This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.
A limping child with a painful hip
When a child suddenly limps or refuses to walk because of hip pain, the most likely cause is transient synovitis, a harmless inflammation that settles in a few days. The dangerous alternative is septic arthritis, a bacterial infection of the joint that can destroy it within days. The two can look alike at first, and the Kocher criteria help doctors decide which children need an urgent joint aspiration.
The four criteria
In 1999, Mininder Kocher and colleagues at Boston Children’s Hospital found four independent predictors of septic arthritis:
- Inability to bear weight on the affected leg
- Fever above 38.5 °C (101.3 °F)
- Erythrocyte sedimentation rate (ESR) above 40 mm/h
- White blood cell count above 12,000 per mm³
Probability of septic arthritis
| Criteria present | Probability (1999 study) |
|---|---|
| 0 | under 0.2% |
| 1 | 3% |
| 2 | 40% |
| 3 | 93.1% |
| 4 | 99.6% |
Example
A five-year-old who refuses to stand on the left leg and has a temperature of 39 °C, with an ESR of 25 mm/h and a white count of 10,000, meets 2 criteria: an intermediate probability of about 40%. Such a child needs further tests, usually an ultrasound to look for fluid in the joint and often an aspiration.
Validation and C-reactive protein
When the same team tested the criteria in a new group of children, the probabilities were lower: about 93% with four criteria, 73% with three and 35% with two. Other centers found weaker results still, because their patients were different. A C-reactive protein above 2.0 mg/dL (20 mg/L) was later added as a fifth predictor by Caird and colleagues, and a normal CRP makes septic arthritis less likely.
Use with care
The criteria apply to children with an acutely painful hip, not to other joints, newborns or children already on antibiotics. They support clinical judgment and do not replace it. Lyme arthritis, osteomyelitis, Perthes disease, a slipped capital femoral epiphysis and fractures can also cause a limp, so any child with fever and a limp, or a limp that does not improve, should be seen promptly.