Several measurements are used to evaluate hip dysplasia in hip ultrasound of children. Despite having being used since the 1980s, reliability studies have failed to find acceptable reliaiblity values for the gold standard ultrasound methods.

This study will evaluate three ultrasound measurement methodologies in a high quality controlled setting, to investigate the best achieveable reliability and agreement of the investigated measurements used in hip dysplasia diagnostics.

In DDH diagnostics, measurements of acetabular alpha angles and femoral head coverages (FHC), developed by Graf and Harcke/Terjesen respectively, have been gold standard since the 1980s. Despite their widespread use, the reliability of these measurements has been questioned due to the relative complexity of acquiring the necessary corIDrect frontal 2D plane or "standard plane". In the only meta-analysis of the reliability of ultrasound (US) metrics in dysplasia, the interrater reliability of the alpha angles was mediocre while the reliability of the FHC was poor. Critics of these findings however argue that the low reliability reported in studies are due to misinterpretation and misapplication of the Graf method.

The pubo-femoral distance (PFD) was proposed in 2013 as a new measurement for assessing DDH, while the reliability is reportedly higher than the gold standard US methods, it has never been directly compared to these.

This study aims to evaluate the inter- and intrarater reliability of Graf's alpha and beta angles, the FHC and PFD in children referred for hip US in a selective ultrasound screening program for DDH.

Inclusion Criteria:

• Children referred to the radiological outpatient at AUH for hip ultrasound examination, suspect of DDH.
• Children receiving follow-up ultrasound for previously diagnosed DDH

Exclusion Criteria:

• Children deemed too agitated to participate in hip US with double measurements by two radiologists.

Study protocol, analysis plan, and analytic code will be available upon written request to the first author.

After study has been published (expected end 2024)

upon written request to the first author.

The radiologist will be blinded to each others measurements, until all examinations have been performed.