Joint aspiration and injection
Also known as: arthrocentesis, joint tap, steroid injection, knee aspiration, synovial fluid analysis
A needle is passed into a swollen joint to draw off fluid for analysis and to relieve pressure, often followed by an injection of corticosteroid and local anaesthetic through the same needle to settle inflammation. The knee is the commonest site; the shoulder, wrist, elbow, ankle and hip (with ultrasound guidance) are also done.
What it is
A needle is passed into a swollen joint to draw off fluid for analysis and to relieve pressure, often followed by an injection of corticosteroid and local anaesthetic through the same needle to settle inflammation. The knee is the commonest site; the shoulder, wrist, elbow, ankle and hip (with ultrasound guidance) are also done.
Why it is done
- A hot, swollen joint where septic arthritis must be ruled out (the fluid goes for urgent microscopy and culture)
- Diagnosing gout and pseudogout by finding crystals under polarised light
- Relieving a tense, painful effusion after injury or in osteoarthritis
- Steroid injection for osteoarthritis flares, rheumatoid arthritis, frozen shoulder, bursitis and tendon sheath inflammation
Before the procedure
- Explain and consent; check for anticoagulants (not a contraindication for most joints), skin infection over the site, and allergy
- Position the joint: the knee slightly bent over a roll; the landmark chosen beside the patella
- Skin cleaned with antiseptic; sterile gloves; local anaesthetic to the skin optional
Step by step
- A needle (18-21 gauge) on a syringe is advanced through the skin into the joint space using landmarks or ultrasound, with a giving-way as it enters
- Fluid is aspirated: its colour and clarity noted (clear yellow, cloudy, bloody, pus)
- Samples are sent for cell count, Gram stain and culture, and crystal examination
- If indicated, the syringe is swapped and steroid (for example 40 mg methylprednisolone or triamcinolone) with lidocaine is injected
- The needle is withdrawn and a dressing applied; the fluid volume is recorded
Afterwards
- Rest the joint for 24-48 hours after a steroid injection; ice for discomfort
- Watch for a flare of pain in the first day (crystal reaction to the steroid) and for redness, fever or increasing pain suggesting infection
- Diabetics: blood glucose may rise for a few days
Recovery
Relief from an aspiration is immediate; steroid benefit builds over a few days and lasts weeks to months.
Risks
- Introducing infection into the joint (about 1 in 10,000 with sterile technique)
- Bleeding into the joint, especially on anticoagulants
- Post-injection flare, skin thinning or pale patch at the site, facial flushing
- Cartilage damage with repeated steroid injections (limit to 3-4 a year)
Alternatives
- Oral anti-inflammatories and rest
- Physiotherapy and bracing
- Ultrasound-guided injection for deep or difficult joints
- Arthroscopy for mechanical problems