A swollen knee can be caused by direct trauma or falls during sports, both which can cause ligament injuries and lead to swollen. Inflammation may also occur with some illnesses, like arthrosis, arthritis, infections or cysts.

Generally, swelling in the knee occurs due to increase synovial fluid in the area, which is a fluid need to keep the joint lubricated.

It is important to consult an orthopedic surgeon for assessment and treatment as necessary. Swelling can be treated with rest, cold compresses and anti-inflammatories.

What causes knee swelling?

A swollen knee can occur due to:

1. Direct trauma

After following or direct trauma to the knee (like a blow or car accident), the knee can become very swollen and painful. These are usually signs of a sprain or contusion, which can occur when the synovial lining (which covers the joint) becomes swollen.

This can occur after a fall and can lead to swelling over night. Swelling can also occur due to accumulation of blood within the knee, leaving the outer knee purple and bruised.

What to do: Place a cold compress on the knee to relieve pain. Be sure to rest with the knee elevated, and to apply anti-inflammatory topicals over the affected areas.

2. Arthrosis

Arthrosis can give the knee a swollen appearance from deformities and abnormal bone growth. It makes the knee appear larger and leave it less flexible. This finding is common in older adults, but it can also affect younger adults over 40 years of age.

What to do: Physiotherapy is advised to relieve pain, with methods like electronic appliance, joint manipulation, stretching and strengthening recommended. Other important measures include lifestyle changes, like weight loss, avoiding strenuous activity, and opting for supportive shoes may also be beneficial.

3. Arthritis

Knee arthritis can be triggered by a fall, excessive weight, normal aging or auto-immune diseases (like rheumatoid arthritis). Reactive arthritis is also possible, which is knee pain and swelling from other illnesses, like gonorrhea and intestinal parasites.

What to do: You should see your doctor for assessment of symptoms, especially if you have other chronic diseases or are treating another condition. With arthritis, the doctor may prescribe anti-inflammatory medication and physiotherapy. Lifestyle changes are also recommended, and heavy physical activity should be avoided. An anti-inflammatory diet is advised with low intake of processed foods, like sausage and bacon.

4. Knee infection

Knees that present with redness and swelling may be a sign of an infectious or inflammatory process.

What to do: You should see your doctor for assessment, espeically if the knee is very warm to the touch, if swelling persists for over 7 days, if you have difficulty moving the leg, or if you have other symptoms of infection, like a fever.

5. Baker’s cyst

A baker’s cyst is a small lump that can be felt at the back of the knee. These can leave the knee slightly swollen, and patients often report pain and rigidity that worsens with movement and physical activity,

What to do: Physio is recommended to manage pain and discomfort, however it will not eliminate the cyst. Larger and symptomatic cysts may require injection therapy and removal.

6. Ligament rupture

A ruptured ligament usually occurs due to abrupt knee movements, from playing soccer for example. It is possible to hear a strong crack at the moment of rupture, which can help with diagnosis. Mild injuries, like a ligament strain, can cause knee clicking and swelling as well.

What to do: You should see an orthopedic surgeon for imaging to determine the severity of rupture. The doctor will evaluate the need for treatment which can range from physiotherapy to surgery.

7. Meniscus injury

A meniscus injury may not always cause knee swelling, but many patients will present with mild swelling on the side of the knee. Other common symptoms include pain with walking and when going up or down stairs.

What to do: You are advised to see an orthopedic surgeon for imaging tests like an MRI to confirm a diagnosis. Treatment usually involves physiotherapy, however more severe cases may require surgical repair.

8. Patella fracture

A fall or abrupt accident can dislocate the patella or fracture it. In addition to pain and swelling, the patellar bone may be displaced out of its usually location.

What to do: Proceed immediately to the emergency room for X-ray and assessment. The doctor may reposition a dislocated patella manually, however surgery may be necessary. You can apply a cold compress to relieve pain and swelling until you are assessed. Anti-inflammatories may also help with pain, however if pain persists for over 3 weeks, physio may be needed.

9. Bursitis

Knee bursitis is the inflammation of the small fluid-filled bursa sac within the knee. A bursa helps to decrease friction and stress on the pressure points between the bones, tendons, muscles and skin.

Knee bursitis can cause pain and limit mobility. inflammation usually occurs due to overloading of the knee, a strong blow or as a result of other health complication, like arthrosis, arthritis or gout.

What to do: Treatment will usually depend on the underlying cause of bursitis. Symptoms can be relieved with rest, ice and elevation, as well as anti-inflammatory medications, like diclofenac and ibuprofen. Infectious bursitis may require antibiotic treamtent.

10. Pregnancy

Having swollen knees during pregnancy is a normal finding. It occurs due to natural swelling caused by increased estrogen and progesterone levels, which cause vasodilation. Increased belly size and overall weight gain from pregnancy can also lead to increased fluid accumulation and inflammation in the knee tissues.

What to do: Rest with your legs elevated when possible and use comfortable shoes to both prevent and manage swollen knees. Speak to your OB before using any medications to treat swelling and pain.

How to treat at home

You can use the following methods to manage mild knee swelling and pain at home:

Adequate rest, ensuring your legs are elevated as high as comfortably possible
Apply a cold compress within the first 48 hours of an injury to reduce swelling
Apply a warm compress after the first 48 hours to relieve muscular pain
Take anti-inflammatory and analgesic medication, like acetaminophen and ibuprofen, as directed by your doctor

If pain and swelling persist for over 7 days, you should see an orthopedic surgeon to determine a cause for the inflammation and to start treatment. The doctor may recommend physiotherapy, or, in more serious cases, aspirate accumulated fluid with a needle or recommend surgery.