Swollen Knee

Several common conditions can cause a swollen knee joint. It can come on gradually as part of a chronic condition or suddenly from an acute event or injury. If your knee is swollen and you’re not sure why or would like some help, find out more below.

Causes of a swollen knee


Arthritis is a common cause of a swollen knee, as the body produces extra fluid within the joint. How much fluid is produced changes over time and can be related to activity, so using the knee more (such as when walking, gardening or climbing stairs) will often cause more swelling.


Prepatellar bursitis happens when fluid accumulates in the bursa, a thin fluid-filled sack, which sits on top of the patella (knee cap) outside the knee joint.

This can be caused by trauma or overuse, resulting in pain and swelling on the knee cap.

Symptoms of bursitis include:

  • Dull, achy pain
  • Skin feels tender or warm
  • Swelling
  • More painful when you move your knee of press on it
  • Redness – this may be harder to spot on darker skin

If you still have a swollen knee after resting the joint, it’s a good idea to see a doctor. They will take a sampleof the fluid and test it for infection or other conditions, such as gout. If you have an infection, this can be treated with antibiotics. If your bursitis is not caused by an infection, you may be given a steroid injection in your joint to help reduce the swelling. If your bursitis is severe, or keeps coming back, you may need it surgically drained. This is a simple procedure which can be done in outpatients. In rare cases, you may need your bursa completely removed.


Gout is caused by a build-up of uric acid crystals in the joints. Common symptoms of gout are an inflamed, swollen knee and sudden, severe pain. Pseudogout has a similar presentation but is caused by a build-up of calcium crystals.

People who suffer from gout often have acute episodes, with swelling starting suddenly in one or more joint (usually the big toe). This can be triggered by alcohol and certain foods or medicines, but it can also have no apparent cause.

Gout is diagnosed by removing a small fluid sample for analysis to see if it contains crystals.

Once your consultant has diagnosed gout or pseudogout, they can provide advice and prescribe  anti-inflammatories and other medicines for mild attacks, as well as offer injection therapies for moderate or severe cases.


Trauma to the knee can result in a swollen knee, which will come on quickly over 24 hours. Your knee will be investigated, and a sample of the fluid will be taken to see if it contains blood.

The most common causes of blood in the knee are torn ligaments, most frequently the ACL, or a fracture. In these cases, swelling will occur within minutes of the injury.

If there is no blood in the fluid, this can indicate a meniscal tear or a ligament sprain. In these cases, the swelling will start quickly within hours of the injury.

If you’ve injured your knee, it’s a good idea to see a doctor who can check for damage and test if there is blood in the fluid. Surgery is not always required, and your consultant will advise you on the most suitable investigation and treatment plan for the type of injury you’ve sustained and your activity levels.

Get in touch about swollen knee treatment

If you’re worried about your swollen knee and would like to ask any questions or book an appointment, contact our specialist team.

Our friendly team will do their best to = find you the earliest appointment possible with the best specialist for your needs.

Knee Clinic

The Knee Unit at St John & St Elizabeth Hospital comprises a dedicated team specialising in the diagnosis and treatment of knee pain and stiffness caused by knee conditions or injuries.

A patient speaking to a receptionist

Patient information

Our Hospital is renowned for providing exemplary levels of care across more than 90 services. From orthopaedics, to urology, our private GP practice and Urgent Care Clinic, our services are led by some of London’s leading Consultants. For more information, and to find a service suitable for your care, find out more about the services that we offer.

Make an enquiry

If you have any questions relating to treatment options or pricing information, get in touch with us by filling out one of our contact boxes or giving us a call on 020 7432 8328.

Our Appointments Team have a dedicated and caring approach to finding you the earliest appointment possible with the best specialist.

If you are self-paying you don’t need a referral from your GP for a consultation. You can simply refer yourself* and book an appointment.

If you have health insurance (e.g. Bupa, Axa Health, Aviva), you will need to contact your insurer to get authorisation before any treatment, and in most cases you will also require a referral letter from your GP.

If you are not registered with a GP, we have an in-house private GP practice you can use. Alternatively, we can suggest the most appropriate course of action for you to take, given your location and individual circumstances.

*Please note – for investigations such as X-rays and MRIs, a referral will be required. However, we may be able to arrange this for you through our on-site private GP.

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