Septic Arthritis in Infants Younger Than 3 Months: A Retrospective Review.

Septic arthritis in infants is rare and can be difficult to diagnose. This study reviewed a series of patients younger than 3 months to identify factors that may assist in early diagnosis and treatment. A query of records at a large Midwestern pediatric hospital (1994-2010) was performed to identify all patients younger than 3 months at the time of diagnosis. Analysis included birth history, joint involvement, physical examination findings, laboratory results, imaging results, method of treatment, and outcome. In 14 cases (11 boys, 3 girls; mean age at diagnosis, 42.2 days), complete records were available for review. Involved joints included the knee, hip, and shoulder. The most common findings on physical examination were decreased range of motion (100%), tenderness (100%), and swelling (71.4%). Mean temperature was 38.5°C. Mean white blood cell count was 18.5 K/µL, mean erythrocyte sedimentation rate was 48.9 mm/h, and mean C-reactive protein level was 6.1 mg/dL. More than half (57.1%) of joint aspirates grew positive cultures, and 41.7% of blood cultures had positive results. Causative organisms were group B streptococcus, methicillin-sensitive Staphylococcus aureus, Haemophilus influenzae, Streptococcus pneumoniae, Salmonella enterica, and Candida albicans. The most common physical examination findings in infants younger than 3 months with septic arthritis include tenderness, decreased range of motion, and swelling. White blood cell count, C-reactive protein level, and erythrocyte sedimentation rate are likely to be elevated, but these findings should be used in combination with findings on physical examination and radiographic studies to aid in diagnosis.