My knee is swollen and hot to the touch – What’s the Cause and Treatment?

my knee is swollen and hot to the touch, and picture of swelling of the knee

Is your knee swollen and hot to the touch, and you’re wondering why and what you can do about it?

Thousands of people face this problem every day. Sometimes it happens for no apparent reason, and other times it’s due to surgery, an injury, or a fall.

It can be a source of many questions and concerns, and that’s why, as a physical therapist, I’m here to answer the most frequently asked questions about this issue. My hope is that this information will help you feel more at ease and find simple and practical steps to take.

At the end of the article, you’ll find references to international scientific publications that I relied on to supplement my professional experience.

Still have questions after reading this article? Feel free to leave a comment below!

Last update: May 2023
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Summary
  • Symptoms of a swollen and hot knee
    • Swollen, hot, and painful knee
    • Red, swollen, and warm knee
    • Swollen and hot knee without pain
  • What are the common causes of a swollen and hot knee?
    • Swollen and warm knee after fall, injury, or accident
    • Swollen knee after surgery
  • Swollen and hot knee for no apparent reason
    • Swollen knee after skiing, running, snowboarding, standing
  • Why does my knee feel hot and swollen?
  • What to do when you have a swollen and hot knee?
    • When to consult a doctor or physiotherapist?
    • How to reduce knee swelling?
      • List of possible treatments
      • My recommended approach
      • Recommendations from rheumatologists and surgeons
  • What is better for swollen knee ice or heat?
  • Is hot tub good for swollen knee?

Symptoms of a swollen and hot knee

Wondering about your symptoms is already a good way to see things more clearly.

Here’s a list of symptoms that can be felt when you have a swollen knee.

  • Swelling = edema: these words refer to the same phenomenon. A knee with a larger diameter than usual. Swelling sometimes extends down to the foot and only affects the right or left knee, or both.
  • Redness and warmth in the affected area. These two phenomena are often associated when you have a swollen knee.
  • Pain or stiffness when moving the knee, or even at rest. I’ll go into a little more detail on the pain.
  • Sensation of tearing or cracking when moving
  • Instability or weakness of the knee: you feel like it’s giving out when you walk or go down stairs, or it actually gives out?
  • Difficulty bending (flexion) or extending (extension) the knee. The fluid prevents the joint from moving well. It’s purely mechanical, the fluid is incompressible. There’s no need to force it, the flexion will return when the swelling goes away.

Swollen, hot, and painful knee

Let’s focus a little more on the pain that is sometimes associated with a swollen, warm knee.

It can be localized anywhere:

  • on the side of the knee;
  • around the patella;
  • anywhere;
  • behind the knee; etc.

Here’s the type of pain you may feel.

  • A rather inflammatory type of pain. It is often associated with a red and warm knee. Symptoms may worsen in the second half of the night. And on the contrary, be less strong when moving.
  • A rather mechanical type of pain. The pain will be more intense during activity: when walking or doing sports, or when bending or extending the knee. It will tend to calm down at rest.
  • Of course, you can also have both mechanical and inflammatory pain at the same time.

The fact that you have pain is not a sign of seriousness in itself.

Red, swollen, and warm knee

So you have a swollen, warm knee that’s often also red. The redness is caused by the blood vessels in the area dilating.

Sometimes blood vessels dilate in response to inflammation to help transport the nutrients and immune cells needed for healing.

So swelling can actually be a good thing, as the fluid that accumulates and triggers the swelling is there to bring the nutrients needed for tissue repair.

Swollen and hot knee without pain

Did you know that a knee can be swollen and warm without any pain? Pain is a complex phenomenon that can be triggered not just by physical or biological factors, but also by cognitive and environmental ones.

Here are some situations in which you can have a swollen, warm knee without pain:

  • Osteoarthritis (20 to 60% of people with knee osteoarthritis have no pain)
  • Infection
  • Allergic reaction
  • Muscle injury or strain without immediate pain
  • Circulation problem

What are the common causes of a swollen and hot knee?

What are some common causes of a swollen, warm knee? In the vast majority of cases, it’s due to an accumulation of fluid in the knee joint. This fluid can be of two types:

  • Blood (hemarthrosis). This often happens after an accident or a blow, but sometimes it’s due to a simple inflammation.
  • Synovial fluid (synovitis or synovial effusion). This fluid is present in all joints all the time. It helps the joint slide and move smoothly. But sometimes, it’s produced in greater quantity, causing swelling as it accumulates in the joint.

When an injury or inflammation occurs, the walls of the blood vessels can become more permeable. This means they allow more fluid to pass into the joint from the vessels, leading to an accumulation of fluid and swelling.

picture of swollen knee with hemarthrosis
Left knee hemarthrosis (blood in the joint). Source: Iakovou 2020

Swollen and warm knee after fall, injury, or accident

Did you have a hit on your knee? Did you twist your knee while playing sports, slipping, or falling?

Here are the most common causes of knee swelling in these cases.

Sometimes, a simple interview and examination may suffice to diagnose the problem. Sometimes, additional tests, such as an X-ray, may be necessary.

Swollen knee after surgery

Any surgery under local or general anesthesia can cause knee swelling. Especially:

  • Arthroscopy (even a simple infiltration, which is not surgery);
  • Reconstruction of the anterior cruciate ligament;
  • TTA (transposition of the anterior tibial tuberosity);
  • Unicompartmental or total knee replacement;
  • Meniscus surgery.

💡 Read my article on swelling after knee replacement surgery.

swollen hot knee after knee replacement
At the top, a swollen, warm, and red knee (under the bandage) after surgery (knee replacement)

Swollen and hot knee for no apparent reason

You have not had any hits, accidents, or surgeries, and you think your knee is swelling “for no reason.” At least, without an easily identifiable reason?

Here are some of the many possible causes of this swelling in this context.

  • Tendinopathy or tendinitis. One or more tendons of muscles that insert on the knee joint are inflamed. This is generally more related to movements repeated too closely or intensively, or overexertion. The most common knee tendinopathies are:
    • Patellar tendinitis (also called jumper’s knee)
    • Pes anserinus tendinitis
    • Iliotibial band syndrome (ITBS)
    • Quadriceps tendinitis
  • Patellofemoral syndrome.
  • Knee algodystrophy.
  • Bursitis.
  • An infection.
  • Gout.
  • An allergy.
  • Osteoarthritis or arthritis.
  • A popliteal cyst. One often has a sensation of a lump behind the knee.
  • A tumor (rare ++).
swollen knee picture
A knee swelling in a child without any accident or impact. It was a benign hemangioma. Picture: Choudhari 2014

Swollen knee after skiing, running, snowboarding, standing

If you’re experiencing knee swelling after skiing, running, snowboarding, or standing for long periods, there could be a few reasons why.

  • One possibility is that your knee muscles are working overtime and causing inflammation, which can lead to swelling. This is often referred to as an overuse or repetitive strain injury.
  • Another possibility is that you may have experienced a traumatic injury to the knee joint, such as a sprain, strain, or tear, which can also cause swelling.
  • In some cases, swelling of the knee may be due to an underlying medical condition, such as arthritis or bursitis.

To prevent knee swelling from overuse, make sure to gradually increase the intensity of your activity over time.

Why does my knee feel hot and swollen?

You think: my knee is swollen and hot to the touch… How to know why?

Here’s a list of questions that can help you determine the possible cause of your knee swelling.

Of course, seeking advice from a healthcare professional (physio, physician) who is accustomed to seeing these types of problems on a daily basis can lead to a more accurate diagnosis.

  • When did the swelling (and any other symptoms) appear?
  • Did it happen after something specific like a fall, impact, sports activity, change in shoes, or an increase in training load?
  • If there is pain, does it occur when doing something or when doing nothing?
  • Is it worse at night?
  • What other symptoms do you have?
  • Have you ever had this problem or a similar one before, and in what context?
  • Do you feel like the knee is swelling more and more, stable, or decreasing?
  • Do you have any medical conditions (arthritis, rheumatic disease, etc.) or physical conditions (overweight, muscle weakness) that could partially explain this swelling?

After answering these questions, revisit the part of the article dedicated to the common causes of knee swelling. This may give you some clues.

Guide for diagnosing knee edema in professionals, available in English. The first criterion is whether the swelling follows a trauma or not, with an indication of whether or not aspiration is recommended by this team of orthopedic surgeons.
Guide for diagnosing knee edema in professionals. The first criterion is whether the swelling follows a trauma or not, with an indication of whether or not aspiration is recommended by this team of orthopedic surgeons. Source: Jun Nian 2022

What to do when you have a swollen and hot knee?

At this point, you should have a better understanding of the origin of why your knee is swollen and hot to the touch.

Let’s now look at what you can do if this swelling is bothering you.

When to consult a doctor or physiotherapist?

Have you not yet consulted a healthcare professional for this problem? Have the information in this article or others you found online not been enough to reassure you?

In this case, you can make an appointment with your primary care physician. You will then have a more personalized opinion on the problem you are facing.

Have you already consulted a healthcare professional who has reassured you about the cause of your knee swelling?

In this situation, some people are tempted to seek other opinions until they find a professional who identifies a specific cause and treatment.

This is what is called “medical wandering” or “diagnostic wandering”. There is a whole field of research devoted to this phenomenon.

Another approach to this situation is to trust the first opinion you received. This is personally the option that I choose most often.

Whether the discomfort is significant or not, you can decide to wait a few weeks before seeking another opinion. To see how things evolve.

Because seeking another opinion is not insignificant: it can cost you time, anxiety, and money. Without any guarantee of a different opinion or an opinion that will better meet your expectations.

In addition, the professionals you consult for another opinion may be tempted to propose a “solution” or “treatment” at all costs to alleviate your distress.

Even if they are not really convinced of the effectiveness of this treatment. Because sometimes it’s easier and quicker to “propose something” rather than reassure and say to wait.

This is something that I observe on a daily basis as a physical therapist. Particularly in the case of lower limb edema, whether related to surgery or disease.

Consulting one or more healthcare professionals for diagnosis and treatment is possible. But getting multiple opinions is not always relevant.

How to reduce knee swelling?

In some cases (such as rheumatic diseases like rheumatoid arthritis), a specific treatment may be prescribed, which can reduce or eliminate the swelling.

However, regardless of the cause of the swelling, the methods used to treat it remain the same.

There are countless treatments or home remedies suggested for combating knee swelling. Some are evaluated in clinical studies on healthy or sick adults, while others are not.

List of possible treatments for swollen hot knee

Here’s a summary of treatments that are often recommended by professionals:

  • Wearing compression stockings: This can reduce the volume of the lower limbs in healthy people who wear them, as well as after arthroscopy, but not after knee replacement.
  • Applying cold or cryotherapy.
  • Having pressotherapy sessions.
  • Practicing manual lymphatic drainage or other manual or device-based massages.
  • Using shock waves or ultrasound.
  • Wearing a brace or orthosis.
  • Elevating the leg (with the foot higher than the heart).
  • Avoiding prolonged standing.
  • Walking as much as possible.
  • Taking anti-inflammatory medications (NSAIDs).
  • Adopting a diet rich in natural anti-inflammatory and antioxidant foods.
  • Undergoing a joint fluid aspiration (arthrocentesis) or injection (corticosteroids, hyaluronic acid, etc.).
  • Having surgery.
  • Applying essential oils or ointments.
  • Reducing salt intake.

How do you choose among these (incomplete) options? Do you need to try each one individually or try several at the same time?

My recommended approach as a physical therapist

Here’s how I usually reason for myself and my patients in these situations where there are many possible treatments, but few seem to stand out significantly.

I choose based on these four criteria:

☑️ Maximum effectiveness (theoretical / empirical).
☑️ Minimum side effects.
☑️ Minimum cost (in time, energy, money).
☑️ Minimum dependence on a third party or equipment.

For example, I automatically eliminate surgical procedures such as joint fluid aspiration: there’s no long-term guarantee that the fluid won’t return to the joint, the procedure is costly, and there’s a risk of side effects like infection.

I also eliminate shock waves because the theoretical mechanism of action on swelling is inconsistent, and it requires visiting a professional equipped or equipping oneself with expensive equipment.

Thus, my assessment of each of the treatments listed (and the scientific literature devoted to them) leads me to prioritize this approach in case of knee swelling:

  • Seek one (and only one) medical advice to refine the diagnosis if the swelling lasts for more than a few days and worries you.
  • Wear compression stockings if it’s not summer and there are no contraindications and they’re well tolerated (physical therapists can prescribe compression stockings).
  • Elevate the foot when possible during the day.
  • Avoid standing still for long periods of time.
  • Walk regularly throughout the day.
  • Have confidence that things will gradually return to normal, no matter what you do.

Recommendations from rheumatologists and surgeons

You may be surprised by my recommendations. Perhaps you have been recommended one treatment or another. Often:

  • Physical therapists will recommend exercises, shock waves, pressure therapy, etc.
  • Rheumatologists will recommend medications or injections.
  • Surgeons will recommend aspiration if it does not improve.
  • Osteopaths will recommend osteopathy.

What do they all have in common? Each healthcare professional will recommend something they themselves practice.

This is one of the reasons why surgeons and rheumatologists from more than 10 countries came together to establish recommendations for the management of acute knee swelling (Landewe 2009).

study on hot and swollen knee treatment
What a group of ten rheumatologists and surgeons from different countries recommend after analyzing the scientific literature

Here’s what they recommend in terms of treatment:

  • Unload the swollen lower limb (for example, by using crutches)
  • Use a brace
  • Apply compression
  • Apply cold therapy
  • Use simple analgesics and anti-inflammatory drugs (NSAIDs) if not contraindicated

And that’s it! Note that some of the recommendations may not seem appropriate for swelling, but rather for pain.

What is better for swollen knee ice or heat?

When dealing with a swollen knee, it is generally recommended to use ice rather than heat. But there can be exceptions. For example, some people may find relief by applying heat to their thigh, as it relaxes them.

Ice can help reduce inflammation and pain by:

  • constricting blood vessels;
  • and decreasing blood flow to the affected area.

Heat, on the other hand, can increase blood flow and may worsen swelling.

The ice should be wrapped in a towel or cloth to prevent direct contact with the skin, which can cause ice burns.

If the cold doesn’t relieve your pain when you apply it, there’s not much point in continuing to use it.

Is hot tub good for swollen knee?

From a theoretical perspective, a hot tub may help alleviate swelling in a knee.

  • The heat from the hot tub may cause blood vessels to dilate, which could increase blood flow to the knee and improve circulation. This increased blood flow may help reduce swelling by removing excess fluid and waste products from the knee.
  • The warm water and buoyancy of the hot tub could help reduce the weight and pressure on the knee, which could further decrease inflammation and swelling.
  • The warm water may also help relax the muscles and joints around the knee, reducing stiffness and pain.

There is no empirical data about this. I don’t think we can expect a truly significant effect from hot tub. And it can be complicated to implement. That’s why I don’t list it in my recommended treatments for a swollen and warm knee.

***

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 ðŸ“š SOURCES

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Iakovou I, Kotrotsios D, Michailos K, Sachpekidis C. Radiosynovectomy is a safe and an efficient alternative in the treatment of chronic, recurrent knee hemarthrosis. World J Nucl Med. 2020 Jan 17;19(2):165-167. doi: 10.4103/wjnm.WJNM_43_19. PMID: 32939210; PMCID: PMC7478294.

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Treatment

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photo de nelly darbois, kinésithérapeute et rédactrice web santé
By Nelly Darbois

I love to write articles that are based on my experience as a physiotherapist and extensive research in the international scientific literature.

I live in the French Alps 🌞❄️ where I work as a physiotherapist and scientific editor for my own website, where you are.

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