Read below about swollen knee, including causes, treatment options and remedies. Or get a personalized analysis of your swollen knee from our A.I. health assistant. At Buoy, we build tools that help you know what’s wrong right now and how to get the right care.

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Swollen Knee Symptoms

You've been training for the marathon for months. You're loving how healthy and fit you feel but as the big day approaches your knee begins to give you some trouble. Before you know it, your swollen knee is making it difficult to walk, yet alone run.

Is there any way you'll be able to compete in the marathon?

Depending on the cause of your swollen knee, there's a good chance you can still cross the finish line.

If your knee is visibly swollen, there are a few other swollen knee symptoms you might notice such as:

  • Swelling, especially around your kneecap
  • Inability to bend or straighten the affected leg
  • Pain when putting weight on the affected leg

Are you at risk for swollen knee symptoms? Effusions are commonly referred to as fluid on the knee and can strike anyone but is more common in those who are active in sports, overweight, or the elderly.

In most cases, a swollen knee will resolve with time and rest. But there are complications that can arise. An excess of fluid that is not removed can cause weakened thigh muscles and permanent joint damage.

Swollen Knee Causes Overview

As soon as you notice a swollen knee, begin backtracking to see if you can discover the cause. Here are some of the most common to consider.


  • Trauma: A torn ligament [1] or cartilage [2] are some of the most common causes of a swollen knee. These injuries are typically experienced by athletes. [1]
  • Overuse: Walking or running more than usual can lead to inflammation and discomfort. [2]


  • Bursal infection: A cut near the kneecap that becomes infected can cause septic bursitis of the knee, with swelling as a symptom. Antibiotics can help if the condition is caught early. [3]
  • Surgical infection: Infections that develop after knee surgery should be acted upon quickly. Antibiotics can help, but in more serious infections, such as those after knee replacement surgery, additional surgeries could be required. [4]

Conditions and diseases:

  • Gout: Gout is caused by elevated levels of uric acid in the blood. Crystals form in the joints, leading to discomfort. Changes in diet and lifestyle can lower the likelihood of gout attacks. [1,5]
  • Rheumatoid arthritis: An autoimmune disease, those that suffer from RA experience attacks from their own body on healthy joints. [6]
  • Tumors: Though rare, a swollen knee can lead to the discovery of a tumor near the joint. [7] If you're experiencing fatigue and unexplained weight loss along with knee swelling, see your doctor. [7]

A.I. Health Assistant Causes for Swollen Knee

The list below shows results from the use of our A.I. Health Assistant by Buoy users who experienced swollen knee. This list does not constitute medical advice.

  1. 1.Infrapatellar Bursitis

    Bursae are small fluid-filled sacks located around the body in strategic locations to provide a cushion and help reduce friction. There is a pair of bursae below each kneecap (patella). Infrapatellar bursitis is a condition where these bursae are inflamed. It is a common cause of knee pain in people whose work involves frequent kneeling on hard surfaces.

    Condition goes away on its own in a few weeks.

    Top Symptoms:
    pain in one knee, spontaneous knee pain, dull, achy knee pain, knee pain that gets worse when going up stairs, knee pain that gets worse when squatting
  2. 2.Meniscal Injury

    A torn meniscus is one of the most common knee injuries. Any activity that causes forceful twisting of the knee, especially when putting the pressure of one's full weight on it, can lead to a torn meniscus.

    6 to 8 weeks

    Top Symptoms:
    pain in one knee, knee stiffness, knee instability, pain in the inside of the knee, swollen knee
    Primary care doctor
  3. 3.Acl Injury

    The ACL (anterior cruciate ligament) is a super-important tendon that connects the femur (thigh bone) to the tibia (shin), keeping the tibia from flying forward every time a step is taken. Tearing happens in a lot of accidents and sports, unfortunately.

    Full recovery may take months of physical therapy.

    Top Symptoms:
    knee pain, pain in one knee, knee instability, swollen knee, knee pain from an injury
    Symptoms that always occur with acl injury:
    knee pain
    Symptoms that never occur with acl injury:
    mild knee pain
    Hospital emergency room
  4. 4.Knee Arthritis

    Arthritis is inflammation of one or more of the joints. Pain, swelling, and stiffness are the primary symptoms of arthritis. Any joint in the body may be affected by the disease, but it is particularly common in the knee.

    Knee arthritis is a chronic problem once it develops.

    Top Symptoms:
    pain in both knees, knee stiffness, knee instability, swollen knee, morning joint stiffness
    Symptoms that always occur with knee arthritis:
    pain in both knees
    Primary care doctor
  5. 5.Baker's Cyst (Popliteal Cyst)

    A Baker's cyst, also called as Popliteal cyst, is a fluid-filled mass that causes a bulge and a feeling of tightness behind the knee. The pain can get worse when the knee is fully flexed or extended.

    Recovery with nonsurgical treatment varies

    Top Symptoms:
    calf pain, swollen knee, knee pain that gets worse when squatting, knee instability, dull, achy knee pain
    Symptoms that always occur with baker's cyst (popliteal cyst):
    lump on the back of the knee, constant knee lump
    Primary care doctor

    Swollen Knee Checker

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  6. 6.Lyme Disease

    Lyme Disease is a bacterial infection caused by the bite of a tick, which needs to latch on for a few days to transmit the bacteria. This infection can affect the skin, but more dangerously, the nervous system.

    If treated properly, people are typically cured but may have symptoms for a few months even without signs of an actual infection.

    Ultra rare
    Top Symptoms:
    fatigue, headache, irritability, muscle aches, loss of appetite
    Primary care doctor
  7. 7.Rheumatoid Arthritis

    Rheumatoid arthritis (RA) is a form of arthritis that causes pain, swelling, stiffness and loss of function in your joints. It can affect any joint but is common in the wrist and fingers. RA is an autoimmune disorder, meaning that it is caused by the immune system incorrectly attacking the joints when it shouldn't.

    RA is a chronic disease which requires lifelong control.

    Top Symptoms:
    fatigue, depressed mood, joint pain, muscle aches, daytime sleepiness
    Primary care doctor
  8. 8.Osteochondritis Dissecans

    At joints where bones meet, bones are covered with a layer of cartilage which provides shock absorbance and lubrication. Osteochondritis dissecans is a condition where a piece of cartilage with a thin layer of bone detach from the larger bone, causing pain.

    Conservative treatment should resolve the problem in 3-6 months.

    Top Symptoms:
    pain in one knee, knee stiffness, knee instability, knee pain that gets worse during a run, pop in the knee
    Primary care doctor
  9. 9.Psoriatic Arthritis

    Psoriasis is a skin disease that causes itchy or sore patches of thick, red skin with silvery scales. Some people who have psoriasis also get a form of arthritis (inflammation and swelling of joints) called psoriatic arthritis.

    This type of arthritis can be managed with treatment, and permanent damage can be prevented. However, the underlying cause (psoriasis) is currently incurable.

    Top Symptoms:
    shoulder pain, lower back pain, joint pain, upper back pain, hip pain
    Primary care doctor
  10. 10.Deep Vein Thrombosis

    Deep vein thrombosis (DVT) is a blood clot that forms in a vein deep in the body. Most deep vein clots occur in the lower leg or thigh.

    Curable with medication or surgery but may recur.

    Top Symptoms:
    fever, thigh pain, upper leg swelling, calf pain, butt pain
    Hospital emergency room

Swollen Knee Treatments and Relief

A swollen knee rarely requires a trip to the emergency room. Unless you are experiencing severe bleeding or a visible injury, you can treat your symptoms at home. [2]

However, make an appointment with a doctor if you are experiencing:

  • Pain that continues to worsen in severity. [2]
  • Pain that isn't alleviated through medication or home care. [2]
  • Your knee becomes red and feels warm to the touch. [2]

Ignoring a swollen knee can be impossible.

To lessen the pain and encourage healing, consider the following swollen knee treatments:

  • R.I.C.E. Formula: This acronym is the first treatment approach you should take. Rest the knee whenever possible. Ice it for 20 minutes several times a day. Compress the affected joint to limit swelling and Elevate the leg whenever possible. [9]
  • OTC pain relievers: To ease pain, try over-the-counter medication such as NSAIDs (ibuprofen or acetaminophen) for temporary relief. You should still rest the knee. [9]
  • Fluid removal: If you're not noticing any lessening of pain or any change in your knee's appearance after several days, having a doctor remove excess fluid can provide pain relief. However, unless the cause of the buildup is known, this treatment may not prevent more fluid from collecting. [9]

A swollen knee can slow you down, but it doesn't need to stop life in its tracks. Find the cause of your pain, either on your own or with the help of a doctor, and then make treatment your utmost priority. You'll be back to normal, and crossing those finish lines, in no time. [9]

FAQs About Swollen Knee

Here are some frequently asked questions about swollen knee.

Why is my knee swollen after a fall?

A swollen knee occurs after a fall because the fall has caused some degree of damage to the tissue of the joint or the tissue around the joint. The trauma has injured the knee and the body then causes fluid to accumulate as cells rush in to clean up and repair the damage. [10]

What is better for knee pain: heat or cold?

Heat and cold are both useful. Heat allows dilation of blood vessels, which can help reduce some of the swelling in the knee, and can relax the muscles and tendons to allow healing to occur. [9] Relaxing tense muscles can help decrease pain from muscle sprains. [11] Cold is a quick way to numb the joint and reduce swelling in the short term. [10]

How can you reduce fluid on the knee?

This depends on the cause of fluid. If the swelling is from an injury, the best way to reduce the swelling is to rest the knee and stop using it, elevate it to reduce blood flow to it, keep the swelling from getting worse by placing ice on it to control pain, and compress it to control the swelling. [10] If the swelling is from an infection, it will need to be drained immediately with a needle and treated with antibiotics (usually intravenously). [4,7]

How long should swelling last after knee surgery?

Swelling can last up to six weeks after surgery, but is usually significantly decreased within three to four weeks. It depends on the cause of the surgery and the medical conditions of the patient. Surgeries where an infection is possible or is being treated may result in swelling for longer periods of time. Older individuals may also have inflammation for longer periods of time. [4,7,12]

Why do my knees swell when I run?

The repeated trauma of running, especially on concrete or asphalt, can cause knee swelling. This can be prevented by running on softer surfaces like astroturf, grass, dirt, sand, or clay. It may also be prevented by wearing proper footwear that provides enough support to your feet if you are going to run on a hard surface. [13]

Questions Your Doctor May Ask About Swollen Knee

  • Q.Do you feel like your knee is unstable, weak, or giving out?
  • Q.Do you feel like your knee is locking from time to time?
  • Q.Do you often feel your knees buckling?
  • Q.Did you feel your knee cap pop out of place?

If you've answered yes to one or more of these questions, try our swollen knee symptom checker to find out more.

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Swollen Knee Symptom Checker Statistics

  • People who have experienced swollen knee have also experienced:

    • 13% Knee Pain
    • 4% Moderate Knee Pain
    • 4% Pain in One Knee
  • People who have experienced swollen knee had symptoms persist for:

    • 30% Less Than a Week
    • 30% Over a Month
    • 18% Less Than a Day
  • People who have experienced swollen knee were most often matched with:

    • 54% Acl Injury
    • 36% Meniscal Injury
    • 9% Infrapatellar Bursitis
  • Source: Aggregated and anonymized results from visits to the Buoy AI health assistant (check it out by clicking on “Take Quiz”).

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  1. Gupte C, St Mart JP. The acute swollen knee: Diagnosis and management. J R Soc Med. 2013;106(7):259-268. NCBI Link.
  2. Swollen knee. NCH Healthcare System. Updated May 21, 2015. NCHMD Link.
  3. Blahd WH Jr, Husney A, Russo ET, eds. Septic bursitis. University of Michigan: Michigan Medicine. Updated July 30, 2018. UofM Health Link.
  4. Foran JRH, Peace WJ. Joint replacement infection. American Academy of Orthopaedic Surgeons: OrthoInfo. Updated January 2018. OrthoInfo Link.
  5. Gout. Wake Forest Baptist Health. Wake Health Link.
  6. Husney A, Poinier AC, Gabica MJ, Romito K, Shadick NA, eds. Rheumatoid arthritis. University of Michigan: Michigan Medicine. Updated June 10, 2018. UofM Health Link.
  7. Johnson MW. Acute knee effusions: A systematic approach to diagnosis. American Family Physician. 2000;61(8):2391-2400. AAFP Link.
  8. Leopold SS. Osteoarthritis of the knee. UW Medicine: Orthopaedics and Sports Medicine. Updated February 14, 2011. UW Medicine Link.
  9. Medical therapies for knee sprains, strains & tears. NYU Langone Health. NYU Langone Health Link.
  10. Swelling: The body's reaction to injury. Nationwide Children’s Hospital. Nationwide Children’s Hospital Link.
  11. Using heat and cold for pain relief. Arthritis Foundation. Arthritis Foundation Link.
  12. What your incision should look like after total knee replacement. Allina Health. Updated May 26, 2017. Allina Health Link.
  13. Knee pain and other running injuries. NHS. Updated June 20, 2018. NHS Link.