Inflammation After Knee Replacement: How Long + How to Reduce It?

What is knee inflammation in concrete terms?

Knee inflammation is a response from our immune system to an injury or tissue damage. Both of these inevitably occur during surgical procedures!

When a tissue in the body is injured, immune cells like macrophages and lymphocytes:

1. Are recruited to the affected area.
2. Then release chemicals to protect and heal the damaged tissue.

In the process of doing their job, these cells can trigger vasodilation, which is an increase in the diameter of blood vessels to allow the cells to arrive more quickly at the injured area.

These reactions can incidentally lead to mild side effects (but not serious), such as:

• Pain
• Swelling or edema
• Redness
• Heat

Four things you’re likely experiencing with your knee replacement!

Inflammation is an automatic response by the body to repair damaged or assaulted tissues.

How do you know if it’s inflammation and not something else?

People with inflammation sometimes confuse it with infection.

Infection is much rarer and slightly more troublesome.

A knee infection is caused by the presence of bacteria, viruses, or fungi in the knee region.

Often, there is fever or chills as an additional sign when there is an infection, along with unusual fluid drainage from the incision.

If your knee is simply:

• Red
• Warm
• Swollen
• Painful

since the operation, without any other symptoms, it is very likely to be “just” inflammation.

There is no need for additional tests. However, you can always discuss this with your doctor or physiotherapist!

Some people also wonder if inflammation is a symptom of knee replacement rejection.

This is not common; when a knee replacement needs to be revised, it is mainly due to loosening or infection.

And it’s rare.

I sometimes treat people who have inflammation several months or even years after the operation.

Rest assured, it’s rare! Nevertheless, these individuals are often very worried and request additional tests, despite reassurances from everyone (doctors, physiotherapists, surgeons).

I hope that with this type of article, you will be more reassured in such a situation!

Why is there inflammation after knee replacement surgery?

Inflammation is nearly always present after a knee replacement. I’ll explain here:

• Why our bodies react by causing this inflammation when we undergo knee surgery.
• The factors that make inflammation more significant or more impressive in some individuals.

The normal mechanism of the body’s response

Why is a knee that has undergone surgery often the site of inflammation afterward?

To implant the knee prosthesis, the surgeon made an incision in the skin, as well as through various layers and types of tissues beneath the skin (fascia, bone tissue, etc.).

These tissues need to heal to become functional again.

Your body, your immune system (defense system), therefore reacts accordingly, automatically. Inflammatory responses occur at the knee.

This inflammation causes:

• Accumulation of fluids in various layers of tissues. This is why your knee swells after a knee replacement surgery, and edema appears.
• Pain (see my article on pain after knee replacement surgery).
• Redness and warmth at the knee.
• One or more hematomas and bruises.

This inflammation is a necessary step and is beneficial in the medium and long term! It is what allows damaged tissues to be repaired.

Inflammation brings into the damaged knee tissues, through fluids, all the substances needed to help damaged structures heal naturally as quickly as possible.

Inflammation is something very healthy and even healing! It is an automatic response of our immune system that we inherited from our ancestors.

Furthermore, many people already have a slight inflammation before undergoing surgery, due to osteoarthritis (Dainese 2022).

Even if the joint is “repaired” thanks to the replacement, your body needs a little time to recognize this!

Risk factors for prolonged inflammation

Two people of the same age, with the same medical history, the same issue of osteoarthritis, and operated on by the same surgeon, may still experience very different knee inflammation.

Not only can the inflammation be objectively different, but their perception of the inflammation can also vary significantly.

Do we know what causes some people to have more inflammation than others after knee replacement?

Here are the two factors most commonly identified as leading to more knee swelling (which is an indirect measure of inflammation):

1. Losing a significant amount of blood during surgery.
2. Having a high body mass index (overweight or obesity).

Source: Gao 2011

How long does inflammation last after total knee replacement?

To assess the duration of inflammation, various parameters can be considered, such as:

• Skin temperature
• Pain
• Swelling or edema

Duration of inflammation based on skin temperature

A research team evaluated the progression of inflammation in the 90 days following the placement of a total knee replacement (Lohchab 2021).

The study involved individuals who underwent bilateral knee replacement surgery due to osteoarthritis, with an average age of 63 years.

The results are as follows:

• Skin temperature (and thus inflammation) is at its maximum 2 days after surgery.
• It remains elevated until the 6th day after surgery.
• Then the temperature/inflammation decreases significantly for about ten days.
• It continues to decrease more slowly afterward.
• Finally, it returns to preoperative levels on average 3 months after the surgery.

The knee is generally the warmest from the 2nd to the 6th day after the surgery.

Then, the knee’s warmth (and thus inflammation) decreases, returning to normal on average after 3 months.

Duration of inflammation based on pain

We also have data on the evolution of pain in the days and months following knee replacement.

Again, it may appear somewhat complicated at first glance, but it effectively illustrates how pain related to inflammation changes on average:

This diagram indicates that:

• Pain is at its maximum on the first day after surgery (5.8/10 on day 1) and steadily decreases during the first week (down to an average of 4.6 on day 8).
• On the 9th day, pain increases again.
• Then there is a steady decrease in pain. 30 days after the operation, it averages 3/10. (Schindler 2022)

Of course, these are trends.

Most of my patients do indeed follow this type of progression. However, in some, inflammation disappears much faster. For others, it remains elevated for a longer period (several months or more).

If we look at the parameter of pain, there is still inflammation 30 days after the operation.

Read the full article on pain after knee replacement for more information or purchase my ebook ($12) on recovery after knee replacement.

Duration of inflammation based on knee swelling

Swelling is often most pronounced between the 3rd and 5th postoperative days (or the 6th and 8th days) and often affects both lower limbs, but the operated limb is usually more affected (Gao 2011; Loyd 2020).

At 3 months, the volume is still increased by an average of 11% (Pua 2015).

This means that in a significant proportion of people, there is still some inflammation 3 months after the operation.

This inflammation does not necessarily prevent a gradual return to regular activities!

Read the full article on swelling after knee replacement for more details.

Does it last for a shorter time after a partial knee replacement?

It is reasonable to assume that inflammation generally lasts a bit less with a partial knee replacement (PKR).

This is because the surgery takes less time, and fewer tissues are damaged to implant the prosthesis.

To my knowledge, there are no specific studies on inflammation after PKR.

Based on my experience with my patients, people do indeed recover more quickly from a PKR, including inflammation.

But there is a confounding factor: these individuals are generally younger and in better overall health who undergo this type of prosthesis.

How to reduce inflammation after knee replacement?

Pain relief after knee replacement is a broad field of research and concern.

Particularly regarding what doctors and anesthesiologists administer to patients during and in the first two days after the operation, often through intravenous glucocorticoid injections via nerve blocks (Yang 2022; Wu 2020).

However, the goal is not necessarily to stop inflammation, which is a process that helps repair tissues.

The main objectives are:

• To stop or alleviate pain.
• To improve satisfaction.
• To enable rapid remobilization (getting out of bed, walking, bending the knee).

The focus of this article is primarily on what patients or physiotherapists can do in the days and weeks following surgery.

Therefore, I will concentrate on that aspect and not on treatment during or immediately after the operation.