Dynamic femoral head coverage following periacetabular osteotomy for developmental dysplasia of the hip

Background: Developmental dysplasia of the hip reduces hip stability due to insufficient femoral head coverage. Periacetabular osteotomy surgery aims to increase this coverage. Typically measured using radiographs, most coverage assessments are limited to static hip positions and cannot capture 3D anatomy. This study quantified how dynamic 3D femoral coverage changes during gait and squat after periacetabular osteotomy surgery and compared dynamic coverage to static measures. Methods: Pre- and post-surgery CT scans from 38 patients with hip dysplasia were used to reconstruct 3D femur and pelvis bones with which gait and squat were simulated. Models of 38 control subjects were also created. The femoral head was divided into anteromedial, anterolateral, posteromedial, and posterolateral regions. Regional coverage was compared pre- and post-surgery, and against controls, in a static neutral position, during the stance phase of gait, and throughout the squat cycle. Findings: Lateral coverage increased post-surgery in the static neutral position (anterolateral: 4.9 ± 3.6 % to 13.8 ± 5.6 %; posterolateral: 22.9 ± 15.4 % to 39.8 ± 15.2 % (p ≤ 0.001)) and throughout gait and squat (p ≤ 0.001). Average changes in neutral anterolateral coverage (+8.9 ± 4.5 %) were similar to average changes during gait (+8.1 ± 3.0 %), but not squat (+12.0 ± 1.9 %). Static neutral coverage post-surgery differed significantly from dynamic coverage in every region of the femoral head during all of gait, and most of squat. Interpretation: While static measures follow some patterns of dynamic coverage after surgery, they miss important variations that can impact joint loading. Understanding how periacetabular osteotomy changes dynamic femoral head coverage can aid with operative planning and assessment to optimize outcomes during daily activities.