Kocher criteria calculator for septic arthritis
Use this Kocher criteria calculator to estimate septic arthritis risk in a child with an inflamed hip, then pair the score with exam trajectory, labs, imaging, and orthopedic input.
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 assign one point each for four findings: non–weight bearing on the affected side, fever > 38.5°C, ESR > 40 mm/hr (or CRP > 2 mg/dL in some variants), and WBC > 12 ×10⁹/L. The total score ranges from 0 to 4.
- Approximate probabilities from the original Kocher study: 0 points ≈ 0.2%, 1 point ≈ 3%, 2 points ≈ 40%, 3 points ≈ 93%, 4 points ≈ 99% likelihood of septic arthritis.
- Our implementation reflects these bands and displays the approximate probability label alongside the total score.
- Later work suggests CRP may refine the model; this calculator notes that refinement while implementing the original 4‑item score.
Bedside workflow for septic hip evaluation
- Confirm atraumatic painful hip presentation and complete focused exam with weight-bearing assessment.
- Obtain fever history and baseline inflammatory markers (ESR/CRP, WBC) promptly.
- Calculate Kocher score, but interpret alongside overall toxicity, age context, and symptom evolution.
- Use score band to guide urgency of imaging, orthopedic consultation, and aspiration planning.
- Reassess early if trajectory worsens or remains non–weight bearing despite initial low/intermediate score.
Reassessment cadence
- After initial score and analgesia: repeat focused exam and weight-bearing assessment in the same care block.
- If intermediate risk or uncertain diagnosis: continue serial reassessment while imaging/consultation proceeds.
- Any worsening pain, fever, or functional decline: immediate reassessment and escalation.
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.
Immediate escalation triggers
- Persistent inability to bear weight despite initial low or intermediate score.
- Toxic appearance, worsening pain at rest, or rapid inflammatory marker rise.
- Imaging/lab discordance that leaves septic arthritis unresolved.
- Limited access to urgent reassessment in a child with evolving symptoms.
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.
Handoff template
- Kocher components with exact values and score band.
- Current weight-bearing status and focused hip exam trajectory.
- Imaging obtained/pending and orthopedic consult status.
- Differential diagnosis and rationale for current management path.
- Explicit reassessment interval and escalation trigger.
Escalation packet for orthopedic review
- Exact Kocher variables with timestamps (fever, WBC, ESR/CRP, weight-bearing status).
- Current clinical trajectory including analgesia response and repeat exam findings.
- Imaging status (US/X-ray/MRI) and unresolved diagnostic questions.
- Differential ranking and reason septic arthritis remains likely or uncertain.
- Immediate decision needed from orthopedic team (aspiration timing, OR pathway, continued observation).
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, fever, elevated ESR/CRP, and elevated WBC.
The classic Kocher criteria give one point each for non–weight bearing on the affected side, fever above 38.5°C, ESR above 40 mm/hr, and WBC above 12 ×10⁹/L. Some modern pathways also review CRP alongside the original four findings.
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.
Original Kocher criteria used ESR, but later studies have incorporated CRP as an alternative or additional marker. This calculator implements the classic four-item score and notes CRP refinement; you should 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.