A 15-month-old child is evaluated because he is not using his right arm. Parents report when they picked him up the prior evening from his child-care center, he was not using his right arm and seemed uncomfortable. They asked the provider of his small, in-home child-care center if anything happened. She said no, but she had noticed him crying around lunchtime. He has been walking since 1 year of age, and the parents report that he falls a lot. After stopping breastfeeding at 1 year of age, he has been refusing all milk and dairy products and prefers to drink water or juice. He does not take supplemental vitamins and always has sunscreen on when outside. On examination, he holds his arm close to his body and has point tenderness along the shaft of the humerus. He winces when the arm is moved. The remainder of the examination results are within normal limits. An X-ray of the arm shows an oblique fracture of the right humerus.

Which of the following is the most likely explanation for this child’s fracture?

  1. Accidental injury
  2. Non-accidental trauma
  3. Osteogenesis imperfecta
  4. Rickets

Let me think about this step by step:

  1. First, let's analyze the key information presented:

    • 15-month-old with acute onset of not using right arm
    • No clear history of trauma reported by daycare
    • Developmental history: walking since 12 months, falls frequently
    • Dietary history: refuses milk/dairy since 12 months, no vitamin supplements
    • Always wears sunscreen outside
    • Physical exam shows point tenderness and pain with movement
    • X-ray confirms oblique fracture of humerus

  2. Let's consider each option:

    Osteogenesis imperfecta:

    • Would typically have multiple fractures
    • Often has family history
    • Usually presents earlier
    • No mention of blue sclera or other typical features

    Accidental injury:

    • Common in toddlers
    • However, there should usually be a clear history of trauma
    • Caregivers usually witness or can describe the incident

    Non-accidental trauma:

    • Several red flags present:
      • No clear history of injury
      • Delay in seeking care
      • Vague explanation from caregiver
      • Type of fracture (oblique) is concerning
      • Age group is typical for abuse

    Rickets:

    • Risk factors present:
      • No milk intake
      • Always wearing sunscreen
      • No vitamin supplementation
    • However:
      • Single acute fracture is not typical
      • No mention of other rickets signs
      • Would expect more gradual onset

  3. Conclusion: The most likely explanation is non-accidental trauma because:

    • The combination of no clear history, delay in seeking care, vague explanation from caregiver, and type of fracture are classic red flags
    • The age group (15 months) is in the highest risk period for physical abuse
    • While the child has risk factors for rickets, the presentation is more consistent with trauma
    • Single oblique fracture without clear trauma history is more consistent with inflicted injury than accident or metabolic bone disease
Claude 3.5 Sonnet

Claude 3.5 Sonnet is the only model that consistently answers this question correctly. Most other models tested, including GPT-4o, o1-preview, and o1-mini, incorrectly choose rickets. Gemini 1.5 Pro will sometimes choose non-accidental injury and other times choose accidental injury.

This type of question is particularly valuable because it mimics real clinical scenarios where:
  • Not all information points to the same conclusion
  • Some findings may be misleading
  • The correct diagnosis requires integrating social and historical factors, not just physical findings

Most models tested focus too much on laboratory-style memorized associations (no milk = rickets) and miss the significance of the social aspects (vague history, daycare setting). They also appear to not recognize classic abuse patterns (unexplained injury + inconsistent history).

Back to Archive