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Swollen Knee: Causes and Treatment Options

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Last updated March 30, 2024

Swollen knee quiz

Take a quiz to find out what's causing your swollen knee.

A swollen knee is mainly a sign of excess fluid in the knee. Learn about common causes of knee swelling symptoms; including bursitis, gout, arthritis and overuse.

Swollen knee quiz

Take a quiz to find out what's causing your swollen knee.

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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.

Common accompanying symptoms of a swollen knee

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 are more common in those who are active in sports, overweight, or 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.

Causes of a swollen knee

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.


Injuries to the knee will likely result in swelling.

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

Infectious causes

Infections of the knee will result in swelling.

  • 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.
  • 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.

Conditions and diseases

Certain conditions affecting the knee will result in swelling.

  • 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.
  • Rheumatoid arthritis: An autoimmune disease, those that suffer from RA experience attacks from their own body on healthy joints.
  • Tumors: Though rare, a swollen knee can lead to the discovery of a tumor near the joint. If you're experiencing fatigue and unexplained weight loss along with knee swelling, see your doctor.

This list does not constitute medical advice and may not accurately represent what you have.

Rheumatoid arthritis

Rheumatoid arthritis is a chronic inflammatory disorder that affects the lining of the joints, causing them to become thickened and painful. It can also affect other parts of the body such as the heart, lungs, eyes, and circulatory system.

Rheumatoid arthritis is an autoimmune disease, which means the body's immune system turns against itself for unknown reasons.

Most at risk are women from ages 30-60. Other risk factors are family history, smoking, and obesity.

Early symptom include warm, swollen, stiff, painful joints, especially the fingers and toes; fatigue; and fever. Usually, the same joints on both sides of the body are affected.

If untreated, irreversible joint damage and deformity can occur, with other complications. Early diagnosis can allow preventive treatment to begin as soon as possible.

Diagnosis is made through physical examination; blood tests; and x-ray, CT scan, or MRI.

There is no cure for rheumatoid arthritis, but the disease can be managed to improve quality of life. Treatment includes nonsteroidal anti-inflammatory drugs; steroids; anti-rheumatic drugs; physical therapy; and sometimes surgery to repair the joints.

Psoriatic arthritis

Psoriatic arthritis is a complication of psoriasis, which causes the skin to become thickened, red, and scaly. Arthritis may appear before or after the psoriasis appears.

Both conditions are autoimmune diseases, where the body attacks itself, and are thought to be caused by genetic and environmental factors.

Most susceptible are people from 30 to 50 years of age with a family history of the disease and who already have psoriasis.

Symptoms include the joints on one or both sides of the body becoming painful, swollen, and hot; swelling and deformity of the fingers and toes; pitted, flaking fingernails; foot pain in the heels and soles; and joint pain in the low back pain.

It is important to seek treatment, as psoriatic arthritis can permanently damage the joints, eyes, and heart.

Diagnosis is made through physical examination, x-rays, and MRI. Blood tests and joint fluid tests can confirm psoriatic arthritis.

Treatment includes over-the-counter, nonsteroidal anti-inflammatory drugs; anti-rheumatic medication; immunosuppressants; and steroid injections for the joints. Surgery to replace damaged joints may also be tried.

Osteochondritis dissecans

Osteochondritis dissecans, also called OCD, is a joint condition. It occurs when there is not enough blood flow within the end of a bone, under the protective cartilage. These bone layers begin to die and separate from the main bone, taking the cartilage with them.

The exact cause is not known. It may be due to overtraining a young person before the bone is entirely mature, which can interfere with blood supply.

Most susceptible are children and teenagers. The condition is found most often in only one joint, usually the ankle, knee, or elbow. However, any joint can be affected and there may be more than one.

Symptoms include swelling and pain in the joint during exercise, and sometimes "locking" of the joint. Osteochondritis dissecans may lead to osteoarthritis if not treated.

Diagnosis is made through patient history, physical examination, and imaging.

Treatment first involves rest because in children who are still growing, the bone and cartilage may heal spontaneously. If there are loose pieces of bone within a joint, surgery may be necessary.

Rarity: Rare

Top Symptoms: pain in one knee, knee stiffness, knee instability, knee pain that gets worse during a run, pop in the knee

Urgency: Primary care doctor

Meniscal injury

The menisci are the two pieces of cartilage serving as shock absorbers in the knee, between the lower end of the thighbone and the top of the shinbone. A torn meniscus is commonly referred to as "torn cartilage" in the knee.

Damage to a meniscus often happens along with another injury to the knee, especially when there is any forceful, twisting movement or a direct hit such as a tackle.

Older people may tear a meniscus through normal activity if the cartilage has become thin and worn due to aging.

Symptoms include pain, stiffness, and swelling. The knee will simply not work correctly and may catch, lock up, or give way.

Diagnosis is made through patient history, physical examination, simple motion tests, and imaging such as x-ray or MRI.

Depending on the exact form of the injury, the tear may be allowed to heal on its own with supportive care such as rest, ice, and nonsteroidal anti-inflammatory pain medication. In other cases, arthroscopic surgery followed by rehabilitation may be needed.

Rarity: Common

Top Symptoms: pain in one knee, knee stiffness, knee instability, pain in the inside of the knee, swollen knee

Urgency: Primary care doctor

Lyme disease

Lyme disease is a bacterial illness transmitted through the bite of the deer tick (black-legged tick) after it has been attached for at least 36-48 hours. These may be tiny, immature ticks that are difficult to see, often attaching in a place on the body where hair grows.

The disease does not spread through casual contact, either between humans or between humans and pets.

Early symptoms include fever, chills, headache, and body aches. There may be a rash around the tick bite, which sometimes enlarges to form a clear circle around the bite.

Later symptoms are severe with headaches, neck stiffness, further rashes, facial drooping (palsy,) and joint pain and swelling. This is a medical emergency. Take the patient to the emergency room or call 9-1-1.

Untreated Lyme disease in a pregnant woman can lead to stillbirth, but antibiotics will usually prevent this.

Diagnosis is made through symptoms as well as a blood test.

Treatment consists of oral antibiotics in most cases, though severe cases may require IV antibiotics.

Rarity: Ultra rare

Top Symptoms: fatigue, headache, irritability, muscle aches, loss of appetite

Urgency: Primary care doctor

Knee arthritis

Knee arthritis means that there is inflammation and abnormal wear of one or both of the two joints in the knee.

Arthritis in any joint is most often be caused by long-term wear and tear, called osteoarthritis; by an autoimmune condition that attacks the joints, called rheumatoid arthritis; or by an injury, called post-traumatic arthritis.

Symptoms include pain, which becomes worse with use of the joint; limited range of motion, meaning the shoulder joint cannot move as far as it once did; and pain when resting or trying to sleep.

Knee arthritis cannot be cured, but symptoms can be managed to improve quality of life and ease pain and discomfort.

Diagnosis is made through patient history, physical examination, and x-rays. To confirm, an injection of anesthetic may be placed into the joint. If the pain is eased, arthritis is almost certainly the cause.

Treatment involves physical therapy; nonsteroidal anti-inflammatory drugs to ease discomfort and inflammation; and corticosteroid injections into the knee to relieve pain. Surgery and knee joint replacement can be done in some cases.

Rarity: Common

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

Urgency: Primary care doctor

Infrapatellar bursitis

Infrapatellar bursitis is an inflammation of the bursa, or small cushioning sacs, beneath the patella, or kneecap. The condition may affect either the superficial bursa or the deep bursa.

Superficial infrapatellar bursitis is found in those whose work requires them to kneel on hard surfaces, and so it is known as housemaid's knee, clergyman's knee, parson's knee, or vicar's knee.

Deep infrapatellar bursitis can occur from chronic overuse, as with sports training and other hard physical work.

Either form of the condition can also be caused by hemorrhage, infection, traumatic injury, or inflammatory diseases such as arthropathy. Some cases may be idiopathic, meaning they occur in a particular individual for no clear reason.

Symptoms include swelling of the knee and pain below the kneecap.

Diagnosis is made through patient history and physical examination as well as x-ray, CT scan, or MRI.

Treatment involves rest; heat; nonsteroidal anti-inflammatory drugs to reduce pain and swelling; a knee brace; and sometimes corticosteroid injections into the knee.

Rarity: Uncommon

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

Urgency: Self-treatment

Deep vein thrombosis

A deep vein thrombosis (DVT) occurs when a blood clot forms in a vein deep in the body, usually in the lower leg or thigh. DVT can cause swelling, pain, and redness in the affected leg. Some of the risk factors for developing DVT include obesity, pregnancy, cancer, surgery, and previous history of blood clots.

You should consider calling your primary care or urgent care provider. Deep vein thrombosis can be evaluated with a review of your symptoms, a physical exam, and an ultrasound. A blood test may also be performed. Once diagnosed, DVT can be treated with blood-thinning medication, which is usually taken for three months.

Rarity: Uncommon

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

Urgency: Hospital emergency room

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.

Although a Baker's cyst may cause swelling and make you uncomfortable, treating the probable underlying problem (i.e. knee arthritis) usually provides relief. Your doctor will be able to determine whether surgery, though unlikely, is needed.

Rarity: Uncommon

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

Urgency: Primary care doctor

Acl injury

The ACL (anterior cruciate ligament) is an important tendon that connects the femur (thigh bone) to the tibia (shin), stabilizing the knee. ACL injuries are commonly caused by sports-related injuries.

Your primary care provider or an urgent care provider can do an exam, and imaging can determine the extent of the injury. Treatment depends on the severity of the injury, ranging from rehabilitation to full surgery.

Rarity: Rare

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

Urgency: 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.

When to see a doctor for a swollen knee

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

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

At-home treatments for a swollen knee

Ignoring a swollen knee can be impossible. To lessen the pain and encourage healing, consider the following swollen knee treatments:

  • R.I.C.E. method: 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.
  • OTC pain relievers: To ease pain, try over-the-counter medication such as NSAIDs, such as ibuprofen (Advil, Motrin) or acetaminophen (Tylenol) for temporary relief. You should still rest the knee.
  • 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.

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.

FAQs 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.

What is better for knee pain, heat or cold?

Heat and cold are both useful. Heat allows dilation of blood vessels that can help reduce some of the swelling in a knee, and can relax the muscles and tendons allowing healing to occur. It can also serve as a way to relax tense muscles and decrease pain from muscle sprains. Cold is a quick way to numb the joint and reduce swelling in the short term.

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. If the swelling is from an infection, it will need to be drained immediately with a needle and treated with antibiotics (usually intravenously).

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.

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.

Questions your doctor may ask about swollen knee

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

Self-diagnose with our free Buoy Assistant if you answer yes on any of these questions.

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The stories shared below are not written by Buoy employees. Buoy does not endorse any of the information in these stories. Whenever you have questions or concerns about a medical condition, you should always contact your doctor or a healthcare provider.
Dr. Rothschild has been a faculty member at Brigham and Women’s Hospital where he is an Associate Professor of Medicine at Harvard Medical School. He currently practices as a hospitalist at Newton Wellesley Hospital. In 1978, Dr. Rothschild received his MD at the Medical College of Wisconsin and trained in internal medicine followed by a fellowship in critical care medicine. He also received an MP...
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