Influence of patient axial malpositioning on the trueness and precision of pelvic parameters obtained from 3D reconstructions based on biplanar radiographs

Radiographs are often performed to assess pelvic and hip parameters, but results depend upon correct pelvis positioning. Three-dimensional (3D) reconstruction from biplanar-radiographs should provide parameters that are less sensitive to pelvic orientation, but this remained to be evaluated. Computerized-tomographic scans of six patients were used both as a reference and for generating simulated frontal and lateral radiographs. These simulated radiographs were generated while introducing axial rotations of the pelvis ranging from 0A degrees to 20A degrees. Simulated biplanar-radiographs were utilized by four operators, three times each, to perform pelvic 3D-reconstructions. These reconstructions were used to assess the trueness, precision and global uncertainty of radiological pelvic and hip parameters for each position. In the neutral position, global uncertainty ranged between +/- 2A degrees for pelvic tilt and +/- 9A degrees for acetabular posterior sector angle and was mainly related to precision errors (ranging from 1.5A degrees to 7A degrees). With increasing axial rotation, global uncertainty increased and ranged between +/- 5A degrees for pelvic tilt and +/- 11A degrees for pelvic incidence, sacral slope and acetabular anterior sector angle, mainly due to precision errors. Radiological parameters obtained from 3D-reconstructions, based on biplanar-radiographs, are less sensitive to axial rotation compared to plain radiographs. However, the axial rotation should nonetheless not exceed 10A degrees. Pelvic radiological parameters could be affected by patient malpositioning. Biplanar radiograph-based 3D reconstructions were performed at increments of axial rotation. Trueness, precision and global uncertainty were evaluated for pelvic and hip radiological parameters. Hip parameters were less affected by rotation compared to pelvic parameters. Maintaining the pelvis close to the neutral position is recommended to ensure the highest possible accuracy.