Study objective: To determine the diagnostic value of screening laboratory and initial body temperature data in differentiating septic arthritis of the hip from transient synovitis of the hip in children who present to the emergency department with a complaint of hip pain. Design: Retrospective review of cases of septic arthritis of the hip and transient synovitis of the hip in a 1:2.5 ratio. Setting: An urban regional children's hospital with 20,000 annual ED visits. Results: Ninety-four children with transient synovitis of the hip and 38 children with septic arthritis of the hip were identified. The children with septic arthritis of the hip had a significantly higher initial temperature (38.1 C versus 37.2 C, P = .000014), mean erythrocyte sedimentation rate (44 mm/hr versus 19 mm/hr, P = .000001), and mean WBC count (13,200/mm3 versus 11,200/mM3. P = .02). However, the degree of overlap in these variables was large. The combination of an erythrocyte sedimentation rate of more than 20 mm/hr and/or a temperature of more than 37.5 C identified 97% of all cases of septic arthritis of the hip. Conclusion: There is clinically significant overlap in the erythrocyte sedimentation rate, temperature, and WBC count in children with septic arthritis of the hip versus transient synovitis of the hip. All children with an irritable hip without a clearly identified source who have an erythrocyte sedimentation rate of more than 20 mm/hr or a temperature of more than 37.5 C should be considered for diagnostic hip aspiration.
