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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.

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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.

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.

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.

As with any injury, ice should be applied to the affected area only for 15 to 20 minutes at a time, and never directly onto the skin. Place the ice pack in a towel or cloth.

Over-the-counter (OTC) medication, such as acetaminophen (Tylenol) may help relieve the pain.

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

Causes of the swelling include arthritis or an injury to the ligaments of the knee.

After an injury, swelling occurs because the body’s natural reaction is to surround the knee with a protective fluid. This is to prevent further damage.

Knee effusion could also be caused by an underlying disease or condition.

The type of fluid that accumulates around the knee depends on the underlying disease, condition, or type of traumatic injury that caused the excess fluid. The swelling can, in most cases, be easily cured.

Having osteoarthritis or engaging in high-risk sports that involve rapid cut-and-run movements of the knee (like football or tennis), means an individual is more likely to develop water on the knee.

Excess weight and obesity place more weight on the knee, causing more wear in the joint. Over time, the body will produce excess joint fluid.

Recovery time depends on the cause and treatment of knee effusion.

A patient who undergoes aspiration should use a small bandage to keep the area dry and clean.

Heavy exercise, such as jumping, should be avoided for the first 2 days, or for as long as the doctor recommends.

Some people continue to experience pain. If this happens, a doctor will prescribe medication to relieve it.

Avoiding sudden jolting movements and rough running surfaces can help prevent knee injuries. Obesity adds pressure to the vulnerable knee joint, so weight reduction may help.

Exercises considered better for the knees include small (not deep) knee bends and straightening motions done with most weight on the outside of the foot.

Sports that are easier on the knees include walking, swimming (flutter kicks, knees straight), skating, baseball, cross-country skiing, and, depending on the state of the knee, cycling (seat high, low gear, and avoiding hills).

Choose activities to suit your own knee strength and capacity, and remember that sports especially hard on the knees include football, sprinting, soccer, rugby, hockey, squash, volleyball, basketball, downhill skiing, tennis, and jogging or anything that pounds, jolts, or twists the knees.