Transient synovitis and the irritable hip — branching viva

Branching framework

Open with the one-sentence problem representation. This is a well-looking child in the peak age group with an acute post-viral limp, and transient synovitis is the likely diagnosis once septic arthritis has been excluded. State the principle aloud — transient synovitis is a diagnosis of exclusion, made only after the Kocher criteria and the inflammatory markers have lowered the probability of pus — before you discuss anything else. The examiner is listening for whether you reach for the score and the markers before you reach for the reassurance. ^{[1] [3]}

Apply the Kocher criteria to exclude sepsis. The four predictors are a fever above 38.5 degrees, an inability to bear weight, an ESR above 40, and a white cell count above 12,000, with the Caird addition of a CRP above 20 milligrams per litre. State the rising probability with each predictor — below one per cent with none, forty per cent with two, ninety-three per cent with three — and be ready for the calibration probe, because the Caird prospective study found the original Kocher probabilities may overestimate. The child with zero or one predictor and a well appearance fits transient synovitis, while two or more predictors demand aspiration. ^{[1] [3]}

Branch to the single most important investigation. Ultrasound is the first-line investigation, confirming the hip effusion and guiding an aspiration when one is needed. State that the markers frame the probability and that the ultrasound confirms the effusion, and be ready to explain that a normal ultrasound does not exclude early septic arthritis. If the examiner probes a culture-negative effusion in the under-four, name Kingella kingae and the blood-culture-bottle inoculation and the polymerase chain reaction, because the young child with a culture-negative effusion is not safely reassured. ^{[6] [9]}