Water On The Knee (Knee Effusion): Treatment, symptoms, and causes

Knee effusion, or water on the knee, occurs when excess fluid accumulates in or around the knee joint. There are many common causes for the swelling, including arthritis and injury to the ligaments or meniscus (cartilage in the knee).

A small amount of fluid exists in normal joints. When a joint is affected by arthritis, particularly an inflammatory arthritis, such as rheumatoid arthritis (RA), abnormal amounts of fluid can build up, and the knee becomes swollen.

In this article, we will discuss the treatments, symptoms, and causes of water on the knee, and some ways to prevent it occurring.


Woman in exercise gear ready to go jogging.
Treatments for knee joint effusion may include gentle and regular stretches and exercises.

Most treatments for knee joint effusion are based on the cause of the condition, so treatment varies for each individual.

A physical therapist can advise on exercises and fitness activities to strengthen the area and support the weakened knee.

Sometimes, a series of corticosteroid injections is prescribed, non-steroidal anti-inflammatory drugs (NSAIDs), or antibiotics to reduce inflammation or treat an infection. For others, knee surgery or even joint replacement may be necessary.

Many people with water on the knee will need to have the excess fluid removed; this will be done by aspiration.

A traumatic right knee effusion. Photo credit: James Heilman, MD.
A traumatic knee effusion may be characterized by puffiness or swelling of the joint and surrounding area. Photo credit: James Heilman, MD.

Signs and symptoms of water on the knee depend on the cause of excess fluid build-up in the knee joint.

If it is caused by osteoarthritis, pain occurs when bearing weight. This pain typically subsides with rest and relaxation.

One knee may appear larger than the other. Puffiness around the bony parts of the knee appears prominent when compared with the other knee.

When the knee joint contains excess fluid, it may become difficult to bend or straighten the knee.

If the knee effusion is due to an injury, there may be bruising on the front, sides, or rear of the knee. Bearing weight on the knee joint may be impossible and the pain unbearable.

Home remedies

Along with any kind of medical care, knee joint effusion responds well to simple self-care measures, such as rest and elevation, ice and suitable exercise.

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