Read below about swollen knees, including causes, treatment options and remedies. Or get a personalized analysis of your swollen knees 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.

A.I. Health Assistant

Take a quiz to find out why you’re having swollen knees

Take Quiz

Swollen Knees Symptoms

The knees are very strong weight-bearing joints, but vulnerable to illness and injury. There are no muscles within the knee joints – only bones, cartilage, and tough ligaments, which have little flexibility. That means they are relatively easy to strain or tear if you're an athlete and you overtrain.

The knees are also filled with shock absorbers called bursa. These bursae, and the lining of the knee joint that provides them with fluid, are vulnerable to infection and to autoimmune conditions which can affect both knees at the same time. Swelling of the knee is sometimes called an effusion, or "water on the knee."


  • Swelling that may appear suddenly or gradually.
  • Swelling may appear with or without an injury.
  • Pain that may range from mild to moderate to severe, but worsens when you try to move the knee or bear weight on it.
  • Stiffness on trying to move.
  • Bruising, especially with trauma, although it may sometimes appear with illness-caused swelling.

Duration of symptoms:

  • Swelling that occurs a day or two after an injury is usually minor and will heal on its own.
  • Gradual swelling that occurs when there has been no injury indicates an inflammatory, autoimmune, or degenerative condition.
  • Rapid swelling with heat, redness, and pain indicates an infection and needs treatment right away.

Who is most often affected by swollen knees symptoms?

  • People past the age of about fifty, though anyone can be affected.
  • Athletes in heavy training.

When are swollen knees symptoms most likely to occur?

  • After an injury.
  • After a period of overtraining or overuse.
  • After contracting certain forms of arthritis.

Are swollen knees serious?

  • Mild bilateral knee swelling after a long period of work or exercise is usually not serious.
  • If the swelling is not properly treated and becomes chronic, it will almost certainly damage the underlying cartilage, bone, and joint structure of the knee.
  • If there is redness, pain, and fever along with the swelling, it's important to see a medical provider as soon as possible.

Swollen Knees Causes Overview

We've listed several different swollen knees causes here, in approximate order from most to least common:

Inflammation of the synovium.

  • The synovium is the lining of the knee joint and produces synovial fluid to keep the cartilage lubricated. If the joint is inflamed, synovial fluid may be overproduced and cause gradual swelling.
  • Autoimmune disorders may attack the synovium, resulting in inflammation and severe swelling of both knees along with redness and pain.
  • The inflammation may spread to the other cushioning structures within the knee joint and create pain and swelling.
  • Mineral deposits may form within the knee joint, causing intense pain with rapid swelling, warmth, and redness.

Infection of the synovium.

  • A bacterial infection of the synovium will cause rapid swelling with redness, pain, and fever.
  • A bacterial infection elsewhere in the body, such as a sexually transmitted disease, can sometimes set up an immune response throughout the body with severe swelling and pain in the joints.
  • Lyme disease can cause swollen joints as a late-stage symptom.

Degenerative disease of the cartilage. Pain and swelling result when the cartilage, and sometimes the bone, begins to wear away.


  • Overuse/overtraining: usually from sports such as rowing, distance running, or weightlifting.
  • Acute injury:

    • Automobile accident.
    • Sports or work injury resulting in being struck across both knees.
    • Falls
    • Any of these injuries can fracture bones, and the bursae, tendons, and cartilage will also be injured.
    • The swelling is caused by the damaged tissue bleeding into the knee following the injury.

Tumors and cysts:

  • Sometimes a benign, fluid-filled cyst can form at the back of knee and create swelling, mild pain, and stiffness. It is rare, but possible, for these cysts to appear on both knees at the same time.
  • Cancerous tumors are very rare around the knee.

A.I. Health Assistant Causes for Swollen Knees

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

  1. 1.Prepatellar Bursitis

    Prepatellar bursitis occurs when the bursa, a fluid-filled sac, around the knee becomes inflamed and painful.

    Recovery depends on extent of inflammation.

    Top Symptoms:
    pain in the front of the knee, swollen knee, knee redness
    Symptoms that always occur with prepatellar bursitis:
    pain in the front of the knee
    Primary care doctor
  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.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
  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

    Swollen Knees Checker

    Take a quiz to find out why you’re having swollen knees.

    Take Quiz
  5. 5.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
  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.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
  8. 8.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

Swollen Knees Treatments and Relief

Seek immediate treatment in the emergency room or call 911 if you have:

  • Sudden, rapid swelling within one or both knees that appears within a few minutes to a couple of hours, along with redness, pain, stiffness, and heat in the knee. You may also feel ill and feverish. These are all signs of infection, which can spread quickly.

Schedule an appointment for:

  • Chronic swelling that does not subside, especially if you also feel ill.
  • A referral for physical therapy to help strengthen injured knees.

Remedies that you can try at home:

  • Rest and keeping the knee elevated if at all possible.
  • Ice or cold packs to help reduce swelling. Avoid heat with a swollen knee in case it is caused by an infection, because heat can cause the pus within the joint to spread.
  • Use a compression wrap, as long as it is not overly tight and does not increase your pain.
  • Take over-the-counter pain relievers such as ibuprofen or other NSAIDs.

Questions Your Doctor May Ask About Swollen Knees

  • Q.Do you often feel your knees buckling?
  • Q.At work,, do you often have to kneel on hard surfaces for extended amounts of time?
  • Q.What is your body mass?
  • Q.Do you feel like your knee is unstable, weak, or giving out?

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

Take Quiz

Swollen Knees Symptom Checker Statistics

  • People who have experienced swollen knees have also experienced:

    • 8% Knee Pain
    • 3% Pain in Both Knees
    • 3% Moderate Knee Pain
  • People who have experienced swollen knees had symptoms persist for:

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

    • 50% Meniscal Injury
    • 37% Prepatellar Bursitis
    • 12% Infrapatellar Bursitis
  • Source: Aggregated and anonymized results from visits to the Buoy AI health assistant (check it out by clicking on “Take Quiz”).

A.I. Health Assistant

Take a quiz to find out why you’re having swollen knees

Take Quiz