What causes the symptom of joint effusion?

Joint effusion, also known as synovial effusion or water on the knee, is a condition in which excess synovial fluid accumulates within a joint, causing swelling and discomfort. The fluid is produced by the synovial membrane, which lines the joint capsule, and serves to lubricate and cushion the joint during movement.

A variety of factors can cause joint effusion, with some of the most common including:

1. Trauma: Injuries to the joint, such as sprains, fractures, or dislocations, can damage the synovial membrane, leading to increased fluid production and effusion.

2. Inflammatory Conditions: Joint effusion is a common symptom of inflammatory conditions such as rheumatoid arthritis, gout, and osteoarthritis. These conditions cause inflammation of the synovial membrane, resulting in excessive fluid production.

3. Infection: Infections of the joint, such as septic arthritis, can also cause joint effusion. The inflammatory response to the infection leads to increased production of synovial fluid.

4. Overuse: Repetitive stress or overuse of a joint, particularly in athletes or individuals engaged in strenuous physical activity, can strain the synovial membrane and cause effusion.

5. Baker's Cyst: A Baker's cyst is a fluid-filled sac that develops behind the knee joint. It can cause joint effusion by pressing on the synovial membrane and obstructing the flow of synovial fluid.

6. Underlying Medical Conditions: Certain medical conditions, such as heart failure, liver cirrhosis, and kidney failure, can lead to fluid retention and joint effusion.

It's important to note that joint effusion can be a symptom of an underlying medical condition, so it's essential to seek medical evaluation if you experience persistent or unexplained joint swelling and discomfort. A doctor can determine the cause of the effusion and recommend appropriate treatment.