Comparison of six radiographic projections to assess femoral head/neck asphericity.
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).
Meyer
Dominik C
DC
Department of Orthopaedic Surgery, Balgrist University Hospital, Zurich, Switzerland. dominikmeyer@bluewin.ch
Beck
Martin
M
Ellis
Tom
T
Ganz
Reinhold
R
Leunig
Michael
M
D005260:Female; D005270:Femur Head / Q000000981:diagnostic imaging*; D005272:Femur Neck / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D011859:Radiography / Q000379:methods