Regarding acute hematogenous osteomyelitis in children, all of the following statements are correct EXCEPT:

## Acute Hematogenous Osteomyelitis in Children — Pathology & Microbiology ### Anatomical Site of Infection **Key Point:** The metaphyseal region (not epiphysis) is the primary site of infection in acute hematogenous osteomyelitis in children. The metaphysis is preferred because: - Capillary loops in the metaphyseal vessels are wide and tortuous, causing blood flow to slow - This sluggish circulation allows bacteria to settle and proliferate - The metaphysis is highly vascular and has minimal phagocytic activity **Important distinction:** The growth plate (physis) acts as a barrier and prevents spread from metaphysis to epiphysis in young children. In infants <1 year and adolescents >12 years, the growth plate is more permeable and epiphyseal involvement is more common. ### Causative Organisms | Organism | Frequency | Notes | | --- | --- | --- | | *Staphylococcus aureus* | >80% | Most common; includes MRSA strains | | *Streptococcus pyogenes* | 5–10% | Group A Strep | | *Haemophilus influenzae* | <5% | Rare post-vaccination | | *Gram-negative rods* | <5% | Neonates, immunocompromised | **High-Yield:** *S. aureus* is the overwhelming pathogen in all age groups and all anatomical sites. ### Blood Culture Positivity **Clinical Pearl:** Blood cultures are positive in only 40–60% of acute hematogenous osteomyelitis cases, NOT >90%. This is a common misconception. - Cultures should still be obtained before starting antibiotics to guide targeted therapy - Negative blood cultures do not exclude osteomyelitis - Bone biopsy/aspiration culture is more reliable (>90% sensitivity) **High-Yield:** Always obtain blood cultures, but do not delay antibiotic therapy while awaiting results. ### Why Option 3 Is Wrong The statement claims infection begins in the epiphysis and spreads across the growth plate — this is **backwards**. In children: 1. Infection begins in the **metaphysis** (sluggish blood flow) 2. The growth plate acts as a barrier and prevents spread to the epiphysis in most cases 3. Epiphyseal involvement occurs only when the growth plate is permeable (infants, adolescents) or when the infection is very severe [cite:Robbins 10e Ch 26]