Septic Arthritis

Septic arthritis is a joint emergency — untreated, it causes irreversible cartilage destruction within 24–48 hours. The Kocher criteria (fever >38.5°C, non-weight-bearing, ESR >40, WBC >12) predict likelihood. Joint aspiration before antibiotics is…

BSH / BHPR Septic Arthritis Guideline

The pathway

1 · Apply Kocher criteria

Fever >38.5°C (+1)
Non-weight-bearing (+1)
ESR >40 mm/hr (+1)
WBC >12 ×10⁹/L (+1)
Predicted probability: 4 criteria = 99.6%
Also check CRP (>20 mg/L suggestive) and serum uric acid (to distinguish gout)

2 · Joint aspiration before antibiotics

Aspirate under sterile conditions (ultrasound-guided for hip)
Send fluid for: Gram stain + MC&S, crystal analysis (exclude gout/pseudogout), WBC with differential
Synovial WBC >50,000/μL with >75% PMNs highly suggestive of infection
Do NOT delay aspiration awaiting imaging

3 · IV antibiotics after aspiration

Start within 1 hour of clinical diagnosis, after aspiration
Empirical: IV flucloxacillin 2g QDS (Staph aureus most common)
MRSA risk (prosthetic joint, healthcare exposure, previous MRSA): IV vancomycin 15–20mg/kg BD
Sexually active young adult: IV ceftriaxone 1g OD for gonococcal cover
Sickle cell disease: add cover for Salmonella

4 · Joint washout within 24 hours

Arthroscopic washout preferred (knee, shoulder, ankle)
Open washout for hip, or if arthroscopy fails
Repeat washout if inadequate drainage or failure to improve at 48–72h
Leave drain in situ post-washout if purulent

5 · Monitor response

Daily joint assessment: warmth, effusion, range of movement
CRP and WBC every 48–72h — should trend down
Repeat aspiration if clinical deterioration or CRP rising
Orthopaedic review daily while inpatient

6 · IV-to-oral step-down and duration

Total antibiotic duration: 4–6 weeks
IV minimum 2 weeks, then step down to oral when clinically improving and CRP falling
Oral step-down: flucloxacillin 1g QDS or clindamycin 300mg QDS (penicillin intolerant)
Physiotherapy from day 2 to prevent contracture and stiffness

Drugs

Drug	Dose	Route	Notes
Flucloxacillin	2g IV QDS	IV then PO	Empirical first-line (Staph aureus cover). Step-down to 1g PO QDS once clinically improving and CRP falling.
Vancomycin	15–20mg/kg BD	IV	For MRSA risk or prosthetic joint infection. Monitor AUC/MIC or trough levels. Target AUC 400–600 mg·h/L.
Ceftriaxone	1g OD	IV	For gonococcal arthritis in sexually active young adults. Review and rationalise when sensitivities available.
Clindamycin	300mg QDS	PO	Oral step-down in penicillin-intolerant patients. Excellent bone and joint penetration.

When to escalate

Hip septic arthritis — same-day surgical joint washout regardless of time of day,Failure to improve by 48–72 hours — repeat washout, broaden antibiotics, repeat cultures,Septic shock secondary to septic arthritis — ITU, vasopressors, surgical washout under anaesthesia,Prosthetic joint infection — orthopaedic consultant, consider DAIR (debridement, antibiotics, implant retention) versus implant removal,Gonococcal arthritis not responding to ceftriaxone — GUM referral, partner notification, screen for concurrent STIs

Reference: BSH / BHPR Guidelines for Management of the Hot Swollen Joint 2006 / NICE Evidence Review 2021

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