Also known as “knee effusion”, water on the knee is a condition in which excess fluid accumulates around your knee joint.

Your knee is contained within a membrane that normally contains less than one ounce of lubricating joint fluid. Various injuries and illnesses can cause extra fluid to build up around your joint.

What are the most common reasons for getting water on the knee?

Inflammation from Overuse

  • Significant “wear and tear”


  • Sudden stop or direct blow to the knee
  • Twisting
  • Hyperextension

Chronic Health Conditions

  • Osteoarthritis is the most common cause. This happens when your meniscus wears away from repetitive stress and/or injury. When you don’t have the lubricating effect of cartilage, the friction increases, and your knee becomes swollen and painful.


  • Infections such as tuberculosis, Lyme disease, brucellosis, and gonorrhea
  • Gout – when you have too much uric acid in your blood, the acid can crystallize in your joints
  • Rheumatoid arthritis – an autoimmune disease where your immune system attacks your cells
  • Bursitis – when the small, fluid-filled sacs that separate your knee bones from muscles and tendons swell
  • Tumors – benign and cancerous masses can sometimes infiltrate your knee

How do I know if I have water on the knee?

  • Does the skin around your kneecap look and feel puffy?
  • Do you have mild to severe pain?
  • Do you have stiffness? Is it hard to completely straighten or bend your knee?
  • Do you notice clicking or locking of the knee?
  • Are you having trouble walking or putting weight on your knee?

Is it dangerous to have water on the knee?

No, it is not usually dangerous, however, it may be a sign of a more serious medical condition, as mentioned above. Also, if the swelling lasts for a long time, it can cause your leg muscles to weaken, which can put older people more at risk for falling. Some people may also suffer from a fluid-filled sac that forms on the back of the knee, called a Baker’s cyst. This has the potential to become quite a nuisance, requiring draining by a doctor.

How can I have this treated?

First, it needs to be determined by a doctor what is causing the water on the knee. Then, the goal would be to reduce swelling, relieve pain, improve function, and treat whatever underlying illnesses that may be causing this.

This would be done through:

  • Medications to fight inflammation (oral or injections)
  • Arthocentesis – your doctor would use a needle to draw fluid from your joint to relieve pressure and pain.
  • Arthroscopy – your doctor would thread a tube with a camera on the end into your knee. Tools could then be passed through the tube to remove loose tissue and repair cartilage damage.
  • Complete joint replacement – a surgeon would replace your knee joint with a prosthetic.

Can my physiotherapist help?

Absolutely! Your physio can help with treatments that include icing, splinting, and ultrasound to promote healing, as well as instruct you on exercises that can improve your range of motion and strength. If you have total knee replacement surgery, a physiotherapy program would be required to help get you back to your normal function and activity.

Do you suffer from water on the knee? Have you undergone a total knee replacement? Book an appointment at Dunbar Physio and we can help get you onto the road of recovery!