Ultrasound (US) is the primary imaging modality for detecting acetabular dysplasia and/or hip dislocation in early infancy because until 4 to 6 months of age, the femoral head is primarily cartilaginous, limiting the utility of plain radiographs to visualize key structures until ossification begins at around the 4 month mark. The primary metric used for evaluating developmental dysplasia of the hip (DDH) by US is the acetabular alpha angle.
Quader et al. (2018) performed a systematic review and meta-analysis of the variability of dysplasia metrics between repeated measurements for the assessment of the infant hip. They found high variability and low agreement in all reported dysplasia metrics. Furthermore, they report that the last 3 decades, the repeatability of dysplasia metrics has not markedly improved and may even have declined, indicating a genuine need for improving repeatability and reliability of ultrasound-based DDH diagnosis.