Background: The aim of this study was to improve knowledge of pediatric pyogenic sacroiliitis (PSI) in the pediatric population based on a consecutive case series.

Method: We conducted a single-center cross-sectional study on 16 patients admitted to the emergency department of our Hospital between January 1990 and December 2015 with a confirmed diagnosis of PSI. The patients were divided into 2 groups by age: infants (6 months to 4 years) and children–adolescents (4–16 years). The features of PSI, clinical signs and symptoms, laboratory tests, bacteriologic investigations, radiologic examinations and outcome were compared among the 2 groups.

Results: Patients in the children–adolescent group usually presented with a history of limping and buttock or lower back pain, and methicillin-susceptible Staphylococcus aureus was the most frequent pathogen. We observed a second peak of incidence of PSI in infants with consistent difference in clinical and microbiologic presentation. Infants were more likely to have an ambiguous onset with the refusal to bear weight as the only consistent clinical manifestations, and biologic investigations demonstrated higher erythrocyte sedimentation rate and platelet counts. However, all blood and joint fluid cultures were sterile in the infant group.

Conclusion: PSI in infants and adolescents may represent 2 different conditions. Although PSI is mainly caused by S. aureus in the children–adolescent group, clinical manifestations and biologic characteristics of PSI in infants suggest Kingella kingae as the etiology osteoarticular infection. Thus, oropharyngeal swab polymerase chain reaction assay for K. kingae and magnetic resonance imaging should be considered for early diagnosis and treatment of this condition in the younger age group.