title: Validation of a new radiographic measurement of acetabular version: the transverse axis distance (TAD).
abstract: OBJECTIVE
  This study has three aims: (1) validate a new radiographic measure of acetabular version, the transverse axis distance (TAD) by showing equivalent TAD accuracy in predicting CT equatorial acetabular version when compared to a previously validated, but more cumbersome, radiographic measure, the p/a ratio; (2) establish predictive equations of CT acetabular version from TAD; (3) calculate a sensitive and specific cut point for predicting excessive CT acetabular anteversion using TAD.
  
  
  METHODS
  A 14-month retrospective review was performed of patients who had undergone a dedicated MSK CT pelvis study and who also had a technically adequate AP pelvis radiograph. Two trained observers measured the radiographic p/a ratio, TAD, and CT acetabular equatorial version for 110 hips on a PACS workstation. Mixed model analysis was used to find prediction equations, and ROC analysis was used to evaluate the diagnostic accuracy of p/a ratio and TAD.
  
  
  RESULTS
  CT equatorial acetabular version can accurately be predicted from either p/a ratio (p < 0.001) or TAD (p < 0.001). The diagnostic accuracies of p/a ratio and TAD are comparable (p =0.46). Patients whose TAD is higher than 17 mm may have excessive acetabular anteversion. For that cutpoint, the sensitivity of TAD is 0.73, with specificity of 0.82.
  
  
  CONCLUSIONS
  TAD is an accurate radiographic predictor of CT acetabular anteversion and provides an easy-to-use and intuitive point-of-care assessment of acetabular version in patients with hip pain.
authors.affiliation: Division of Musculoskeletal Radiology, Department of Radiology, University of Colorado School of Medicine, University of Colorado Denver, Aurora, CO, USA.
authors.forename: Ashley
authors.initials: A
authors.lastname: Nitschke
authors.affiliation: Department of Biostatistics and Informatics, Colorado School of Public Health, University of Colorado, Aurora, CO, USA.
authors.forename: Jeffery R
authors.initials: JR
authors.lastname: Lambert
authors.affiliation: Department of Biostatistics and Informatics, Colorado School of Public Health, University of Colorado, Aurora, CO, USA.|Department of Radiology, University of Colorado School of Medicine, University of Colorado Denver, Aurora, CO, USA.
authors.forename: Deborah H
authors.initials: DH
authors.lastname: Glueck
authors.affiliation: Division of Musculoskeletal Radiology, Department of Radiology and Orthopaedics, University of Colorado School of Medicine, University of Colorado Denver, Aurora, CO, USA.
authors.forename: Mary Kristen
authors.initials: MK
authors.lastname: Jesse
authors.affiliation: Division of Sports Medicine and Hip Preservation, Department of Orthopaedics, University of Colorado School of Medicine, University of Colorado Denver, Aurora, CO, USA.
authors.forename: Omer
authors.initials: O
authors.lastname: Mei-Dan
authors.affiliation: Division of Musculoskeletal Radiology, Department of Radiology and Orthopaedics, University of Colorado School of Medicine, University of Colorado Denver, Aurora, CO, USA.
authors.forename: Colin
authors.initials: C
authors.lastname: Strickland
authors.affiliation: Division of Musculoskeletal Radiology, Department of Radiology and Orthopaedics, University of Colorado School of Medicine, University of Colorado Denver, Aurora, CO, USA. bdpetersen@inlandimaging.com.|Division of Musculoskeletal Radiology, Inland Imaging, 801 S Stevens, Spokane, 99204, WA, USA. bdpetersen@inlandimaging.com.
authors.forename: Brian
authors.initials: B
authors.lastname: Petersen
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging*; D000293:Adolescent; D000328:Adult; D005260:Female; D006618:Hip Dislocation, Congenital / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed; D055815:Young Adult
keywords: Acetabular anteversion; Acetabular version; Hip; Radiographic assessment; Transverse axis distance