Aspiration of the knee is the removal of fluid from inside the joint, using a needle and syringe.

Page updated September 2023 by Dr Sheila Strover (Clinical Editor)


How and why knee aspiration is performed

To aspirate the knee, the practitioner prepares the joint with a sterilising fluid and clean drapes, and palpates with gloved hands on the lateral side just under the kneecap. If the knee is full of fluid the examining finger should feel a 'bounce' in this area, where a wide syringe needle can be introduced, and the fluid withdrawn.

The fluid may be:

  • an excess of joint fluid - where irritation has caused an effusion
  • blood - where there has been an haemarthrosis
  • pus - where the joint is infected
  • a fatty fluid - in cases where a fracture has involved the joint cavity

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Dr Sheila Strover (Editor)
BSc (Hons), MB BCh, MBA

See biography...