How Long Does a Knee Replacement Last? (What Studies Say)

What is the average lifespan of a partial knee replacement?

To determine how long a partial knee replacement (= unicompartmental knee arthroplasty) lasts, I don’t rely solely on my experience as a physical therapist.

Even though I have conducted dozens of rehabilitation sessions for this type of knee replacement, I don’t see these patients long-term often enough. Moreover, there are studies that follow operated individuals over several decades.

So, I rely on data from clinical studies!

Here are the most reliable and recent data I found on the subject, and they are very reassuring:

7 out of 10 people who received a unicompartmental knee arthroplasty keep their prosthesis for more than 25 years.

Lancet 2019

These figures are based on the follow-up of 742 people who underwent partial knee replacement surgery for knee osteoarthritis, in four different countries.

What is the average lifespan of a total knee replacement?

Again, to inform you about the lifespan of a total knee prosthesis, I prefer to rely on clinical trials conducted on the subject.

These figures also come from the same publication in The Lancet, and they are even more reassuring!

8 out of 10 people who received a total knee prosthesis keep their prosthesis for more than 25 years.

Lancet 2019

These figures are based on the follow-up of 6,490 people who underwent total knee prosthesis surgery for knee osteoarthritis, in ten different countries.

However, there are other reasons for revision surgery of a prosthesis beyond simple “wear” [Stone 2022]. The three main reasons are:

1. aseptic loosening, most often due to improper positioning of the replacement,
2. infection,
3. and unexplained pain.

What factors influence the lifespan of a knee replacement?

It is difficult to clearly identify the factors that influence the risk of needing knee reoperation after receiving a total or unicompartmental prosthesis.

Here are the factors for which we have the most evidence in the international scientific literature. I only mention modifiable factors, which we can partly influence at an individual level.

The later you undergo surgery, the lower your risk of needing another operation

This makes sense: people who receive a knee replacement at age 90 are much less likely to require reoperation than those who get one at age 45.

But here is more precise data on this subject [Stone 2022].

• For people aged 46 to 50 at the time of their total knee replacement, a little more than 1 in 5 will need reoperation on that knee in their lifetime.
• This risk decreases steadily with age.
• For people aged 90 to 95 at the time of the surgery, barely more than 1 in 100 will need another operation in their lifetime.

The same applies to unicompartmental knee replacement, as shown in the graph below [Kennedy 2020]:

Does the risk of revision surgery increase if you are obese?

Including obesity as a modifiable risk factor is delicate because I know many people who wish to lose weight, take steps to do so, and still struggle.

However, I think it’s important to discuss this here because some surgeons refuse to operate on individuals until they have lost a certain amount of weight.

Often, this is due to the risk of complications during surgery, particularly related to anesthesia.

But does obesity also increase the risk of knee replacement revision? The data on this are contradictory:

• Two scientific publications find that people who are obese at the time of knee prosthesis implantation are at a higher risk of needing reoperation than those who are not obese.
• Three scientific publications find that obese individuals are not more likely to need knee reoperation than others.

How can you tell if a knee replacement is worn out?

Some people have had a knee replacement for over 25 years without experiencing significant discomfort or pain: great!

Even if you’ve had your knee prosthesis for a long time, there’s no need to worry if you’re not experiencing any discomfort or pain.

However, knee pain is relatively common after knee replacement surgery: 1 in 5 people who have had a total knee replacement for arthritis report unfavorable pain outcomes post-surgery.

Experiencing knee pain alone doesn’t necessarily mean the prosthesis is damaged, especially within the first 10 years.

There are no highly specific clinical signs indicating a damaged replacement. Only imaging tests, following an initial assessment by a doctor, can confirm prosthesis wear.

What should you do if you suspect your replacement is too worn out?

If you’ve been experiencing increased pain and discomfort in your prosthetic knee for several weeks, you can discuss it with:

• Your general practitioner
• Your physical therapist
• Another trusted medical professional, such as a sports doctor or rheumatologist

Your healthcare professional will ask questions, examine you, and possibly refer you to another specialist (orthopedic surgeon) or recommend further tests (X-ray or MRI). They might also reassure you that the issue could be minor and temporary.