The answer to “why are my knees hot?” isn’t straightforward.
You see, joint warmth is often caused by inflammation. But, inflammation itself has several possible causes.
Sometimes it’s a natural response of the body.
For example, we use swelling and redness to fight off infection or to recover from a fresh injury.
Other times it can be a sign of an overuse injury, like tendinitis or osteoarthritis.
But, knee warmth is also a symptom in some health conditions that need medical attention, like an autoimmune disease.
It’s a lot to take in. I know. But I’ll make this as simple as I can. Here’s a list of topics you’ll find here:
- Knee injury
- Runner’s knee
- Knee osteoarthritis
- Rheumatoid arthritis
- Tick bite
- Rheumatic fever
- When you should see a doctor
8 causes of warm knee joints
A knee injury
Swelling is a natural response of the body that promotes healing. It’s normal to have a swollen joint in:
- Total or partial tears of the ligaments or meniscus.
- More serious injuries, like a broken bone.
This is normal and expected – the swelling and heat mean your body is healing. They will improve once the injury gets better.
The treatment will depend on the severity of the knee injury. But, it can range from rest and home care to surgery.
Bursitis is the inflammation of your bursa – a fluid-filled sac that reduces friction between your muscles, tendons, bones, and/or skin.
Its placement between those tissues makes it prone to irritation, especially with excessive movement.
Now, knee bursitis is a common form of this injury.
It causes knee inflammation on the affected bursa which will be painful and warm to the touch.
There are several types of knee bursitis, but the most common ones are prepatellar and pes anserine bursitis.
The treatment depends on the cause of the swelling.
If the inflammation happened due to a bacterial infection, you’ll need antibiotics.
If it was caused by excessive friction, you’ll need to rest.
You should do also other treatments to prevent future episodes as the chances of it happening again are high.
This can help: 7 scientifically-backed treatment options for knee bursitis
Patellofemoral pain syndrome (PFPS)
This syndrome is an umbrella term referring to anterior knee pain. It’s also known as “runner’s knee” or “moviegoers knee.”
We use this term when any other knee injury has been ruled out. (1)
It can happen due to inappropriate training, lack of physical activity, or a direct hit on the knee. (1)
An acute episode of PFPS can make your knee feel warm and a little swollen.
But, the main symptom is pain around the kneecap that increases after sitting for a while.
It can worsen after standing up, walking, or climbing stairs.
As you can see, the presentation of PFPS varies wildly from person to person. That’s why it’s best to go to physical therapy to treat it.
This is the wear and tear of the knee cartilage.
It often happens due to aging, but previous knee joint injuries and obesity can speed up this process. (2)
Although some people with osteoarthritis don’t have symptoms, the ones that do feel knee pain that (2):
- Has a gradual onset.
- Worsens with excessive or lack of movement.
- Also causes swelling and stiffness.
Osteoarthritis can’t be reversed, so the treatment manages symptoms and prevents further damage.
For mild cases, the treatment includes strengthening your legs and wearing a knee sleeve to ease the pain during the day.
For moderate to severe cases, the treatment may involve surgery. A joint replacement could improve your quality of life.
And, for people with a BMI >25, one part of the treatment should be a weight loss program.
This will help reduce the excess joint fluid and decrease pain.
Rheumatoid arthritis (RA)
This is an autoimmune disease where the immune system attacks cells on the joints.
This causes inflammation, pain, and stiffness in the affected areas.
Rheumatoid arthritis often affects the joints of the fingers and knees.
It’s more common in women +65 years of age with a close relative with this disease. (3)
During a flare-up, rheumatoid arthritis can make the knees feel hot and swollen.
The treatment involves a special anti-inflammatory medication (anti-rheumatic drugs) and physical therapy.
Losing weight and quitting smoking are also key for preventing future episodes.
Sadly, this disease has no cure. But, early treatment can avoid future complications.
So, please go to the doctor if you have signs of rheumatoid arthritis, which include (3):
- Swelling and/or tenderness in more than one joint.
- Stiffness and fatigue.
- Symptoms are worse in the morning.
Further reading: Ortho vs Rheumatologist – who’s the best doctor for your knee pain?
In this disease, uric acid crystals accumulate in the affected joint – often the big toe. In some cases, it can also affect the ankles and knees.
Gout is a common cause of chronic inflammation among men.
It can also be a complication of other diseases, like diabetes, psoriasis, kidney disease, obesity, and some cardiovascular conditions. (4)
During a flare-up, pain tends to be severe and can wake the person up while sleeping.
The joint often looks red and swollen. It can also feel warm to the touch. Other symptoms include fever and fatigue.
Gout symptoms during a flare-up rarely respond to home remedies.
The flare-ups are best managed with anti-inflammatory medications. (4)
And, they’re best prevented with lifestyle changes, such as (4):
- Avoid alcohol.
- Cut your meat and seafood intake.
- Focus on less processed foods.
This is caused by an infection transmitted by ticks.
Apart from joint pain and swelling, the main symptom is a red, ring-like rash at the site of the bite which is present in up to 80% of cases. (5)
The rash often appears in the first two weeks after the bite. Other symptoms of this disease are like the flu – malaise, headache, fever, muscle pain.
This disease can cause several complications if left untreated.
This includes joint swelling, neurologic issues, and cardiovascular problems. The treatment is mostly antibiotics. (5)
This is an autoimmune disorder that can develop after a streptococcal infection.
It’s more common in children between 5-15 years old living in developing countries. (6)
Symptoms are extremely variable, but joint swelling is present in ~75% of patients.
It’s mostly treated with anti-inflammatories and antibiotics. (6)
When to see a doctor for knee swelling?
Please seek medical attention if:
- You have an underlying condition (like diabetes, cardiovascular issues, psoriasis, etc.)
- You have signs of rheumatoid arthritis.
- You have a fever.
- You injured your knee recently.
- You can’t bear weight on the affected leg.
- You’ve had knee pain for more than 6 weeks.
- Your knee locks or catches.
- You can’t straighten your knee completely.
Your doctor will perform a physical evaluation.
He/she may ask for blood tests and other diagnostic tests when necessary to get the right diagnosis.
Why is my knee swollen and warm?
It could be several things, like:
- A natural response after a knee injury.
- Rheumatoid arthritis.
A doctor will tell you why your knee is swollen and how to treat it.
How are warm joints treated?
The treatment depends on what’s making the joints warm in the first place.
Yet, most treatments include some type of medication, physical therapy, rest, and home care.
Why are my knees so hot after exercise?
Because exercise naturally increases blood flow throughout the body.
If you’re also feeling knee pain after working out, please visit a physical therapist to check what’s going on.
Need help finding a physiotherapist in your area? We can help.
Conclusion: Why is my knee joint warm?
There are at least 8 conditions that can cause knee joint warmth.
Some can mean joint damage if left untreated, like some overuse injuries or a fresh knee injury.
Others show that your body is fighting off an infection, like in infected bursitis.
But, feeling your knee hot can also be a sign of a medical condition. Like rheumatoid arthritis, Lyme disease, or rheumatic fever.
That’s why it’s best to seek medical attention if you don’t know what’s going on.
The doctor will prescribe the best treatment for your needs.
- Bump J M, Lewis L. Patellofemoral Syndrome. [Updated 2021 May 8]. Statpearls. Retrieved on November 2021 from: https://www.ncbi.nlm.nih.gov/books/NBK557657/
- Hsu H, Siwiec R M. Knee Osteoarthritis. [Updated 2021 Jul 25]. Statpearls. Retrieved on November 2021 from: https://www.ncbi.nlm.nih.gov/books/NBK507884/
- Chauhan K, Jandu JS, Goyal A, et al. Rheumatoid Arthritis. [Updated 2021 Oct 7]. Statpearls. Retrieved on November 2021 from: https://www.ncbi.nlm.nih.gov/books/NBK441999/
- Fenando A, Rednam M, Widrich J. Gout. [Updated 2021 Sep 15]. Statpearls. Retrieved on November 2021 from: https://www.ncbi.nlm.nih.gov/books/NBK546606/
- Skar GL, Simonsen KA. Lyme Disease. [Updated 2021 Jul 10]. Statpearls. Retrieved on November 2021 from: https://www.ncbi.nlm.nih.gov/books/NBK431066/
- Wallace M, Lutwick L, et al. Rheumatic Fever. [Updated 2021 Mar 23]. Medscape. Available from: https://emedicine.medscape.com/article/236582-overview