Water on the Knee

Water on the knee (or fluid on the knee) is a generic term for swelling in or around the knee joint caused by an excessive accumulation of fluid.

The lining of the knee joint capsule, which encloses the knee joint, produces fluid that helps lubricate the moving parts of the knee joint and nourishes the cartilage.

Certain diseases and injuries cause excessive joint fluid to be produced. Knee osteoarthritis and knee injuries (acute traumatic injury or overuse injury) are the most common causes of water on the knee. Infection or inflammatory diseases may also cause fluid on the knee.

Consult a physician to rule out infection and to receive a proper diagnosis. An infection can cause severe, permanent damage to the knee joint if not treated early.

An accumulation of fluid within a joint cavity is also called a joint effusion. In the case of a traumatic injury, joint fluid may contain blood. If infection is involved, the fluid may contain pus. In gouty arthritis, there may be irritating uric acid crystals in the joint fluid. In inflammatory conditions such as rheumatoid arthritis, the fluid contains elevated levels of white blood cells.

Knee swelling is not always caused by excessive fluid within the joint capsule (joint effusion). Swelling may also be on the outside of the knee joint. Bursitis is a common condition that causes swelling on the outside of the knee joint. Swelling on the back of the knee may be a Bakers cyst.

Water on the knee may be an acute or chronic problem.

Symptoms of Water on the Knee

The swelling, which may or not be visible, causes a feeling of tenseness of the knee. There may be an inability to completely straighten the knee. Pain is often, but not always, present.

Other symptoms vary, depending upon the cause of the swelling. When water on the knee is caused by osteoarthritis, walking or standing is particularly painful (when the knee bears the weight of the body). When inflammation is involved, the knee may be swollen, hot, red, and painful. If inflammation and pain develop rapidly and there has not been an injury, there may be a bacterial infection in the knee joint.

Common Causes of Water on the Knee

Knee Injuries

Acute or overuse knee injuries may result in water on the knee. Swelling occurs as a result of leakage of fluid from damaged tissue. Bleeding may also occur from ruptured capillaries, resulting in swelling and discoloration (bruising).

Damaged tissue releases chemicals that initiate inflammation. Inflammation involves the dilation of capillaries (tiny blood vessels) and leakage of fluid from the capillaries, and the stimulation of nerve endings - causing heat, redness, swelling, and pain.

Acute injuries that often result in water on the knee include fractures, torn cartilage, or torn ligaments. A torn meniscus or torn ACL are the most common acute knee injuries resulting in water on the knee.

Overuse injuries may also lead to water on the knee. Kneecap bursitis (prepatellar bursitis) is usually caused from overuse, especially excessive kneeling. The swelling is not inside the knee joint itself but in the bursa in front of the kneecap. (A bursa may also become infected and cause pus to form).

See Knee Injuries page.

Arthritis of the Knee

Osteoarthritis is a degenerative disease involving the breakdown of joint cartilage. Osteoarthritis is the most common type of arthritis and the knee is the most common location for osteoarthritis. Knee osteoarthritis is the most common cause of water on the knee. The damage within the knee joint irritates the joint lining (the synovium) and causes excess amounts of synovial fluid to be produced. (Synovial fluid is a thick, sticky gel-like fluid that helps lubricate moving parts of a joint and nourish cartilage).

See Knee osteoarthritis page.

Gout is caused by a buildup of uric acid crystals in the joint, which fluid triggers inflammation of the joint. Gout occurs most commonly in the big toe, knee, wrist, or elbow. The affected joints are hot and red and well as swollen and painful.

Rheumatoid arthritis, an inflammatory autoimmune disease, involves inflammation of the joint lining. Many joints are often involved. Rheumatoid arthritis usually affects the joints of the hands, wrists and feet but may occur in many other joints. The knees are affected in up to one-third of people with this disease. Rheumatoid arthritis usually involves the same joints on both sides of the body.

Symptoms include pain and stiffness, which is worst in the morning, and swelling, warmth and redness of the affected joints. Rheumatoid arthritis affects the entire body and often causes fatigue.

Infectious arthritis may be caused by bacteria, a virus, or fungi. Bacteria in the bloodstream can spread to a joint and cause infectious arthritis. Bacteria may also enter from a wound. The knee is the most common location for bacterial arthritis. Conditions that increase the risk of joint infection include diabetes, rheumatoid arthritis, and other autoimmune disorders. People taking prednisone (corticosteroids) have an increased risk of infection although prednisone can mask the symptoms of infection.

Symptoms of a joint bacterial infection include acute onset of joint inflammation (pain, swelling, warmth and redness of the knee), fever, chills, general weakness, muscle aches, dizziness, and headache. Infectious arthritis caused by bacteria (also called septic arthritis or bacterial arthritis) requires prompt treatment with antibiotics. If not treated early, severe and permanent damage to the joint can occur. The infection may also spread.

Viral infections usually resolve by themselves and usually do not damage the joint. Antibiotics are ineffective against viruses.

Chondromalacia, a condition affecting the cartilage on the under surface of the kneecap, may also cause knee effusion.

Treatment of Water on the Knee

Treatment of water on the knee depends upon the cause. Treatment involves treating the underlying condition and the swelling.

If the swelling is particularly painful, the fluid may be aspirated from the knee for quick relief. However, depending on the situation, fluid may re-accumulate. An injection of corticosteroids (a powerful anti-inflammatory) is sometimes given, depending upon the underlying problem. If infection is suspected, aspirating the fluid can confirm infection and identify bacteria involved to determine the appropriate antibiotic/s to be used in treatment. Prompt treatment with antibiotics is necessary if infection is involved.

Reducing activity that causes pain, applying ice wrapped in cloth for 15 to 20 minutes every couple of hours, elevating the knee above the level of the heart (lying down with the knee on a pillow), and lightly wrapping the knee with an elastic bandage helps reduce pain and inflammation. If wrapped too tight, circulation to the lower legs and feet could be cut off. If the feet turn blue or cold, remove the bandage. The bandage should be removed before bedtime.

NSAIDs (non-steroidal anti-inflammatories) reduce both pain and inflammation and are usually well-tolerated for short-term use. Long-term use can cause ulcers in some people. Analgesics, such as Tylenol, reduce pain but do not reduce inflammation.

Always consult a physician to rule out infection and to receive a proper diagnosis.

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