Reliability of 2D and 3D ultrasound for infant hip dysplasia in the hands of novice users

Abstract

Purpose: Developmental dysplasia of the hip (DDH) diagnosis by two-dimensional ultrasound (2DUS) can have poor inter-rater reliability. 3D ultrasound (3DUS) may be more reliably performed, particularly by novice users. We compared intra- and inter-rater reliability between expert and novice operators performing 2DUS and 3DUS for DDH.

Materials and methods: Infants with suspected DDH were assessed with 2DUS and 3DUS. Novice operators had 1.5 h of training and Experts had 5-15 years' experience. Images included two 2DUS static and two 3DUS sweep images per operator. Image quality was assessed by 5-point system (yes/no: full femoral head; full acetabular roof; horizontal iliac wing; os ischium; absent motion/artifact). 2DUS indices (alpha angle, coverage) were measured centrally by a blinded reader with 2 years DDH US experience. 3DUS was post-processed by semi-automated custom software generating acetabular surface models, indices and estimated probability of DDH. Gold-standard diagnosis of each hip as normal, borderline or dysplastic was based on radiologist review of expert 2DUS.

Results: Thirty infants, mean age 10.8 weeks were enrolled. Quality scores were 2.7±1.2 Novice versus 4.9±0.3 Expert for 2DUS (p = 0.04), and 4.2±1.0 Novice versus 4.9±0.3 Expert for 3DUS (p = 0.99). Inter-rater reliability was poor for 2DUS (ICC=0.10 for alpha angle, 0.04 for acetabular coverage) and moderate to high for 3DUS (ICC=0.73-0.83 for alpha angle, 0.55 for acetabular coverage). Intra-rater reliability and diagnostic accuracy was higher for 3DUS than 2DUS.

Conclusion: Novice operators can perform 3DUS for DDH with reliability and accuracy approaching expert sonographers. Novices perform 2DUS with poor reliability and accuracy.

Key points: • Novice/expert inter-rater reliability improved from poor with 2DUS to moderate/high with 3DUS. • Novice operators using 3DUS correctly classified 57/58 (98%) of infant hips. • DDH can be reliably assessed by novice operators using 3DUS.

Keywords: Diagnostic imaging; Hip dislocation, congenital; Observer variation; Reproducibility of results; Ultrasonography.