Fluid in the Knee
Fluid in the knee (also known as ‘water on the knee’ or ‘knee effusion’) is a condition resulting from excess fluid accumulation in or around the knee joint. The knee joint contains a small amount of fluid under normal conditions, within the joint itself and in surrounding tissues. When the fluid build-up is more than normal due to various conditions including disease and trauma, it leads to ‘water on the knee’.
The Anatomy of the Knee Joint
The knee joint is surrounded by a protective capsule lined by the synovial membrane, which forms a ‘joint space’. Normally, this capsule has a small amount of fluid called synovial fluid, which acts as a lubricant and reduces friction between the bones as they move. In response to inflammation of the tissues or any trauma, the protective capsule releases more synovial fluid, which can lead to accumulation of this fluid.
Another source of fluid in the knee joint is a large bursa located within the knee joint. Several conditions can lead to inflammation of this bursa (bursitis), and cause it to become distended with synovial fluid or blood, which again leads to ‘fluid in the knee’.
What are the causes of ‘Fluid on the knee’?
Water on the knee can be caused by trauma, overuse injuries, or an underlying disease or condition. The type of fluid that accumulates depends on the underlying condition. To determine the exact cause of the fluid buildup, doctors need to test a sample of the fluid for infection, disease or injury.
Some of the underlying conditions leading to fluid accumulation may include:
- Direct trauma to the knee
- Overuse injuries
- Ligament tears
- Rheumatoid Arthritis
What are the symptoms of ‘Water on the Knee’?
The actual symptoms of water on the knee will depend on the cause of the excess fluid build-up in the knee joint. Some common signs and symptoms of ‘water on the knee’ typically include:
- Swelling of the knee is one of the main symptoms of fluid accumulation. Usually, the kneecap area swells up noticeably.
- Pain in the knee is quite common with this condition. Depending on the cause of the fluid buildup, the knee may be very painful. In severe cases, it might be impossible to stand, walk or bear any weight on the knee. In cases of osteoarthritis, the pain occurs when bearing weight and subsides when resting.
- There may be considerable stiffness in the knee. Sometimes the puffed up knee may be difficult to straighten out or bend, and patients would have difficulty in simple tasks like sitting and standing up.
- One knee may appear larger than the other due to the fluid accumulation.
- In some cases, bruising may be present on the front, sides or rear of the knee.
How is This Condition Diagnosed?
Once the swelling is noticed, patients should visit their doctor to diagnose the underlying condition.
- To reach a diagnosis, a sample of the fluid is usually collected through a procedure known as ‘joint aspiration’ or arthrocentesis. This sample may be sent for cell count, culture (to test for infection) and examination of crystals (to check for gout).
- If the knee joint is swollen, red and warm to the touch, the doctor might also order blood tests.
- X-rays might also be ordered to check for fractures, dislocation or osteoarthritis.
- MRI may be used to check for abnormalities such as tears in the ligaments, tendons or cartilage.
How is this Condition Treated?
- The treatment of water on the knee will depend on the underlying cause of the swelling.
- Generally, removal of some of the fluid (by joint aspiration) may help reduce the pain and stiffness associated with water on the knee.
- Conservative treatment like rest, icing the knee joint, pain medications and restriction from activity usually help to resolve the symptoms of water on the knee.
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