Will I Need My Other Knee Replaced?

One of the most common questions after a knee replacement is whether the other knee will eventually need surgery too. The honest answer is: it depends. Some patients have arthritis in both knees and eventually have both replaced. Others have one bad knee and never need surgery on the other.

The most important factor is why the first knee needed replacing. Conditions that affect the whole body — like osteoarthritis, rheumatoid arthritis, or inflammatory arthritis — often involve both knees. Problems caused by a prior injury, fracture, infection, or surgery may be limited to a single knee.

It depends on the diagnosis

The reason you needed a knee replacement is the single best predictor of whether the other knee will eventually need one too. Common reasons patients undergo knee replacement include:

Some of these commonly affect both knees, while others are usually limited to one side.

Which conditions tend to affect both knees?

A useful way to think about it is whether the cause is systemic (affecting the whole body) or localized (affecting only one knee).

More likely to involve both knees

Osteoarthritis. The most common reason for knee replacement. Because aging, genetics, weight, alignment, and cartilage wear affect both legs, many patients eventually develop arthritis in both knees.

Rheumatoid and inflammatory arthritis. Driven by inflammation throughout the body, these conditions commonly affect both knees.

Significant bow-legged or knock-kneed alignment. When both knees share the same alignment issue, arthritis may develop on both sides over time.

Usually limited to one knee

Post-traumatic arthritis. Arthritis that develops after a fracture, ligament injury, or major trauma is often confined to the injured knee.

Arthritis after prior surgery. A knee that has had previous surgery may develop arthritis independently of the opposite side.

Localized osteonecrosis. Certain forms of osteonecrosis can affect only one knee.

Of course, patients can have a combination of these factors — which is why every situation is unique.

What knee X-rays show

Whenever I evaluate a patient for knee arthritis, I obtain weight-bearing knee X-rays. These let me assess:

Often, while we're discussing the painful knee, we discover the opposite knee already has some degree of arthritis too. That information is helpful — but it doesn't automatically mean surgery is needed.

The X-ray guides — but how you feel decides

This is one of the most important concepts in knee replacement. I have patients whose X-rays show severe bone-on-bone arthritis in both knees, yet only one knee actually bothers them. I also have patients whose films look only moderately arthritic but whose pain and limitations are severe.

That's why I never recommend surgery based on X-rays alone. The decision comes down to:

How I approach a patient with arthritis in both knees

My general approach is straightforward:

1. Replace the knee causing the greatest pain and limitation.
2. Allow that knee to recover.
3. Monitor the opposite knee over time.
4. Make future decisions based on symptoms and function.

If both knees are severely arthritic and significantly affecting quality of life, I generally recommend staging the surgeries about four weeks apart. This lets patients recover from the first operation before the second, while still addressing both knees in a relatively short time frame.

Can we predict when the other knee will need replacement?

Not accurately. Some patients have arthritis in the opposite knee that stays stable for years; others progress within months. Even when the X-ray suggests a second replacement is likely at some point, it's impossible to predict exactly when symptoms will become severe enough to justify it. Rather than guessing, I prefer to monitor the knee and let your symptoms guide the timing.

The bottom line

Having one knee replaced does not mean you'll automatically need the other replaced. Your diagnosis helps us estimate the likelihood; your quality of life determines the timing. Some patients eventually have both knees replaced — others never need surgery on the opposite side. The goal isn't to replace a knee because an X-ray looks bad; it's to replace a knee when it's keeping you from the life you want to live.

If knee arthritis — on one side or both — is limiting your life, schedule a consultation with Dr. Harb to talk through your options and what knee replacement recovery looks like.