Kocher Criteria Calculator — Septic Arthritis vs Transient Synovitis of the Hip
Apply the Kocher criteria to a child with an irritable hip — non-weight-bearing, fever over 38.5 °C, ESR over 40 mm/h and WBC over 12,000 — and see the predicted probability of septic arthritis.
How it works
One point each: non-weight-bearing · fever > 38.5 °C · ESR > 40 mm/h · WBC > 12,000 cells/mm³. Predicted probability of septic arthritis (Kocher 1999): 0 → < 0.2% · 1 → 3.0% · 2 → 40.0% · 3 → 93.1% · 4 → 99.6%.
The Kocher criteria (Kocher, Zurakowski and Kasser, Journal of Bone and Joint Surgery 1999) were derived in children presenting with an acutely irritable hip to separate septic arthritis, a surgical emergency, from the much more common transient synovitis. Four independent predictors were identified; the probability of septic arthritis rose steeply with the number present. Later validation cohorts found lower probabilities than the original study, and Caird and colleagues (2006) added a C-reactive protein above 2.0 mg/dL as a fifth predictor. The criteria support but do not replace clinical judgement, ultrasound and joint aspiration.
Worked example
A 6-year-old will not bear weight on the left leg and has had a fever of 38.9 °C, with an ESR of 32 mm/h and a white cell count of 10,500/mm³: 2 of 4 Kocher criteria are met, which carried a 40.0% predicted probability of septic arthritis in the derivation study — intermediate probability, so aspiration and further tests should be considered.
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: a prospective study. J Bone Joint Surg Am 2006
Frequently asked questions
What are the four Kocher criteria?
Inability to bear weight on the affected side, fever above 38.5 °C, an erythrocyte sedimentation rate above 40 mm/h and a white blood cell count above 12,000 cells/mm³.
How accurate are the Kocher criteria?
In the 1999 derivation study the probability of septic arthritis was 93.1% with three criteria and 99.6% with four. Validation studies in other hospitals found lower figures, so the criteria are best used to guide, not replace, imaging and joint aspiration.
What is the modified Kocher (Caird) rule?
Caird and colleagues added C-reactive protein above 2.0 mg/dL (20 mg/L) as a fifth predictor. A raised CRP is a strong independent predictor of septic arthritis.
What is transient synovitis?
A self-limiting inflammation of the hip lining, usually after a viral illness, in children aged about 3–10. It causes a limp and hip pain but usually settles within a week with rest and anti-inflammatory medicine.
Related calculators
Clinical decision tool for education and for use by trained clinicians alongside clinical judgement — not a diagnosis and not a substitute for medical assessment. Scores and cut-offs come from the cited validation studies and may not apply to every patient; follow local protocols.