Fluid on the knee, also known as a knee effusion, can result from various underlying causes. These causes often involve inflammation, injury, or underlying medical conditions that disrupt the normal fluid balance within the knee joint.
Here's a breakdown of the common ways fluid can accumulate in the knee:
Common Causes of Fluid on the Knee
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Osteoarthritis: This degenerative joint disease causes cartilage breakdown, leading to inflammation and excess fluid production.
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Rheumatoid Arthritis: This autoimmune disease causes chronic inflammation of the joint lining (synovium), resulting in fluid buildup.
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Infection (Septic Arthritis): Bacteria or other pathogens can infect the knee joint, triggering inflammation and fluid accumulation. This is a serious condition requiring prompt medical attention.
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Gout: The buildup of uric acid crystals in the joint can cause intense inflammation and fluid effusion.
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Pseudogout (Calcium Pyrophosphate Deposition Disease - CPPD): Similar to gout, calcium pyrophosphate crystals accumulate in the joint, leading to inflammation and fluid buildup.
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Bursitis: Inflammation of the bursae (fluid-filled sacs that cushion joints) around the knee can cause fluid to leak into the knee joint. Prepatellar bursitis ("housemaid's knee") and pes anserine bursitis are common examples.
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Cysts: Baker's cysts (popliteal cysts) are fluid-filled sacs that develop behind the knee, often due to underlying knee problems. If these cysts rupture, they can leak fluid into the surrounding tissues.
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Tumors: Though less common, tumors in or around the knee can also cause fluid accumulation.
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Trauma/Injury: Direct blows to the knee, ligament tears (ACL, MCL), meniscus tears, or fractures can all lead to inflammation and fluid buildup.
Summary
Fluid on the knee is typically a symptom of an underlying problem, such as arthritis, infection, injury, or other medical conditions. If you suspect you have fluid on your knee, it's crucial to consult a doctor for proper diagnosis and treatment.
