Quantifying Dynamic Assessment of Developmental Dysplasia of the Hip

Although physical and ultrasound (US)-based screening for congenital deformities of the hip (developmental dysplasia of the hip, or DDH) is routinely performed in most countries, one of the most commonly performed maneuvers done under ultrasound observation - dynamic assessment - has been shown to be relatively unreliable and is associated with significant misdiagnosis rates, on the order of 29%.Our overall research objective is to develop a quantitative method of assessing hip instability, which we hope will standardize diagnosis across different raters and health-centers, and may perhaps improve reliability of diagnosis. To quantify dynamic assessment, we propose to use the variability in femoral head coverage (FHC) measurements within multiple US scans collected during a dynamic assessment. In every US scan, we use our recently-developed automatic FHC measuring tool which leverages phase symmetry features to approximate vertical cortex of ilium and a random forest classifier to identify approximate location of the femoral head. Having estimated FHC in each scan, we estimate the change in FHC across all the US scans during a dynamic assessment and compare this change with variability of FHC found in previous studies.Our findings - in a dynamic assessment on an infant done by an orthopaedic surgeon, the femoral centre moved by up to 19% of its diameter during distraction, from 55% FHC to 74% FHC. This change in FHC is slightly greater than its variability in static US scans reported in previous studies, suggesting that the distraction force likely produced a real lateral displacement. Our clinician’s qualitative assessment concluded the hip to be normal as this degree of distraction was not indicative of instability. This suggests that our technique likely has sufficient resolution and repeatability to quantify differences in laxity between stable and unstable hips, although this presumption will have to be confirmed in a subsequent study with additional subjects. The long-term significance of this approach to evaluating dynamic assessments may lie in increasing early diagnostic sensitivity in order to prevent dysplasia remaining undetected prior to manifesting itself in early adulthood joint disease.