Acute Pelvic Osteomyelitis in Children

BACKGROUND: Pelvic acute hematogenous osteomyelitis (PAHO) is an uncommon pediatric infection often presenting with nonspecific symptoms, resulting in delayed diagnosis. Data on its clinical presentation, microbiology, management and outcomes remain limited. METHODS: A retrospective single-center study included children diagnosed with pelvic AHO at Meyer Children's Hospital IRCCS (Florence, Italy) between January 2016 and December 2025. Patients were stratified into isolated osteomyelitis and osteomyelitis with septic arthritis. RESULTS: Thirty-seven children were included, representing 16% of all AHO cases during the study period. Median age was 8.9 years (interquartile range [IQR] 4.1-12.1); 70% were male. The ilium was most frequently involved. Sixteen patients (43.2%) had concomitant septic arthritis and were significantly older than those with isolated osteomyelitis (P = 0.019). Isolated osteomyelitis was associated with longer time to diagnosis (median 8 days, IQR 6-14) versus septic arthritis (median 5 days, IQR 4-8.5; P = 0.025). Concomitant pyomyositis was identified in 67.5% of cases. A pathogen was isolated in 43.2% of patients, most commonly methicillin-susceptible Staphylococcus aureus. Median intravenous antibiotic duration was 17 days, total antibiotic duration 45 days. Treatment failure occurred in 16.2%, chronic complications in 5.4%. CONCLUSIONS: PAHO encompasses 2 distinct clinical phenotypes, isolated osteomyelitis and osteomyelitis with septic arthritis, differing in age at presentation, inflammatory response, and diagnostic delay. Magnetic resonance imaging is essential for defining disease extent, identifying associated pyomyositis, and guiding management.