Abstract
Background:Although differentiating between transient synovitis and septic hip arthritis is challenging, clinical prediction rules such as the Kocher criteria (KC) have been shown to help with the diagnosis of septic hip arthritis in children. Their performance in septic arthritis due to less virulent pathogens such as Kingella Kingae, however is unknown. We aimed to describe the performance of these clinical prediction rules in pre-school children with septic hip arthritis due to different pathogens. We hypothesised that the number of KC or modified KC met would be lower in children with septic hip arthritis caused by K. kingae, compared to those caused by Staphylococcus aureus. Methods:In this retrospective multicentre study conducted in Australia and New Zealand between 2012-2016, we included children with confirmed septic hip arthritis due to S. aureus (n=29), K. kingae (n=20), other pathogens (n=32), and no pathogen identified (n=48). We applied the KC (temperature, weight-bearing, erythrocyte sedimentation rate, white blood cell count) and the modified KC (C-reactive protein added) and assessed their sensitivity for septic hip arthritis, using cut offs of KC & GE; 3 and modified KC & GE; 4. Results:The score of the KC and the modified KC was not lower in K. kingae compared to S. aureus (P=0.27, P=0.21). In addition, both the sensitivity for the KC (S. aureus 18/29 (62.1%); K. kingae 12/20 (60.0%)), and for the modified KC (S. aureus 18/29 (62.1%); K. kingae 12/20 (60.0%)) did not differ between K. kingae and S. aureus. Of all children with septic hip arthritis, the sensitivity of both the KC and modified KC were 56.6% (95%CI 47.6-65.3). Conclusions:The clinical prediction rules had comparable performance in K. kingae infections to those caused by S. aureus. Concerningly, less than 60% of the children with confirmed septic hip arthritis met the cut-off values. These prediction rules lack sensitivity to rule-out septic hip arthritis in the early assessment of pre-school aged children with acute hip pain.