A 3D Femoral Head Coverage Metric for Enhanced Reliability in Diagnosing Hip Dysplasia

Abstract

Developmental dysplasia of the hip (DDH) in infancy refers to hip joint abnormalities ranging from mild acetabular dysplasia to irreducible femoral head dislocations. While 2D B-mode ultrasound (US) is currently used clinically to estimate the severity of femoral head subluxation in infant hips, such estimates suffer from high inter-exam variability. We propose using a novel 3D US-derived dysplasia metric, the 3D femoral head coverage (\(FHC_{3D}\)), which characterizes the 3D morphology of the femoral head relative to the vertical cortex of the ilium in an infants hip joint. We compute our 3D dysplasia metric by segmenting the femoral head using a voxel-wise probability map based on a tomographic reconstruction of 2D cross-sections each labeled with a probability score of that slice containing the femoral head. Using a dataset of 20 patient hip examinations, we demonstrate that our reconstructed femoral heads agree reasonably well with manually segmented femoral heads (mean dice coefficient of 0.71), with a significant reduction in variability of the associated metric relative to the existing manual 2D-based FHC ratio (\({\sim } 20\%\) reduction, \(p<0.05\)). Our findings suggest that the proposed 3D dysplasia metric may be more reliable than the conventional 2D metric, which may lead to a more reproducible test for diagnosing DDH.