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

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.