Water on the knee (knee effusion): causes, symptoms and treatments


Water on the knee (knee effusion): causes, symptoms and treatments

Knee effusion, colloquially known as 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, injury to the ligaments or meniscus, or when fluid collects in the bursa. This condition is known as prepatellar bursitis.

According to Medilexicon's medical dictionary, knee effusion is "a large bursa between the inferior part of the femur and the tendon of the quadriceps femoris muscle. It usually communicates with the cavity of the knee joint and is pathologically distended with blood or synovial fluid in suprapatellar bursitis ('water on 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), increased abnormal amounts of fluid buildup, the knee appears swollen. The fluid is produced by the tissues that are affected by the arthritis and that line the joint.

Symptoms of knee effusion

A symptom is something the patient senses and describes, while a sign is something other people, such as the doctor notice. For example, drowsiness may be a symptom while dilated pupils may be a sign.

A traumatic right knee effusion. 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. With osteoarthritis, pain occurs when bearing weight. The 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 in certain cases.

If an individual has injured his or her knee, he or she may note bruising on the front, sides or rear of the knee. Bearing weight on the knee joint may be impossible and the pain unbearable.

Causes of knee effusion

Causes of the swelling can include arthritis, injury to the ligaments of the knee or an accident after which the body's natural reaction is to surround the knee with a protective fluid.

A diagram of the knee

There could also be 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, football or tennis for example, means an individual is more likely to develop water on the knee.

In overweight or obese individuals the body places more weight on the knee joint. This causes more wear in the joint. Over time, the body will produce excess joint fluid.


On the next page we look at diagnosing water on the knee (knee effusion), the treatments for knee effusion and how it can be prevented.

  • 1
  • 2
  • NEXT PAGE ▶

Swelling Knee Joint Fluid Build up treatment for water on the knee (Video Medical And Professional 2020).

Section Issues On Medicine: Medical practice