Pain for Greater Than 4 Days Is Highly Predictive of Concomitant Osteomyelitis in Children With Septic Arthritis

Background: There is no evidence-based consensus on the risk factors for concomitant osteomyelitis and septic arthritis. The purpose of this study was to investigate clinical parameters predictive of concomitant osteomyelitis in children with septic arthritis. Methods: A retrospective review was conducted on patients with septic arthritis with magnetic resonance imaging (MRI) between January 2004 and October 2016 at a tertiary care pediatric hospital. Medical charts were reviewed for information including symptoms, diagnosis of osteomyelitis, serum laboratory studies, joint fluid analyses, imaging results, and treatment. Positive diagnosis of osteomyelitis was defined as a hyperintense signal of osseous structures on T2-weighted MRI consistent with infection per attending pediatric radiologist final read. Results: A total of 71 patients with 73 septic joints were included. The mean age was 6 +/- 4 (0.1 to 17) years and the mean follow-up was 14.9 +/- 24.1 (1.0 to 133.1) months. Septic arthritis with concomitant osteomyelitis occurred in 43 of 71 (61%) patients, whereas 28 of 71 (39%) patients had septic arthritis alone. Inflammatory markers such as white blood cell count, erythrocyte sedimentation rate, and C-reactive protein on admission were not associated with concomitant osteomyelitis. Multivariate logistic regression revealed that positive joint fluid bacterial culture (P=0.021) and pain for >4 days before admission (P=0.004) are independent risk factors for concomitant osteomyelitis in children with septic arthritis. Among the 24 septic arthritis patients with pain for >4 days before presentation, 96% (23/24) had concomitant osteomyelitis, whereas 43% (20/47) of patients with pain for <= 4 days had concomitant osteomyelitis. Conclusion: Pain for >4 days before presentation is an independent predictor of osteomyelitis in children with septic arthritis. In pediatric septic arthritis, MRI should be considered, particularly in patients presenting with pain for >4 days as 96% of these patients had concomitant osteomyelitis.