Diagnostic errors in the echography of the hip in newborns

Neonatal hip sonography according to Graf employs a standardized image in a frontal section plane ("3-point system") and a good scanner adjustment (the femoral head must be anechoic, like the hyaline cartilage roof triangle). Pathologic conditions can change some of these parameters. The authors examined 6,000 neonatal hips in order to point out the commonest causes of diagnostic error. Two types of error were considered: method errors and interpretation errors. Method errors: they are due to the choice of transducer and frequency, to scanner adjustment and definition of the standard section plane. Their incidence was 2.25% and supported by an uncorrect definition of the standard section plane. Interpretation errors: they come from the wrong localization of some reference points--i.e., lower iliac margin, labrum--, uncorrect evaluation of increased echogenicity of the cartilaginous roof, infant age, application of radiographic criteria and uncorrect measurements of alpha and beta angles. Interpretation errors had 5.5% incidence; they were all due to the uncorrect measurement of alpha (3.18%) and beta (2.33%) angles, especially in pathological hips (68%). To reduce the number of errors, the authors suggest to strictly apply Graf's method, to make a diagnosis based on the morphological changes of the cartilaginous and osseous acetabular roof and, only later on, to measure alpha and beta angles to confirm the diagnosis or in the follow-up.