Symptoms A-Z

Swollen Knees Symptoms & 10 Reasons Your Knees Are Swollen

Understand your swollen knees symptoms, including 8 causes & treatment options for your swollen knees.

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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."

Common characteristics of swollen knees

Swollen knees can likely be described by the following details:

  • Onset: Swelling that may appear suddenly or gradually
  • Swelling may appear with or without an injury
  • Intensity of pain: This 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

The duration of symptoms is ultimately dependent on the cause.

  • Temporary: Swelling that occurs a day or two after an injury is usually minor and will heal on its own.
  • Chronic: Gradual swelling that occurs when there has been no injury indicates an inflammatory, autoimmune, or degenerative condition.
  • Sudden and severe: 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 50 are more likely to be affected, although anyone can experience swollen knees. Athletes in heavy training are also particularly susceptible.

When are swollen knees symptoms most likely to occur?

Swollen knees are more likely to occur after:

  • Injury
  • A period of overtraining or overuse
  • Contracting certain forms of arthritis

Are swollen knees serious?

The severity of swollen knees is ultimately dependent on the cause.

  • Not serious: Mild bilateral knee swelling after a long period of work or exercise is usually not serious.
  • Moderately 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.
  • Serious: 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

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 [4].

  • Autoimmune disorders: These 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: These 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: This will cause rapid swelling with redness, pain, and fever.
  • A bacterial infection elsewhere in the body: A sexually transmitted disease can sometimes set up an immune response throughout the body with severe swelling and pain in the joints.
  • Lyme disease: This can cause swollen joints as a late-stage symptom [5].

Degenerative disease

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

Traumatic causes

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.

  • Overuse/overtraining: Usually from sports such as rowing, distance running, or weightlifting
  • Acute injury: This can occur from automobile accidents, sports or work injuries resulting in being struck across both knees, and falls.

Tumors and cysts

Although less common, the following can result in swollen knees.

  • 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: These are very rare around the knee.

8 Possible Swollen Knees Conditions

The list below shows results from the use of our quiz by Buoy users who experienced swollen knees. This list does not constitute medical advice and may not accurately represent what you have.

Prepatellar bursitis

Prepatellar bursitis is an inflammation of a fluid-filled sac (bursa) located in front of the knee (prepatellar) that normally acts as a cushion to help reduce friction. It can be caused by prolonged kneeling, such as for work, or due to injury or infection, and can either be ...

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

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

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.

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

Swollen Knees Symptom Checker

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Psoriatic arthritis

Psoriatic arthritis is a condition which causes inflammation of the joints. In most circumstances, psoriatic arthritis presents between the ages of 30 and 50 years and occurs after the manifestation of the symptoms of psoriasis, which is a disease of the skin. Psoriatic arthritis...

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

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

Rheumatoid arthritis

Arthritis is a general term for multiple conditions that cause painful inflammation and stiffness throughout the body. Rheumatoid arthritis (RA) is a chronic condition that is autoimmune in nature, meaning that the body's immune system which normally protects the body by att...

Swollen Knees Treatments and Relief

When swollen knees are an emergency

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.

When to see a doctor for swollen knees

You should schedule an appointment for:

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

At-home remedies for swollen knees

Remedies you can try at home include the following.

  • Rest: Try keeping the knee elevated as well if 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: Make sure it is not overly tight and does not increase your pain.
  • Pain relievers: Take over-the-counter pain relievers such as ibuprofen (Advil, Motrin) or other NSAIDs.

Questions Your Doctor May Ask About Swollen Knees

To diagnose this condition, your doctor would likely ask the following questions:

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

The above questions are also covered by our A.I. Health Assistant.

If you've answered yes to one or more of these questions

Take a quiz to find out what might be causing your swollen knees

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 were most often matched with:

  • 50% Meniscal Injury
  • 37% Prepatellar Bursitis
  • 12% Infrapatellar Bursitis

People who have experienced swollen knees had symptoms persist for:

  • 30% Less than a week
  • 30% Over a month
  • 18% Less than a day

Source: Aggregated and anonymized results from visits to the Buoy AI health assistant (check it out by clicking on “Take Quiz”).

Swollen Knees Symptom Checker

Take a quiz to find out what might be causing your swollen knees

References

  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. Ma CB. Knee pain. U.S. National Library of Medicine: MedlinePlus. Updated December 6, 2018. MedlinePlus Link
  3. Johnson MW. Acute knee effusions: A systematic approach to diagnosis. American Family Physician. 2000;61(8):2391-2400. AAFP Link
  4. Synovitis. HSS. HSS Link
  5. Smith BG, Cruz AI, Milewski MD, Shapiro ED. Lyme disease and the orthopaedic implications of lyme arthritis. J Am Acad Orthop Surg. 2011;19(2):91-100. NCBI Link

Disclaimer: The article does not replace an evaluation by a physician. Information on this page is provided as an information resource only, and is not to be used or relied on for any diagnostic or treatment purposes.