Practice Question of the Day: MSK/Orthopedics

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A 10-year-old boy presents to the emergency department with fever, refusal to bear weight on his right leg, and localized tenderness over the distal femur. His parents report that he had a minor scrape on his knee one week ago. No reported trauma. On examination, his temperature is 38.9°C (102°F), and his right distal femur is warm, swollen, and tender to palpation. Laboratory tests show:

  • WBC: 14,500/mm³
  • ESR: 82 mm/hr
  • CRP: 12.5 mg/dL

An X-ray of the femur is ordered below.

What is the most appropriate next step in management?

A. Obtain a bone biopsy
B. MRI of the affected limb
C. Empiric IV antibiotics and repeat X-ray in 2 weeks
D. Observation and supportive care

Answer is below

Answer:

B. MRI of the affected limb

Explanation:

This patient presents with fever, localized bone pain, elevated inflammatory markers, and refusal to bear weight, which is highly suggestive of acute hematogenous osteomyelitis. Since early X-rays are often normal, MRI is the most sensitive test for early osteomyelitis and should be performed to confirm the diagnosis.

  • Bone biopsy (A) is typically done if there is diagnostic uncertainty or failure to respond to empiric antibiotics.
  • Empiric IV antibiotics and repeat X-ray in 2 weeks (C) may delay treatment in a high-suspicion case; MRI is needed to confirm early changes.
  • Observation and supportive care (D) is inappropriate, as untreated osteomyelitis can lead to septic arthritis, bone destruction, and chronic infection.

PACE The PANCE Pearls:

  • Staphylococcus aureus is the most common cause of osteomyelitis in children.
  • Salmonella is associated with sickle cell disease.
  • MRI is the best early imaging study; X-rays may not show changes for 7-14 days.
  • Empiric IV antibiotics (e.g., nafcillin, cefazolin, or vancomycin) should be started after obtaining blood cultures.

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