Pediatric Bone and Joint Infections

Epidemiology and Pathogenesis

The American Academy of Pediatrics notes that osteomyelitis with concurrent septic arthritis occurs in over 50% of pediatric bone and joint infection cases, particularly in children under 18 months of age where transphyseal vessels allow direct spread between bone and joint 1, 2
Staphylococcus aureus is the predominant pathogen across all pediatric age groups, responsible for the majority of acute hematogenous osteomyelitis cases 1
Kingella kingae is also a common pathogen in children under 4 years of age and should be considered 1, 2
Half of all pediatric osteomyelitis cases occur in children <5 years of age, making this the highest-risk population 3, 1

The American College of Radiology recommends that radiographs of both lower extremities should be obtained first, though they are often normal in acute osteomyelitis as bone changes require 10-14 days to become visible 6, 1, 7
Radiographs have low sensitivity for early osteomyelitis, with bone destruction not visible until >30% osseous matrix destruction has occurred 6
MRI is the diagnostic modality of choice with 82-100% sensitivity for osteomyelitis and septic arthritis 6, 3, 1
Contrast-enhanced MRI improves detection of infection in unossified growth cartilage (chondritis) in children <6 years, where cartilage commonly appears normal on unenhanced sequences 6

The American Academy of Pediatrics notes that septic arthritis is an orthopedic emergency requiring urgent diagnosis and treatment to prevent permanent joint damage 2, 7
Delayed diagnosis results in premature physeal arrest or permanent joint damage, making prompt recognition essential despite the fact that the classic triad of fever, pain, and diminished mobility occurs in only ~50% of cases 1