Glossary
Joint aspiration (knee aspiration)
Quick answer
Joint aspiration, also called arthrocentesis or a knee tap, means drawing fluid out of a swollen knee through a needle. It relieves pressure and lets the fluid be tested for infection, crystals or blood, which can change the diagnosis quickly, explains Doha knee surgeon Dr. Pablo Gelber at Aman Hospital.
What it feels like
You lie with the knee straight and relaxed. The skin is cleaned and usually numbed with local anaesthetic. The needle is passed into the joint, typically beside the kneecap, and fluid is drawn into a syringe. Ultrasound may be used to guide it.
Most patients feel a sting, then pressure; many feel immediate relief as a tight, swollen knee softens. The procedure takes a few minutes. A small dressing is applied, and a steroid injection is sometimes given through the same needle if infection is not suspected.
What it tells the surgeon
Simply looking at the fluid is informative. Clear, straw-coloured fluid is typical of arthritis or a meniscus problem. Blood after an injury suggests an ACL tear, kneecap dislocation or fracture, and fat droplets in the blood point to a fracture. Cloudy fluid raises concern for inflammation or infection.
The sample is then sent for synovial fluid analysis, including cell count, crystals and culture.
Risks and aftercare
Serious complications are uncommon. Infection is the main concern, so a knee that becomes increasingly hot, red and painful, or a fever after aspiration, needs prompt review. Fluid can reaccumulate if the underlying cause is not treated.
Frequently asked questions
Will the fluid come back?
It can, because aspiration treats the swelling, not the cause. Treating the underlying problem, such as arthritis, a tear or gout, is what keeps it away.
Can I walk after a knee aspiration?
Yes. Most people walk out of the clinic. Avoid strenuous activity for a day or two and follow any specific advice from your surgeon.
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