The four Kocher criteria (and CRP)
Score one point for each criterion present. CRP is not part of the original Kocher score, but it is the strongest single predictor (Caird 2006) and is used alongside the score.
| Criterion | Positive if |
|---|---|
| Non-weight-bearing | Refuses or cannot bear weight on the leg |
| Fever | Over 38.5 °C (101.3 °F), by history or in the department |
| ESR | Over 40 mm/h |
| Serum WBC | Over 12,000/mm³ |
| CRP (added, not scored) | Over 2 mg/dL (20 mg/L) |
- If ESR or WBC was not done, the score may be underestimated.
Probability of septic arthritis by Kocher score
These are the predicted probabilities from the original derivation (Kocher 1999).
| Kocher score | Predicted probability of septic arthritis |
|---|---|
| 0 | Under 0.2% |
| 1 | 3% |
| 2 | 40% |
| 3 | 93% |
| 4 | 99.6% |
How the score and CRP guide the next step
High risk: a score of 3 or 4, or a score of 2 with CRP over 2 mg/dL. Septic arthritis is likely. Involve orthopedics now for ultrasound-guided aspiration and washout if pus is found; the septic hip is a surgical emergency. Joint fluid WBC over 50,000/mm³ with neutrophils supports septic arthritis. Get MRI if osteomyelitis or pyomyositis is suspected, as both are common in children.
Intermediate risk: a score of 2, or a score of 1 with CRP over 2 mg/dL. The hip cannot be safely sorted by exam alone. Do a hip ultrasound and aspirate any effusion with orthopedics. Consider MRI if there is no effusion but pain persists. Hold antibiotics until aspiration if the child is stable.
Low risk: other combinations. Transient synovitis is likely; treat symptoms and recheck. A CRP of 2 mg/dL or less lowers concern.
In Lyme-endemic areas, Lyme arthritis can mimic septic arthritis, so send Lyme serology.
Antibiotics for septic arthritis of the hip (PIDS/IDSA 2023)
Start antibiotics after aspiration. Do not delay aspiration for antibiotics unless the child is septic. Take a blood culture before antibiotics, and send joint fluid for Gram stain, culture (inoculate a blood culture bottle) and Kingella PCR.
| Drug | Dose | When to use |
|---|---|---|
| Cefazolin IV | 33–50 mg/kg every 8 h (100–150 mg/kg/day), max 2 g per dose | Where MRSA is uncommon (under 10–20%); covers Kingella (common under 4 years) |
| Clindamycin IV | 13 mg/kg every 8 h (40 mg/kg/day), max 900 mg per dose | MRSA common and clindamycin resistance under 10%; does not cover Kingella |
| Vancomycin IV | 15 mg/kg every 6–8 h, dose by levels or AUC | MRSA with clindamycin resistance, or severely ill; add cefazolin under 4 years for Kingella |
| Cephalexin PO | 25–37.5 mg/kg every 6–8 h (75–150 mg/kg/day), max 4 g/day | Oral step-down for MSSA and Kingella |
- Switch to oral once afebrile, improving and CRP falling.
- Total course usually 10–14 days for uncomplicated septic arthritis.
Managing likely transient synovitis
Give ibuprofen 10 mg/kg (max 400 mg) by mouth every 6 to 8 hours with food. Transient synovitis usually settles in 3 to 10 days.
- Recheck in 24 to 48 hours; return for fever, worsening pain or refusal to walk.
- Symptoms over 7 to 10 days or recurrence: X-ray (Perthes disease, or SCFE in older children) and review.
- Always examine the knee and the whole limb, because hip pain can refer to the knee.
Use the free tool
Kocher criteria with CRP, next steps, and septic arthritis antibiotics by weight.
Open Septic Hip vs Transient Synovitis →Common questions
What are the 4 Kocher criteria?
Inability to bear weight, fever over 38.5 °C (101.3 °F), ESR over 40 mm/h, and serum WBC over 12,000/mm³. One point each, for a score of 0 to 4.
What does a Kocher score of 2 mean?
A predicted probability of septic arthritis of 40%. On its own it is intermediate risk: do a hip ultrasound and aspirate any effusion. With CRP over 2 mg/dL it is treated as high risk, with urgent aspiration and orthopedics.
Why add CRP to the Kocher criteria?
CRP over 2 mg/dL (20 mg/L) is not part of the original score but was the strongest single predictor in Caird 2006. A raised CRP increases concern at any score, and a CRP of 2 mg/dL or less lowers it.
Which antibiotic covers Kingella kingae?
Cefazolin and cephalexin cover Kingella, which is common under 4 years. Clindamycin and vancomycin do not, so add cefazolin to vancomycin in children under 4.
Sources
Kocher MS, Zurakowski D, Kasser JR. Differentiating between septic arthritis and transient synovitis of the hip in children: an evidence-based clinical prediction algorithm. J Bone Joint Surg Am 1999;81:1662–1670. Caird MS, et al. Factors distinguishing septic arthritis from transient synovitis of the hip in children. J Bone Joint Surg Am 2006;88:1251–1257. Woods CR, Bradley JS, Chatterjee A, et al. Clinical practice guideline by PIDS and IDSA: 2023 guideline on diagnosis and management of acute bacterial arthritis in pediatrics. J Pediatric Infect Dis Soc 2024;13(1):1–59.
For education only, not medical advice. Always confirm against current guidelines and your local protocols. Pedemy is independent and not affiliated with or endorsed by the organizations cited.