Makindo Medical Notes

💉 Joint Aspiration (Arthrocentesis)

Joint aspiration is both a diagnostic and therapeutic procedure used to assess synovial fluid and relieve joint pressure. Always consult orthopaedics before aspirating any prosthetic joint to avoid introducing infection. The key aim is to exclude sepsis and identify inflammatory, crystal, or haemorrhagic causes of joint swelling. 🦵

⚕️ Indications

• Suspected septic arthritis (urgent diagnostic indication).
• Assessment of inflammatory arthritis (RA, gout, pseudogout).
• Haemarthrosis following trauma or anticoagulation.
• Symptomatic relief of tense effusion.
• Therapeutic injection — corticosteroid or local anaesthetic.

🧫 Laboratory Analysis

• Macroscopic appearance: colour, clarity, and viscosity (string test for hyaluronic acid content).
• Microscopy: WBC count, differential, Gram stain, and crystal analysis.
• Biochemical tests: glucose and protein levels (compare to plasma).
• Culture and sensitivity: to identify infective organisms.

🧍‍♂️ Procedure (Trained Operators Only)

• Explain the procedure and gain consent.
• Aseptic technique: use sterile gloves, drapes, and antiseptic (chlorhexidine, betadine, or alcohol).
• Position the joint to maximise access to the joint capsule.
• Local anaesthesia: inject lidocaine subcutaneously to create a wheal.
• Needle size: typically 18G for large joints (knee); smaller for small joints. Use a spinal needle for deep joints (hip, shoulder).
• Insert at the recommended anatomical landmark (see below examples):
• Knee: superolateral or medial to the patella, directed posteriorly and slightly downward.
• Elbow: lateral “soft spot” between the olecranon, lateral epicondyle, and radial head.
• Ankle: just medial to the tibialis anterior tendon.
• Apply negative pressure with a 10–20 mL syringe to aspirate fluid.
• Transfer samples to sterile containers for microbiology, cytology, and crystal analysis.
• Clean and apply a pressure dressing to reduce reaccumulation.
• Observe for post-procedure bleeding, infection, or syncope.

🔬 Synovial Fluid Interpretation

💎 Crystal Analysis

• Monosodium urate crystals: needle-shaped, negatively birefringent under polarised light → Gout.
• Calcium pyrophosphate dihydrate (CPPD) crystals: rhomboid, positively birefringent → Pseudogout.

⚠️ Safety and Precautions

• Avoid in overlying cellulitis or uncorrected coagulopathy.
• Always exclude sepsis before injecting corticosteroids.
• Do not aspirate prosthetic joints unless under orthopaedic supervision.
• Send all samples urgently — organisms may degrade within 1 hour.

📚 References

• NCBI: Synovial Fluid Analysis
• British Society for Rheumatology. Joint Aspiration and Injection Best Practice Guidelines, 2021.

🧠 Teaching tip: A turbid, yellow, low-viscosity aspirate with high WBC (>50,000) and neutrophil predominance almost always means septic arthritis — a true emergency. Start IV antibiotics immediately after sending cultures and involve orthopaedics urgently. 🚨