or functionally limiting knee is done first. After recovery, typically at least six weeks, the second knee is replaced in a separate operation.

The advantages:

Lower immediate surgical risk per procedure
The patient has one functional knee throughout recovery from the first surgery. This significantly aids rehabilitation
If the first surgery results in any complication, the second can be deferred or planned accordingly
Better suited to older patients or those with medical conditions that increase surgical risk

The disadvantages:

Two separate hospital admissions, two anaesthetics, two recovery periods
The total time from first surgery to full bilateral recovery is longer, typically 12 to 18 months from start to finish
The arthritic second knee continues to cause pain and limit mobility during the first knee's recovery
Overall cost and time burden is greater

What most patients actually experience

In practice, many patients who have simultaneous bilateral replacement describe it as the right decision in retrospect. The combined rehabilitation, both knees working toward the same goal simultaneously, has a logic to it. The physiotherapist works both knees together, and the patient does not have to repeat the entire recovery experience a second time.

Patients who have staged replacement often remark that the second knee is easier. They know what to expect, their general fitness is better from the first rehabilitation, and their confidence going into surgery is higher.

Both routes lead to good outcomes in appropriate patients. The choice is not between a good and a bad option. It is between two good options suited to different circumstances.

How the decision is made

The surgeon and anaesthetist together assess:

Age and general fitness
Cardiac and respiratory health
Blood tests, ECG, and anaesthetic risk assessment
Severity of arthritis in both knees: if one knee is only mildly arthritic, simultaneous replacement may not be warranted
Patient preference, once risks and benefits have been explained

The conversation about bilateral replacement should happen before the first surgery is planned, not after the first knee has been booked. Early discussion allows for proper anaesthetic evaluation and realistic planning.

Questions patients commonly ask

“Is doing both knees together more dangerous?” It places a greater demand on the body in one sitting: more blood loss, a longer anaesthetic and more physiological stress. In a fit patient with a clear cardiac and medical workup, that demand is well tolerated. In older patients, or those with heart, lung or kidney disease, or poorly controlled diabetes, the risk rises and staging is safer.

“How will I manage at home with both knees operated?” You will need someone at home for the first two to three weeks. A raised Western-style toilet seat is essential rather than optional, and a bed on the ground floor helps. Patients who arrange this before admission recover far more comfortably than those who improvise afterwards.

“If I stage them, how long do I wait between the two?” Usually at least six weeks, often three months. The first knee needs to be strong enough to support you while the second recovers. Waiting too long is its own problem, because the untreated knee keeps deteriorating and the good leg does all the work.

“Which knee is operated first if I stage them?” Usually the worse one. It gives the greater immediate relief, and it tells us how you respond to surgery and rehabilitation before we plan the second.

THE BOTTOM LINE

If both knees need replacing and you are in good health, simultaneous replacement is a legitimate and efficient option, one operation, one recovery, less overall disruption to life. If your health warrants caution, staging the procedures is the safer path and leads to equally good results, just over a longer timeline. The decision is made with you, not for you, and it starts with an honest assessment of your overall health.

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