A knee arthrocentesis is a minor surgical procedure to aspirate synovial fluid from the knee joint. The procedure has diagnostic and therapeutic uses as it drains fluid and diagnoses the etiology of the underlying knee pathology. During arthrocentesis, blood vessels, nerves, and tendons can always be injured. Clinicians with extensive knowledge of the knee's anatomy, training, and credentialing should perform the procedure.
The knee is the largest synovial cavity in the body and is easily accessible from either the medial or lateral aspect and superior or inferior to the midpoint of the patella. The patient can be supine or sitting, but fluid is more easily aspirated in the supine position. To minimize the risk of injury, the joint's surface should be in extension with minimal (20°) flexion under ultrasound guidance, as this approach improves aspiration volume, accuracy rates, and pain scores.
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