• Kwang-Soon Song, Kirti Ramnani, Byung-Woo Min, Ki Cheor Bae, Chul-Hyun Cho, and Kyung-Jae Lee.
• Department of Orthopaedic Surgery, Keimyung University, Daegu, Korea. skspos@dsmc.or.kr
• J Pediatr Orthop. 2011 Sep 1;31(6):644-7.

BackgroundA pathognomonic finding of slipped capital femoral epiphysis (SCFE) is a combination of the decrease in the height of the slipped epiphysis and the position of external rotation and flexion of hip. We believe that decrease in the acetabulotrochanteric distance (ATD) on an anteroposterior (AP) radiograph represents this finding.Material And MethodsIn a retrospective study of 25 consecutive cases of unilateral SCFE, we defined ATD as the distance between a line connecting the superolateral margins of the acetabulae with a second line, parallel to the first line, which goes through the tip of the greater trochanter on each hip and acetabulotrochanteric angle (ATA) as the angle between a line connecting the superolateral margins of the acetabulae with a second line connecting the tip of greater trochanter on each side. The difference in ATD and ATA between both hips in each case was evaluated and their correlation was determined using the Pearson correlation coefficient.ResultsNineteen cases (76%) showed difference in ATD of > 2 mm and positive ATA divergence of >1 degree. The average difference in ATD was 6.6 mm (range, 0 to 25 mm); the average ATA divergence was 2.4 degree (range, 0 to 5.3 degree).ConclusionsOur findings show that the difference in acetabulotrochanteric distance (ATD) between hips is an easy, reliable, and sensitive finding present on an AP radiograph of patients with unilateral SCFE. ATD should be taken into consideration while evaluating AP radiographs of a patient suspected to have SCFE, and further evaluation with lateral hip radiographs should be carried out to confirm the diagnosis.Level Of EvidenceLevel IV.

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