Aim The presentation of acute onset of limp in a child creates a diagnostic challenge for the clinician. The purpose of this study was to identify distinguishing features specific to septic arthritis and so aid the clinician in ruling out the diagnosis without painful and expensive investigation.
Methods We retrospectively reviewed all cases of children who were evaluated at a district general hospital between 1996 and 2010 presenting with acute limp unrelated to trauma. Cases were divided into two diagnostic groups: septic arthritis and non-septic arthritis. Diagnoses were defined on the basis of the joint fluid white cell count (WCC), the results of cultures of joint fluid and blood, and the clinical course. Univarate analysis was performed to evaluate the predictive value of previously identified factors in determining septic arthritis: Fever (>38.5°C); weight bearing status, WCC >12.0, erythrocyte sedimentation rate (ESR) >40, C reactive protein (CRP) >20.
Results Our records search identified 148 potential cases. 14 cases fulfilled the diagnostic criteria for septic arthritis of the 99 included in the study. Comparing septic arthritis versus non-septic arthritis: Sex distribution M: F (71% vs 69%); Mean age (6.1 vs 6.4 years). Differences between the groups were noted in the duration of symptoms (2.1 vs 5.9 days). Patients who had septic arthritis differed significantly (p<0.001) from non-septic arthritis patients with regard to: non-weight bearing status (86% vs 24%); presence of fever in the history (93% vs 28%); ESR (mean 136.9 vs 12.9); CRP (mean 98.1 vs 10.8) and WCC (mean 19.2 vs 9.5).
Conclusion Distinguishing between transient synovitis and septic arthritis is essential as the management and potential complications are very different. Our study provides strong support for the use of non-weight bearing status, fever (>37.5°C), WCC >12.0, ESR >40, CRP >20 in the differentiation of the conditions. Using our data and comparing it with published data we propose that it is unnecessary to perform further investigation for septic arthritis in patients who have all three of: ESR value <40, WCC <12 and CRP value <20.