title: Comparison of six radiographic projections to assess femoral head/neck asphericity.
abstract: Early radiographic detection of femoroacetabular impingement might prevent initiation and progression of osteoarthritis. The structural abnormality in femoral-induced femoroacetabular impingement (cam type) is frequently asphericity at the anterosuperior head/neck contour. To determine which of six radiographic projections (anteroposterior, Dunn, Dunn/45 degrees flexion, cross-table/15 degrees internal rotation, cross-table/neutral rotation, and cross-table/15 degrees external rotation) best identifies femoral head/neck asphericity, we studied 21 desiccated femurs; 11 with an aspherical femoral head/neck contour and 10 with a spherical femoral head/neck contour. To radiographically quantify femoral head asphericity, we measured the angle where the femoral head/neck leaves sphericity (angle alpha). The aspherical femoral head/neck contours had a greater maximum angle alpha (70 degrees ) compared with the spherical head/neck contours (50 degrees ). The angle alpha varied depending on the radiographic projection: it was greatest in the Dunn view with 45 degrees hip flexion (71 degrees +/- 10 degrees ) and least in the cross-table view in 15 degrees external rotation (51 degrees +/- 7 degrees ). Diagnosis of a pathologic femoral head/neck contour depends on the radiologic projection. The Dunn view in 45 degrees or 90 degrees flexion or a cross-table projection in internal rotation best show femoral head/neck asphericity, whereas anteroposterior or externally rotated cross-table views are likely to miss asphericity.
  
  
  METHODS
  Prognostic study, level II-1 (retrospective study).
authors.affiliation: Department of Orthopaedic Surgery, Balgrist University Hospital, Zurich, Switzerland. dominikmeyer@bluewin.ch
authors.forename: Dominik C
authors.initials: DC
authors.lastname: Meyer
authors.forename: Martin
authors.initials: M
authors.lastname: Beck
authors.forename: Tom
authors.initials: T
authors.lastname: Ellis
authors.forename: Reinhold
authors.initials: R
authors.lastname: Ganz
authors.forename: Michael
authors.initials: M
authors.lastname: Leunig
mesh_terms: D005260:Female; D005270:Femur Head / Q000000981:diagnostic imaging*; D005272:Femur Neck / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D011859:Radiography / Q000379:methods