Kocher criteria calculator: septic arthritis of the hip
In a child with an irritable hip, count four findings: a history of fever above 38.5 °C (101.3 °F), refusal to bear weight, ESR of 40 mm/h or more, and a serum white cell count over 12,000/mm³. In Kocher's 1999 study the chance of septic arthritis rather than transient synovitis was under 0.2% with none, 3.0% with one, 40.0% with two, 93.1% with three and 99.6% with all four.
Clinical disclaimer
When to use the Kocher criteria calculator
- Child with acute atraumatic hip pain or limp.
- Use alongside labs, imaging, and orthopedic evaluation.
- Not validated for other joints or postoperative hips.
How the Kocher criteria score works
The Kocher criteria give one point each for four findings: a history of fever above 38.5 °C (101.3 °F), non–weight bearing on the affected side, ESR of at least 40 mm/hr, and a serum white blood cell count over 12,000/mm³ (12 ×10⁹/L). The total is 0 to 4.
- Predicted probability of septic arthritis (Kocher 1999): under 0.2% with 0 predictors, 3.0% with 1, 40.0% with 2, 93.1% with 3 and 99.6% with 4.
- Kocher's 2004 prospective validation found the same four predictors; the rule performed less well in the new population (ROC area 0.86 vs 0.96).
- Caird 2006 measured fever orally (over 38.5 °C) and added C-reactive protein over 2.0 mg/dL as a fifth predictor. That five-item variant is not scored here.
- Young children with Kingella kingae infection often meet 2 or fewer Kocher criteria (71% in Yagupsky 2014, as reviewed by Valisena 2024 below), so a low score is less reassuring under about 4 years.
Clinical use & interpretation
The Kocher score is designed to support, not replace, clinical reasoning. It is most useful when combined with a careful history, focused physical exam, and appropriate lab and imaging studies.
- Low scores with a well-appearing child and preserved weight bearing may support conservative management and close follow‑up.
- Intermediate scores should prompt low‑threshold consultation with orthopedics and imaging to distinguish septic arthritis from transient synovitis and other causes of limp.
- High scores (3–4) merit urgent orthopedic input, imaging, and consideration of hip aspiration, even while additional diagnostics are being arranged.
Remember that early septic arthritis can present with incomplete criteria and that partially treated infections or immunocompromised children may not follow classic patterns. Persistent non–weight bearing or systemic illness should drive management more than the numeric score alone.
Common pitfalls and escalation triggers
- Over-relying on a low score early in illness despite worsening exam or persistent non–weight bearing.
- Delaying orthopedic discussion when multiple criteria are present and imaging access is limited.
- Applying hip-derived thresholds directly to other joints without joint-specific pathways.
- Missing partially treated infection patterns with blunted fever or lab responses.
Differential diagnosis & red flags
A child with an acutely painful hip may have conditions other than septic arthritis, and some of those diagnoses also require urgent attention. Use Kocher scoring as a starting point while keeping a broad differential in mind.
- Consider transient synovitis, osteomyelitis, trauma, slipped capital femoral epiphysis (SCFE), Legg–Calvé–Perthes disease, and malignancy.
- Red flags include systemic toxicity, severe pain at rest, inability to bear weight, night pain, and laboratory evidence of significant inflammation or sepsis.
- Abnormal imaging (e.g., effusion on ultrasound, bone changes on X‑ray or MRI) should be interpreted together with the Kocher score and the clinical picture.
Documentation checklist
- Weight-bearing status and hip exam findings.
- Vitals, fever history, and lab values (ESR/CRP, WBC).
- Imaging results and orthopedic consult timing.
- Score band, differential diagnosis, and follow-up plan.
Related calculators & guides
Frequently asked questions
The Kocher criteria estimate the probability that a child with an acutely painful hip has septic arthritis rather than a benign condition such as transient synovitis. The score sums four findings: non–weight bearing, a history of fever above 38.5 °C (101.3 °F), ESR of at least 40 mm/hr, and a serum white cell count over 12,000/mm³.
One point each for a history of fever above 38.5 °C (101.3 °F), non–weight bearing on the affected side, ESR of at least 40 mm/hr, and a serum white cell count over 12,000/mm³ (12 ×10⁹/L), as defined by Kocher in 1999 and validated in 2004.
Use the score to frame your risk assessment and guide discussions about imaging and joint aspiration, not to make decisions in isolation. Children with higher scores are more likely to need urgent orthopedic input, imaging, and possibly hip aspiration, but clinical judgment and local pathways remain critical.
No. Kocher used ESR. Caird 2006 added C-reactive protein over 2.0 mg/dL as a fifth, separate predictor (and measured fever orally, over 38.5 °C). This calculator scores the original four items; follow your institution’s preferred variant.
A very low score lowers the probability of septic arthritis but does not eliminate it, especially early in the course or in partially treated cases. Persistently non–weight bearing children, or those who appear ill, warrant close observation and often imaging or consultation even when the numeric score is low.
Escalate when the score is high, when the child appears toxic or systemically unwell, or when pain and non–weight bearing persist despite analgesia. Many pathways recommend urgent orthopedic consultation and imaging when multiple Kocher criteria are present.
The Kocher criteria were derived for the pediatric hip. Use caution applying them to knees or other joints; follow joint-specific pathways.
It can be harder to assess weight bearing and pain localization in toddlers. Use caregiver observations, exam, and imaging with a lower threshold for consultation.
Do not delay escalation when clinical concern is high. Use available findings, obtain urgent consultation, and complete missing data as soon as feasible.
Repeat focused scoring and functional assessment whenever symptoms evolve and at defined observation intervals. Serial trend plus clinical appearance is safer than a one-time score.
Include timed Kocher variables, repeat exam trajectory, current imaging status, and the exact specialist decision needed. This shortens handoff delay and improves action clarity.
References
- 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(12):1662-1670.
- Kocher MS, Mandiga R, Zurakowski D, et al. Validation of a clinical prediction rule for the differentiation between septic arthritis and transient synovitis of the hip in children. J Bone Joint Surg Am. 2004;86(8):1629-1635.
- Valisena S, De Marco G, Vazquez O, et al. The Kocher–Caird criteria for pediatric septic arthritis of the hip: time for a change in the Kingella era? Microorganisms. 2024;12(3):550. (Tabulates Kocher 1999/2004 fever as temperature ≥ 38.5 °C.)
- Caird MS, Flynn JM, Leung YL, et al. Factors distinguishing septic arthritis from transient synovitis of the hip in children: a prospective study. J Bone Joint Surg Am. 2006;88(6):1251-1257.