Sonographic acetabular rim irregularities in infants - can they be identified and measured?

Hip ultrasonography according to Graf is the standard screening method for developmental dysplasia of the hip (DDH). While acetabular roof morphology is well described, irregularities of the bony acetabular rim have not been systematically evaluated. We describe a previously unreported finding termed sonographic acetabular rim irregularity (SARI). We asked (1) whether SARI can be reliably identified by independent examiners and (2) whether its size can be measured reproducibly. In this matched-control study, standardized hip sonograms of 96 infants with a presumed SARI and 104 matched infants not suspicious of irregularities of the bony acetabular rim were analyzed. Two examiners with different experience levels independently assessed the presence of SARI and performed relative size measurements of a SARI. Inter- and intra-observer agreement was evaluated using Cohen's kappa, and a receiver operating characteristic analysis was performed. Inter-observer agreement was substantial (κ = 0.65108), and intra-observer agreement was substantial too (κ = 0.73519). Mean relative SARI size was from 0.20290 to 0.21687 for the two examiners, with no significant differences in the measurement of the SARI between the two examiners. A cutoff value of 0.1667 enabled reliable identification of a SARI. SARI is a reproducibly identifiable and measurable sonographic finding in infant hips. This method provides a basis for future studies evaluating its clinical relevance. LEVEL OF EVIDENCE: Level III, matched-control study.