Pyogenic Arthritis (Septic Arthritis)

Clinical assessment

Suspect based on acute onset of a painful, swollen, warm joint with restricted movement, often with fever. Differentiate from inflammatory arthritis (e.g., gout, RA flare, reactive arthritis), haemarthrosis (bleeding into joint - haemophilia, trauma), trauma, adjacent osteomyelitis.

Investigations

• Joint Fluid Aspiration (Arthrocentesis): Crucial diagnostic test. Send fluid for: Gram stain, Cell count and differential (typically high WBC count >50,000/mm³ with neutrophil predominance), Crystal analysis (rule out gout/pseudogout), Culture and Sensitivity (bacterial, fungal, TB if suspected).
• Blood tests: Full Blood Count (leucocytosis), ESR/CRP (usually markedly elevated), Blood cultures (may be positive, obtain before antibiotics).
• Imaging (X-ray, Ultrasound, CT/MRI): X-ray often normal early, may show soft tissue swelling, later joint space widening/narrowing, erosions. Ultrasound can detect effusion, guide aspiration. CT/MRI better for assessing bone involvement/osteomyelitis.

Diagnostic criteria

Clinical suspicion + Positive Gram stain or Culture from synovial fluid OR Clinical suspicion + Purulent synovial fluid (high WBC count) even if Gram stain/culture negative.

Non-pharmacological management

• Joint Drainage: Essential to remove pus and reduce pressure.
• - Needle Aspiration: Repeated daily until fluid no longer re-accumulates.
• - Arthroscopic Lavage/Drainage or Open Surgical Drainage (Arthrotomy): If needle aspiration ineffective, loculated effusion, hip joint involvement, or prosthetic joint infection.
• Immobilisation: Splint the joint in a functional position during acute phase for pain relief.
• Physiotherapy: Early passive range of motion exercises once inflammation starts subsiding, progressing to active exercises to restore function and prevent contractures.

Pharmacological treatment

• Analgesia: Paracetamol, NSAIDs (Ibuprofen, Diclofenac, Indomethacin) for pain and inflammation. Opioids if severe pain.
• Antibiotics: Start IV antibiotics immediately after joint aspiration, tailored based on Gram stain initially, then culture/sensitivity results. Prolonged course required (e.g., 2-4 weeks IV followed by 2-4 weeks oral, total 4-6 weeks or longer).
• - Empirical (Gram stain negative/pending, immunocompetent adult): Cloxacillin IV 1-2g Q6H (Child: 50mg/kg Q6H).
• - Gram Positive Cocci: Cloxacillin (or Vancomycin if MRSA suspected/prevalent).
• - Gram Negative Bacilli: Ceftriaxone IV 1-2g daily (Child: 50-80mg/kg daily) OR Ciprofloxacin (adults).
• - Underlying conditions / Child / Negative stain: Consider broader coverage initially (e.g., Cloxacillin + Ceftriaxone).
• - Suspected Gonococcal Arthritis (sexually active adolescent/adult): Ceftriaxone IV/IM.
• - Switch to appropriate oral antibiotics based on sensitivity and clinical improvement.

Monitoring

Monitor clinical response (pain, swelling, fever, range of motion). Monitor inflammatory markers (ESR/CRP). Monitor joint fluid aspirate volume and cell count if repeated aspirations done. Monitor antibiotic levels/side effects if applicable (e.g., Vancomycin, Aminoglycosides).