549 Hip Int ( 2011 ; : 05 ) 549 - 558 21 Classic measures of hip dysplasia do not correlate with three-dimensional computer tomographic measures and indices Allston J. Stubbs 1 , Adam W. Anz 1 , John Frino 1 , Jason E. Lang 1 , Ashley A. Weaver 2 , Joel D. Stitzel 2 1 Department of Orthopaedic Surgery, Wake Forest Baptist Health, Winston Salem, NC - USA 2 Department of Biomedical Engineering, Wake Forest University Health Sciences, Winston Salem, NC - USA ABSTRACT: Acetabular dysplasia is a precursor to osteoarthritis of the hip, and it causes acute and degenerative injuries of soft tissue stabilisers. Traditional radiographic assessments of dysplasia are useful in moderate and severe dysplasia, but they have questionable reliability in mild dysplasia. Com- puted 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 correspond- ing 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 calcu- lated 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 KEY WORDS: Dysplasia, CT reconstruction, Measure, Three-dimensional Accepted: August 02, 2011 ORIGINAL ARTICLE DOI: 10.5301/HIP.2011.8696 INTRODUCTION Acetabular dysplasia is an abnormality involving the inclina- tion, version, and/or volume of the acetabulum. The dys- plastic acetabulum concentrates a greater amount of hip joint reactive force upon a smaller surface area producing early degenerative hip disease through focal cartilage wear (1-4). Whereas marked dysplasia is easily identified radio- graphically, subtle dysplasia is more difficult to identify. Due to advances in hip arthroscopy, clinicians have begun to recognise a spectrum of disease often involving mild dys- plasia and femoroacetabular impingement. Analysis of sub- tle morphologic abnormalities is now of greater concern, as they place a greater burden on the secondary soft tissue stabilasers of the hip (labrum, capsule and ligaments) mak- ing them more prone to shear or compressive injury (4). As a consequence, adults with mild dysplasia who are at risk of damage to labral and capsular tissue are of interest (4),