Classic measures of hip dysplasia do not correlate with three-dimensional computer tomographic measures and indices.

UNLABELLED: Acetabular dysplasia is a precursor to osteoarthritis of the hip, and it causes acute and degenerative injuries of soft tissue stabilizers. Traditional radiographic assessments of dysplasia are useful in moderate and severe dysplasia, but they have questionable reliability in mild dysplasia. Computed tomography (CT) reconstruction provides a method for calculation of acetabular geometry and analysis of existing radiographic methods. We performed a retrospective radiographic review of anteroposterior pelvic films and their corresponding pelvic CT scans. Using 30 skeletally mature patients, we analyzed the following five measurements for 60 hips: lateral centre edge angle of Wiberg (LCE), Tönnis angle, Sharp angle, a modified Sharp angle, and the depth to width acetabular index. We also estimated hip surface areas, volumes, and ratios from 3-D reconstructions of a CT scan taken within 60 days of the plain radiograph. The Pearson Correlation Coefficient was used to evaluate the relationship between the plain film measurements and the computed hip indices. No moderate or strong correlation was found between the measured plain film indices and the calculated hip indices. Traditional 2-D measurements used to define acetabular dysplasia have little to no ability to quantify hip volumes and surface areas. CT reconstruction provides a better screening tool in the identification of subtle acetabular hip dysplasia in adults.

LEVEL OF EVIDENCE: Level III.