Knee Joint Aspiration (Arthrocentesis): Procedure & What to Expect

Knee arthrocentesis drains excess synovial fluid (effusion) via needle under ultrasound guidance.

Step-by-Step

1. Position: Supine, knee flexed 15–30° (towel under knee).
2. Prep: Sterile skin prep (chlorhexidine); local anesthetic (1% lidocaine) at entry site.
3. Ultrasound: Identifies fluid pocket, avoids vessels/nerves.
4. Needle insertion: 18–20G needle, lateral or medial parapatellar approach.
5. Aspiration: Syringe draws fluid (often 20–100+ mL).
6. Analysis: Cell count, crystals (gout/pseudogout), culture, glucose, protein.
7. Injection (optional): Corticosteroid ± anesthetic after drainage.
8. Bandage: Sterile dressing; ice, elevation post-procedure.

Indications

• Diagnostic: unexplained effusion, suspected septic/inflammatory arthritis.
• Therapeutic: tense painful effusion, pre-op decompression.

Quick (10–15 min), low-risk; complications rare (infection, bleeding, nerve injury).