Knee inflammation

Knee inflammation means your knee joint is swollen, and often warm, red or stiff, because of an injury, overuse or an underlying condition. It's sometimes called a swollen knee, water on the knee, or knee effusion, when fluid builds up in or around the joint.

What causes knee inflammation?

Sudden swelling is usually caused by an injury, while swelling that builds up gradually is more often down to overuse or an underlying condition.

• Injury or trauma: Such as a fracture, ligament injury, meniscus (cartilage) tear, or dislocation of the kneecap
• Overuse: From repeated bending, kneeling, or activities like ladder climbing, stairs or sport, which can lead to bursitis (inflammation of the fluid-filled sacs that cushion the knee)
• Osteoarthritis: Age-related changes in the cartilage in the knee
• Other types of inflammatory arthritis: Including gout and rheumatoid arthritis
• Baker's cyst: A build-up of joint fluid at the back of the knee, often linked to another knee problem
• Bleeding into the joint (haemarthrosis): Usually after an injury, and needing urgent medical treatment
• Infection: Also known as septic or infectious arthritis, causing rapid swelling, redness, heat and fever, and needing urgent treatment.

Are there different types of knee inflammation?

Knee inflammation can be acute (coming on suddenly) or chronic (building up gradually and lasting a long time), and the pattern can offer a clue to the cause.

• Acute swelling: Comes on suddenly, often after an injury, and usually settles within a day or so with rest
• Chronic swelling: Builds up gradually and lasts longer, often linked to an underlying condition such as arthritis, and more common as you get older
• With redness, heat and fever: Can be a sign of infection or gout, and needs urgent medical attention
• Without other symptoms: Swelling on its own, especially after activity, is often a sign you've gone above your knee's current tolerance for load, rather than a sign of damage.

How is knee inflammation diagnosed?

Your doctor will usually ask about your symptoms and examine your knee. Diagnosis often doesn't need any tests, especially if osteoarthritis is the likely cause based on your age and symptoms. In some circumstances, the following investigations may be required to clarify the cause:

• X-ray: This is to look at the bones and the joint space
• Ultrasound or MRI scan: These can be used to examine soft tissue, such as ligaments, cartilage or fluid
• Joint aspiration: A fine needle is used to take a sample of fluid from the knee, to check for infection, gout crystals or blood
• Blood tests: These may be needed if an underlying condition such as inflammatory or infectious arthritis is suspected.

How is knee inflammation treated?

Treatment depends on the cause, but many of the same first steps help regardless of what's causing your swelling.

1. Rest: Reduce, rather than stop, your normal activity, and avoid anything that clearly makes the swelling worse
2. Ice: Apply a covered ice pack or a bag of frozen peas wrapped in a damp towel for 10–15 minutes every 2 hours for the first 48–72 hours
3. Painkillers: Paracetamol or ibuprofen, taken regularly, can help you keep moving – check with a pharmacist or GP first if you take other medicines
4. Elevation: Raise and support your leg to help reduce swelling
5. Gentle movement: After the first day or two, gentle bending and straightening, and gradually building back up to your normal activity, helps you recover and avoid stiffness.

Low-impact exercise, such as swimming, water aerobics or cycling, is often more comfortable than high-impact or twisting activities, and can help strengthen the muscles that support your knee.

If self-care does not help, or an underlying condition is found, further treatment might include physiotherapy, steroid injections, draining fluid from the knee with a needle, or in some cases, surgery such as knee arthroscopy or knee replacement.

When should you see a doctor?

Most knee swelling settles down on its own within a few days to about 6 weeks.

See a GP if:

• your swelling does not go down after a few days, or your pain lasts longer than about 6 weeks
• your knee is hot to touch, suddenly very swollen, or red – this can be a sign of infection or acute gout
• you have a fever, or feel generally unwell, alongside your knee symptoms, which is a sign of infection
• you cannot put weight on your leg, or your knee looks deformed
• there's significant swelling spreading beyond your knee into your leg
• you have constant pain at night that stops you sleeping, or unexplained weight loss
• there's been a new, significant injury, such as a fall from height or a direct blow to the knee, in the last few days.