A hot, swollen knee joint is a common clinical condition encountered in the emergency department and elective orthopaedic and rheumatology clinics.
Sometimes doctors find it difficult to manage and properly treat until different tests and examinations are done to identify the actual cause.
As a diagnostic radiographer, I rely on my professional knowledge as well as my research in scientific studies dedicated to the causes and treatment of swollen knees.
You will find all the sources I rely on at the end of the article.
Happy reading!😀 and feel free to ask questions in the comments or share your own experience.🙏
Last updated: December, 2025. Written by Juliet Semakula, a diagnostic radiographer.
▶️What are some of the symptoms of a swollen and hot knee
Most patients do wonder about their symptoms, which is a good way to see things more clearly.
Here are some of the common symptoms that can be felt when you have a swollen knee:
🔴Painful knee to ache or be tender to the touch.
🔴Knee stiffness and difficulty moving the joint or hard to straighten or bend your knee completely.
🔴Redness around the skin of the knee.
🔴The knee joint may feel heavy.
🔴You may find it difficult to bend or straighten the knee due to swelling and stiffness.
🔴The skin around the kneecap may look swollen or puffy.
🔴You may be unable to put full weight on the leg due to pain.
🔴Some people have a high temperature and feeling hot and shivery which is a sign of infection.
▶️What are the two common causes of a swollen and hot knee
In most people I saw in x-ray with swollen knees, causes are due to an accumulation of fluid in the knee joint.
This can be of two types:
1️⃣Synovial fluid is composed of an ultrafiltrate of blood plasma which provides nourishment to surrounding cartilage. An excess of this fluid, known as effusion, can cause swelling, pain, and stiffness
So, when we take an x-ray and an effusion is seen, normally this is one of the signs used to diagnose conditions like arthritis, gout, or infection.
2️⃣Blood (hemarthrosis) is the medical term for blood within a joint space, causing pain, swelling, stiffness, and reduced movement, often caused from injury (like ACL tears) or bleeding disorders
X-ray image showing Joint fluid: suprapatellar bursa. Note the distended suprapatellar bursa (arrows) compressing the anterior femoral fat pad. It blends with the quadriceps tendon making the tendon appear thicker than normal
Image from: Drzezo in musculoskeletal imaging.
▶️Painful hot swollen knee
I have seen people complaining of swollen, painful and hot knees, which are normally localised around the patella, on top and behind the knee.
Let’s focus a little more on the pain that is sometimes associated with a swollen warm knee.
This kind of Knee pain can be caused by injuries or a medical condition
A hot knee can be typically caused by inflammation from injuries. When you have had an injury, your knee may swell caused by excess fluid build up in or around the joint, stemming from injuries, overuse, or underlying medical conditions
Some people I have seen with painful hot swollen knees normally come to x-ray with some of these conditions.
♦️A fracture
♦️Ligament or meniscus tears.
♦️Bursitis
♦️Inflammation of a tendon in the knee
♦️A sign of infection.
♦️Hemarthrosis
♦️Osteoarthritis flare
♦️Injury.
♦️A flare-up of an inflammatory condition like gout or septic arthritis
♦️Most of the time patients are not even able to put weight on the leg.
A case study of a painful hot swollen knee
A woman in her 90s presented to the emergency department with a medical history of respiratory infections, knee osteoarthritis, and gout (for which she was taking allopurinol). She had no joint replacements and no trauma involved (Han 2022)
She had a high temperature and a painful hot swollen knee.
On examination revealed an acutely warm, tender, swollen and painful left knee with moderately limited flexion and extension and an effusion.
Tests such as x-ray, blood tests and inflammatory markers were done, diagnosis was acute gout which is a painful form of inflammatory arthritis caused by the sudden deposition of urate crystals in a joint, leading to rapid-onset pain, swelling, redness, and warmth.
Learning points from this case study:
If your knee is painful, swollen and hot, it is important to see a doctor to rule out septic arthritis as this can be an emergency and to find the right diagnosis.
Source: Han 2022.
The inflammatory type of pain is often associated with a red warm knee; symptoms may worsen in the second half of the night.
And mechanical types of pain can be more intense during activities such sports, bending and extending the knee.
This does not mean that pain is a sign of seriousness but always get it checked.
▶️Swollen knee after surgery
Any surgery performed under local or general anaesthesia can cause knee swelling. For example, knee replacement, arthroscopy, anterior cruciate ligament reconstruction
Swelling after knee surgery is normal and part of the healing process, though it can last for months.
However sometimes you may experience infection which is very rare. Rates of prosthetic infection in orthopaedic surgery continue to fall and the rate of infection in total knee replacement ranges between 0.8% and 1.9% (Lotz.2019)
Some people who have had infection after surgery normally can set in immediately postoperative, within days, early, within 3 months of joint replacement.
Or it can be delayed between 3 and 12 months after surgery or late, after more than 12 months since surgery
Early infection usually results from a more-virulent organism such as Staphylococcus aureus, while delayed infections usually result from less-virulent organisms such as coagulase-negative Staphylococcus (Moran, 2007)
People who come to hospital suspecting of infection normally have the following Symptoms:
♦️knee pain and warm to touch
♦️Swelling.
♦️Erythema.
♦️Stiffness and systemic features of sepsis.
If you have Calf and leg swelling this may occur due to inflammatory response, but deep vein thrombosis (DVT) is associated with major joint replacement surgery and has also been reported in conjunction with septic arthritis of the knee (Rafailidis,2007)
♦️Read an article on swelling after knee replacement.
▶️Red, swollen, and warm knee
A red, swollen, and warm knee can indicate various issues, ranging from minor inflammation to serious infections.
The redness on a swollen knee is caused by the body’s inflammatory response to an injury, infection, or underlying condition, which leads to increased blood flow to the area.
Sometimes blood vessels dilate in response to inflammation to help transport the nutrients and immune cells needed for healing.
However, this swelling can 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
Some people do have a swollen, hot knee without pain, this could be due to an underlying condition, cognitive and environmental factors
♦️Arthritis (20% to 70% of people with knee osteoarthritis or rheumatoid arthritis have no pain).
♦️Infection
♦️Allergic reaction.
♦️Circulation problem.
♦️Muscle strain with immediate pain.
source: Reed 2012
It’s important to see a doctor to get a proper diagnosis, as these conditions can cause inflammation, and you should also be evaluated for a possible infection, which is a serious but less common cause of a hot, swollen knee, especially if other symptoms like a fever are present.
▶️Swollen and hot knee for no apparent reason
A hot and swollen knee without a clear injury can be caused by inflammation caused by:
➡️Bursitis: Inflammation of the fluid-filled sacs that cushion the knee. It can be caused by overuse or occur without a clear reason.
➡️Tendonitis: Inflammation of a tendon, which can be a result of repetitive strain.
➡️Osteoarthritis and rheumatoid arthritis: these conditions can cause joint pain, stiffness, and swelling without pain
⚪Runner’s knee
⚪ Knee bursitis
⚪An infection.
⚪Gout
⚪Tumour
⚪Iliotibial band syndrome
⚪The list is endless
▶️Swollen knee after skiing, running, snowboarding, standing
A swollen knee after physical activity like skiing, running, or snowboarding is a common thing.
The swelling (medically termed effusion) is the body’s response to inflammation or injury.
If the swelling is rapid, severe, or you cannot bear weight, seek immediate medical attention immediately because this can be a ligament tear or fracture.
Here are some of the potential causes.
⚪Ligament Injuries such as ACL/MCL tears/sprains: These are very common in snow sports due to twisting forces and can cause immediate swelling, pain, and a feeling of instability or a “pop” at the time of injury.
⚪Meniscus Tears: Damage to the C-shaped cartilage shock absorbers in your knee can result from sudden twists and lead to swelling, stiffness, and a locking sensation
⚪ Patellofemoral Pain Syndrome (Runner’s Knee): This overuse condition causes pain around or behind the kneecap and is common in runners, skiers, and snowboarders.
⚪Bursitis: Inflammation of the fluid-filled sacs that cushion the joint can cause pain and swelling, often due to repetitive pressure or impact.
⚪ Fractures: A hard fall or impact could cause a bone fracture, which results in severe pain and significant swelling.
▶️What to do when you have a swollen and hot knee?
⚫Elevate your leg: Keep your leg raised for 20–30-minute intervals throughout the day to help reduce swelling.
⚫Use ice: Cold therapy can help reduce swelling and pain but follow your physiotherapist’s guidance on its use.
⚫Stay active: Gentle walking can help reduce swelling. However, avoid unnecessary standing. Continue doing the prescribed exercises even if your knee is swollen.
⚫Stay hydrated and eat well: Proper hydration and a balanced diet support tissue healing and can help reduce swelling.
⚫Use compression: Compression stockings or an elastic bandage can help manage swelling. Your doctor or physiotherapist will advise on the best option for you.
⚫Rest: Get plenty of rest but also make sure to move the joint as instructed by your healthcare team.
▶️When to consult a doctor or physiotherapist?
You should seek immediate medical attention if you have a swollen, painful, hot knee because these symptoms can indicate serious conditions requiring prompt diagnosis and treatment
If you experience any of the following along with knee symptoms:
⚫ Fever or Chills: This could indicate a serious infection within the joint (septic arthritis)
⚫Inability to bear weight: If you cannot stand or walk on the affected leg at all.
⚫Numbness or tingling: This may suggest nerve involvement or compromised blood flow.
⚫Rapid swelling: Swelling that occurs within minutes or hours of an injury.
⚫Significant deformity: The knee joint looks visibly out of place.
These symptoms, particularly the combination of a hot, swollen, painful joint with systemic symptoms like fever, are red flags for serious medical issues such as:
❌septic arthritis.
❌A blood clot (deep vein thrombosis – DVT).
❌ Acute gout/pseudogout flares.
All these needs urgent medical management
Seeking advice from a healthcare professional who is accustomed to seeing these types of problems daily can lead to a more accurate diagnosis. Always see your doctor when you have knee swelling concerns.
Another approach to this situation is to trust the first opinion you received. This is personally the option that I choose most often.
▶️List of possible treatments for swollen hot knee
There are countless treatments or home remedies suggested for fighting knee swelling. Some are evaluated in clinical studies on healthy or sick adults, while others are not.
However, regardless of the cause of the swelling, the methods used to treat it remain the same.
Here is an overview of these treatments often suggested by professionals.
🟡Wearing compression stockings.
🟡Manual lymphatic drainage or massage.
🟡Using shock waves
🟡Wearing splint/braces
🟡Avoid prolonged standing or sitting.
🟡Perform an infiltrate puncture.
🟡Applying essential oils or ointment
🟡Reduce salt intake
🟡A diet rich in natural anti-inflammatories and antioxidants
🟡 Apply cold cryotherapy
🟡Surgical procedure
The list is incomplete but how do you choose from this list, do you try them all or not.
You can decide by looking at these criteria:
➡️Maximum effectiveness
➡️Minimum side effects
➡️Minimum cost
➡️Minimum dependence on a second person or equipment.
| I have seen people who have tried these 5 methods and of course scientific studies are in favour of them. ➡️Seek medical opinion to refine the cause and find a diagnosis. ➡️Wear compression stockings if you have no contraindications and they are well tolerated. ➡️Try to elevate the foot whenever you can ➡️Try walking regularly throughout the day. ➡️Avoid standing for long periods. |
▶️Recommendations from rheumatologists and surgeons
You might be surprised by these recommendations, perhaps you’ve been advised to follow a different treatment.
I have seen different professionals recommend it.
➡️Rheumatologists
A rheumatologist’s role involves diagnosing the underlying cause of the swelling and managing the condition to prevent permanent joint damage.
Normally a rheumatologist is consulted in the following situations.
❌Persistent Symptoms:
❌Inflammatory Symptoms:
❌Morning Stiffness:
❌Symmetrical Involvement
❌Systemic Symptoms:
❌No Obvious Injury
The Rheumatologist’s Approach for a swollen knee
⚪If there is significant fluid (effusion), the doctor may remove a sample of joint fluid to test for infection, gout crystals, or blood, which provides a definitive diagnosis in many cases.
⚪Prescribed medication or injection.
The surgeons’ approach for a swollen knee
Surgeons view a swollen knee as a sign that requires immediate evaluation, especially if the swelling is rapid, as it could indicate a fracture, ligament tear (like an ACL), or bleeding into the joint.
Surgical interventions for a swollen knee
⚪Knee arthroscopy
⚪Total knee replacement
Using osteopaths these are healthcare professionals who uses manual therapy, such as
⚪Massage.
⚪ Stretching, and manipulation of the joints and muscles, to diagnose, treat, and prevent health problems
➡️Physiotherapists approach for a swollen knee
Physiotherapy can help with a swollen knee by first conducting a thorough assessment to identify the cause and then creating a personalized rehabilitation plan for you.
⚪Initial treatment may involve pain management techniques like ice therapy, rest, and compression, as well as exercises to restore range of motion.
What do they have in common? Each healthcare professional will recommend something they themselves practice.
Rheumatologists, physiotherapists, and knee surgery, though different approaches, share core treatment goals for a swollen knee
They all aim at:
⚪Reducing pain and swelling
⚪Improve function and mobility.
⚪Muscle strengthening.
⚪Enhanced quality of life
⚪Patient education and self-management.
And they all recommend the same treatments as we have discussed above.
▶️What is better for a swollen knee: ice or heat?
Patients I see with newly swollen knees after an injury are normally advised to apply cold ice for 15 to 20 minutes every few hours to help reduce pain and swelling especially if the injury occurred in the last 48 hours.
After the initial swelling subsides usually after 24 to 48 hours, they are advised to switch to a heating pad to help relax the muscles and increase blood flow for stiffness.
Do not use heat on a fresh injury with swelling, as it can increase blood flow and worsen the swelling. Caution always wraps the ice pack or hot pad in a barrier like a towel to protect your skin.
▶️Is a hot tub good for swollen knees?
There is no empirical data about this. I don’t think we can expect a truly significant effect from a hot tub. And it can be complicated to implement
However I have seen people with swollen knees state that a hot tub helps them with swelling.
A hot tub is not recommended for a swollen knee, especially if the swelling is from a recent injury, because heat can increase blood flow and worsen swelling.
It is better to use ice for acute swelling, but a hot tub can be beneficial for chronic conditions like arthritis once the initial swelling has subsided.
From a theoretical perspective, a hot tub may help alleviate swelling in a knee.
Once inflammation decreases, buoyancy and warmth can help improve mobility, reduce pain and stiffness, and allow for gentle exercises.
We have come to the end of this article; any questions let’s meet in the comments section.
Wishing you a quick recovery!🙋
📚Sources:
Han J, Dyball S, Boon-Itt A, Taylor M. An acutely painful hot swollen knee. BMJ. 2022 Oct 27;379:e070231. doi: 10.1136/bmj-2022-070231. PMID: 36302515.
Reed MJ, Carachi A. Management of the nontraumatic hot swollen joint. Eur J Emerg Med. 2012 Apr;19(2):103-7. doi: 10.1097/MEJ.0b013e328348d8f8. PMID: 21730866.
Reed MJ, Carachi A. Management of the nontraumatic hot swollen joint. Eur J Emerg Med. 2012 Apr;19(2):103-7. doi: 10.1097/MEJ.0b013e328348d8f8. PMID: 21730866.
Lotz B, Palmer A, Deo SD. Beware of the hot swollen calf following knee replacement surgery: it might not be a deep vein thrombosis. BMJ Case Rep. 2019 Nov 21;12(11):e227830. doi: 10.1136/bcr-2018-227830. PMID: 31753818; PMCID: PMC6887406.
Moran E, Masters S, Berendt AR, McLardy-Smith P, Byren I, Atkins BL. Guiding empirical antibiotic therapy in orthopaedics: The microbiology of prosthetic joint infection managed by debridement, irrigation and prosthesis retention. J Infect. 2007 Jul;55(1):1-7. doi: 10.1016/j.jinf.2007.01.007. Epub 2007 Mar 6. PMID: 17343916.
Rafailidis PI, Kapaskelis A, Falagas ME. Knee septic arthritis due to Streptococcus pyogenes associated with acute thrombosis of the tibial and peroneal veins: case report and review of the literature. Scand J Infect Dis. 2007;39(4):368-70. doi: 10.1080/00365540600978963. PMID: 17454906.