Related Subjects:
|Monoarticular arthritis
|Polyarticular arthritis
|Rheumatoid arthritis
|Gout
|Pseudogout
|Septic Arthritis
|Osteomyelitis
|Systemic Lupus Erythematosus (SLE)
|Enteropathic Spondyloarthritis
|Reactive Arthritis
🔥 Septic arthritis is an orthopaedic and medical emergency that can rapidly destroy cartilage and lead to systemic sepsis.
Typically monoarticular, but polyarticular involvement is more common in immunocompromised patients.
Most cases are bacterial 🦠 (S. aureus most common), though fungal and mycobacterial infections occur in immunosuppressed or endemic populations.
Prosthetic joint infections require urgent orthopaedic input 👨⚕️🦴. Early recognition and intervention are critical to prevent permanent joint damage.
⚡ Key Facts for Students
- Monoarthritis = septic until proven otherwise 🚨.
- Pus within a joint releases proteases and cytokines → cartilage destruction within hours 🧪.
- Rapid joint aspiration, empiric antibiotics, and washout are essential.
- Hip & shoulder are high-risk joints due to poor collateral circulation.
- Always consider immunosuppression, diabetes, recent surgery, or prosthetic implants as risk enhancers.
🦠 Common Organisms
- Staphylococcus aureus (MSSA/MRSA) – most frequent in adults.
- Streptococci (Groups A & B) – adults & neonates.
- Neisseria gonorrhoeae – sexually active young adults, often migratory polyarthritis.
- Gram-negatives (E. coli, Pseudomonas) – elderly, immunocompromised, indwelling catheters.
- Fungi / Mycobacteria – immunosuppressed or endemic exposures.
👶 Paediatric Risk – Kocher’s Criteria
- Fever >38.5°C 🌡️
- Non–weight-bearing on affected limb 🚶♂️❌
- ESR >40 mm/hr or CRP >20 mg/L
- WCC >12 × 10⁹/L
Risk of septic arthritis: 0 factors = 2%, 1 factor = 20%, 2 factors = 40%, 3 factors = 73%, 4 factors = 93%.
🔎 Synovial Fluid Analysis
| Condition | Appearance | WBC /mm³ | PMN % |
|---|
| Normal | Clear | <200 | <25% |
| Inflammatory (RA, gout) | Yellow, cloudy | 2,000–100,000 | >50% |
| Septic | Opaque, pus-like | >50,000 | >75% |
| Gonococcal | Cloudy | 34,000–68,000 | >75% |
🧾 Initial Management (NICE-aligned)
- Immediate joint aspiration 💉 – send for Gram stain, culture, and crystals.
- Blood tests: FBC, ESR/CRP, blood cultures.
- Imaging: X-ray baseline; MRI for deep-seated infection or prosthetic evaluation.
- Empirical IV antibiotics – adjust once cultures available:
- Native joint: IV Flucloxacillin 2 g QDS (first-line for MSSA).
- MRSA risk: add Vancomycin or Teicoplanin.
- Gram-negative / immunosuppressed: add Gentamicin or Ciprofloxacin.
- Gonococcal: IV Ceftriaxone (1 g daily) ± switch to oral therapy once improved.
- Prosthetic joint infection: urgent orthopaedic review, consider DAIR (debridement, antibiotics, implant retention) or revision surgery.
- Drainage: repeated aspiration, arthroscopic washout, or open surgery (hip especially).
- Duration: Typically 2 weeks IV → 4 weeks oral (total ~6 weeks), adjust by organism & clinical response.
- Pain & mobility: NSAIDs for symptom control; early mobilisation once inflammation improves.
- Monitor for sepsis: vital signs, organ function, fluid balance.
🚨 Red Flags – Escalate Immediately
- Prosthetic joint infection
- Hip or shoulder involvement (difficult aspiration, rapid cartilage destruction)
- Immunocompromised patients (steroids, DM, HIV, transplant)
- Systemic sepsis or haemodynamic instability
- Delayed presentation (>24–48 hrs) → higher risk of joint destruction
💡 Student Tips
- Monoarthritis in an adult = septic until proven otherwise.
- Always send synovial fluid for culture **before antibiotics** unless patient unstable.
- Polyarticular involvement is usually **haematogenous spread** or immunocompromised state.
- Use Kocher criteria in children to guide urgency of orthopaedic referral.
- Monitor CRP trends to assess treatment response.
References
