TP4.2 Beyond 2D Radiographs: Prospective Quantitative 3D CT Assessment of Femoral Head Coverage Influences Planning of Periacetabular Osteotomy in Developmental Dysplasia of the Hip

Abstract Background Assessment of femoral head coverage in developmental dysplasia of the hip (DDH) is traditionally based on two-dimensional (2D) radiographic measurements. However, these measurements incompletely represent the complex three-dimensional morphology of dysplastic hips and may lead to variability in diagnostic interpretation. Quantitative three-dimensional imaging may improve diagnostic accuracy and surgical planning. We developed a quantitative 3D CT-based method (Q3DCT) to provide detailed evaluation of femoral head coverage. Methods In this prospective observational study, ten consecutive patients with symptomatic DDH scheduled for periacetabular osteotomy underwent Q3DCT-based femoral head coverage analysis alongside conventional radiographic measurements including the lateral centre-edge angle (LCEA), Sharp angle, and Tönnis angle. Radiographs obtained during two separate outpatient visits were used to evaluate measurement reproducibility. CT-based 3D reconstruction enabled quadrant-specific coverage assessment relative to the femoral head centre and was incorporated into preoperative planning of periacetabular osteotomy. Reliability of conventional and Q3DCT measurements was assessed by three independent observers using intraclass correlation coefficients (ICC). The treating surgeon evaluated the clinical value of Q3DCT for surgical planning using a visual analogue scale (VAS). Results Median total femoral head coverage was 54% (IQR 52–60%). Q3DCT demonstrated excellent reliability for total coverage (ICC 0.96) and across all quadrants (ICC 0.89–0.99). Conventional radiographic measurements showed good same-visit reliability (ICC 0.84–0.90), but reliability decreased substantially when compared across separate outpatient visits (ICC 0.25–0.84), highlighting their sensitivity to acquisition variability. Q3DCT was rated highly valuable for surgical planning (median VAS 8/10) and influenced the planned correction strategy in 9 of 10 patients. Conclusion Q3DCT enables highly reliable and spatially detailed evaluation of femoral head coverage in DDH and frequently influences preoperative planning. The marked decrease in reliability of conventional radiographic measurements across visits highlights an important limitation of 2D imaging in this setting. As a feasibility study, larger prospective validation is warranted; however, Q3DCT represents a promising adjunct for precise, personalised surgical planning in hip preservation.