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By Dr Dulcy Rakumakoe

Chief Executive Officer

Everything you need to know about a swollen knee

Struggling with a swollen knee? Here's what could be causing it and when to see the doctor.

When excess fluid collects in or around your knee joint it causes a swollen joint. This can happen as a result of trauma, overuse injuries, or an underlying disease or condition. To find the cause of the swelling, your doctor can test a sample of the fluid for infection, disease or blood from an injury. Removing some of the fluid may help reduce the pain and stiffness. Once the underlying cause is known, treatment can then be started. You need to urgently visit your doctor if self-care measures, such as ice and rest, don’t improve symptoms. Seek immediate medical attention if one knee becomes red and is warm to the touch compared to the other knee. This can be a sign of infection in the joint.

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Signs and symptoms typically include:

  • Swelling. This is clearly shown by the skin on the knee cap puffing up.
  • Stiffness. When your knee joint contains excess fluid, you might not be able to bend or straighten your leg completely.
  • Pain. Depending on the cause of the fluid build-up, your knee might be very painful – to the point that it’s impossible to bear weight on it.


Many types of problems, ranging from traumatic injuries to diseases and other conditions, can cause a swollen knee.


Damage to any part of your knee can cause excess joint fluid to accumulate. Injuries that can cause fluid build-up in and around the knee joint include:

  • Torn ligament, particularly the anterior cruciate ligament (ACL).
  • Cartilage (meniscus) tear.
  • Irritation from overuse.
  • Broken bones.
  • Anterior cruciate ligament (ACL injury): The anterior cruciate ligament (ACL) is one of the key ligaments that help stabilise the knee joint. It connects the thigh bone (femur) to the shin bone (tibia). It is most commonly torn during sports that involve sudden stops and changes in direction or twisting, such as basketball, soccer, tennis and volleyball.
  • Torn meniscus: The meniscus is a C-shaped piece of tough, rubbery cartilage that acts as a shock absorber between the shin bone and the thigh bone. It can be torn if you suddenly twist your knee while bearing weight on it.

Diseases and conditions

Underlying diseases and conditions that can produce fluid build-up in and around the knee joint include: .

  • Rheumatoid arthritis.
  • Osteoarthritis.
  • Infection.
  • Gout.
  • Pseudo-gout.
  • Bursitis.
  • Cysts.
  • Tumours.

Risk factors

Factors that may increase your risk of a swollen knee include:

  • Age. Your likelihood of developing a swollen knee related to arthritis increases as you age.
  • Sports. People who participate in sports that involve twisting the knee, such as basketball, are more likely to experience the types of knee injuries that cause swelling.
  • Obesity. Excess weight puts added stress on the knee joint, contributing to the tissue and joint overload and knee degeneration that can lead to a swollen knee.


Complications of a swollen knee can include:

  • Muscle loss. Fluid in the knee can harm the working of your muscles and cause thigh muscles to weaken and atrophy.
  • Fluid-filled sac (Baker cyst). The build-up of fluid in your knee can lead to the formation of a Baker cyst in the back of your knee. This can be painful, but usually improves with icing.


A swollen knee is typically the result of an injury or chronic health condition. To manage your overall health and prevent injuries:

  • Strengthen the muscles around your knee. Strong muscles around a joint can help ease pressure on the joint itself.
  • Choose low-impact exercise. Certain activities, such as water aerobics and swimming, don’t place continuous weight-bearing stress on your knee joints.
  • Maintain a healthy weight. Excess weight contributes to the wear-and-tear damage that can lead to a swollen knee


Your health care provider is likely to start with a detailed history and physical examination. After that you likely will need tests to find out what’s causing your swollen knee.

Imaging tests

These tests can help show where the problem is located. Options include:

  • X-ray. An X-ray can rule out broken or dislocated bones and determine if you have arthritis.
  • Ultrasound. This test uses sound waves to check for disorders.
  • MRI. This can detect tendon, ligament and other soft tissue injuries not visible on X-rays.

Joint aspiration (arthrocentesis)

A needle is used to remove fluid from inside your knee. This fluid is then checked for the presence of:

  • Blood, which may stem from injuries or bleeding disorders
  • Bacteria that may be causing an infection
  • Crystals common to gout or pseudo-gout.


Treatment varies depending on the cause of the swollen knee, its severity and your medical history.


Physical therapy exercises can improve your knee’s function and strength. In some situations, a knee brace may be helpful.

Surgical and other procedures

Treating the underlying cause might require:

  • Arthrocentesis. Removing fluid from the knee can help relieve pressure on the joint. After removing some of the joint fluid, your doctor might inject a corticosteroid into the joint to treat inflammation.
  • Arthroscopy. A lighted tube (arthroscope) is inserted through a small incision into your knee joint. Tools attached to the arthroscope can remove loose tissue or repair damage in your knee.
  • Knee replacement. Physical exercises can improve your knee’s function and strength. In some situations, a knee brace may be helpful.

Home care

Taking care of yourself when you have a swollen knee includes:

  • Rest. Avoid weight-bearing activities as much as possible.
  • Ice and elevation. To control pain and swelling, apply ice to your knee for 15 to 20 minutes every two to four hours. When you ice your knee, be sure to raise your knee higher than the level of your heart. Place pillows under your knee for comfort.
  • Compression. Wrapping your knee with an elastic bandage can help control the swelling.
  • Pain relievers. Over-thecounter medicines such as acetaminophen (Tylenol and others with same active ingredient) or ibuprofen (Advil, Motrin IB and others) can help reduce the swelling on your knee. If these don’t help, see your doctor.

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