Primary Cause of Osteomyelitis in Children
Staphylococcus aureus is the predominant pathogen responsible for the majority of acute hematogenous osteomyelitis cases across all pediatric age groups. 1, 2, 3
Microbiology by Age Group
The causative organisms vary by age, requiring age-specific consideration:
- Staphylococcus aureus remains the most common etiologic agent overall, accounting for approximately 45% of culture-positive cases 4, 5
- Neonates (<1 month): Group B streptococcus must be considered alongside S. aureus 1
- Children <4 years: Kingella kingae is increasingly recognized as a common pathogen and should be specifically sought 1, 3
- Patients with sickle cell disease: Salmonella species are disproportionately represented 1
- Methicillin-resistant S. aureus (MRSA): Increasing prevalence from 6% to 31% over recent years, associated with worse clinical outcomes including higher inflammatory markers, longer hospital stays, and increased complication rates 5
Pathophysiology of Hematogenous Spread
Hematogenous bacterial seeding is the most common mechanism of infection in children. 2
The metaphysis serves as the primary infection site due to specific vascular anatomy:
- Looping nutrient vessels slow blood flow in the metaphyseal region without crossing the growth plate, creating an ideal environment for bacterial adherence and proliferation 1
- In children ≤18 months, transphyseal vessels allow direct spread from metaphysis to epiphysis and adjacent joint space, explaining why >50% of pediatric cases have concurrent septic arthritis 1, 3
- In older children (>18 months), the physis typically acts as a barrier preventing epiphyseal spread 1
Age-Related Distribution
- Half of all pediatric osteomyelitis cases occur in children <5 years of age, making this the highest-risk population 1, 3
- Children <2 years are more likely to develop septic arthritis than isolated osteomyelitis due to transphyseal vessel anatomy 2, 3
- Children aged 2-10 years have slightly more osteomyelitis than septic arthritis 2
Critical Clinical Pitfall
The classic triad of fever, pain, and diminished mobility occurs in only ~50% of cases, making delayed diagnosis common 1, 3. This delay can result in premature physeal arrest or permanent joint damage, emphasizing the need for high clinical suspicion even with atypical presentations 3.