Geometric Transformation Algorithm for Acetabular Cup Orientation: Converting 2D Radiographic Projections to 3D Spatial Positioning

BACKGROUND/AIM: Hip replacement is one of the most common and successful surgeries of our time. However, with increasing numbers of total hip arthroplasties, postoperative complications due to inadequate cup positioning are rising. Accurate measurement of acetabular cup inclination and anteversion is critical for optimal outcomes. While various measurement systems exist, they often require additional hardware, specialized training, or lack integration across the care continuum. This study aims to develop and validate software for automated measurement of acetabular cup positioning, comparing its performance to standard CAD measurements. MATERIALS AND METHODS: The geometric basis for analyzing the acetabular cup is that a hemisphere in 2D projection forms an ellipse, described by a conic section equation. We developed a Python-based software utilizing computer vision techniques for edge detection and ellipse fitting to determine anteversion and inclination from standard radiographs. The software was trained and validated using X-ray images of a pelvic phantom with a conventional acetabular cup (Allofit, Zimmer Biomet) at various predefined angles. CAD software (MediCAD) served as the validation standard. The intraclass correlation coefficient (ICC) quantified agreement between methods. RESULTS: