title: Experimental study of an original radiographic view for diagnosis of cam-type anterior femoroacetabular impingement.
abstract: OBJECTIVE
  Primary paraclinical investigation to look for femoral morphological abnormality consistent with cam-type anterior femoroacetabular impingement (FAI) must include specific radiographic projections of the hip from the following: cross-table, frog-leg or Dunn (90° and 45° flexion). We use a frog-leg type view with fixed angles as described by Chiron, obtained with the patient in a supine position, with the hip in 45° flexion-abduction and 30° external rotation. The X-ray beam is anteroposterior and centred on the femoral head. We evaluated this view by comparing it with other views in common use.
  
  
  METHODS
  In this experimental study, we created artificial radio-opaque morphological abnormalities secured onto normal femoral necks. The femurs were placed in relation to a fixed pelvis using orthogonal landmarks, in the positions of the various radiographic views. The digital radiographs were analysed by two observers. Nineteen femurs were included to reveal a difference of 5° between the alpha angle of Nötzli et al. [11] measured on the Dunn view and the frog-leg 45/45/30 view (Student's paired test).
  
  
  RESULTS
  The highest mean values of the alpha angle of Nötzli were always obtained with the frog-leg 45/45/30 view (87.4°, 86.2°, 84.5°) and the lowest with the cross-table view. We found a mean difference of 8.95° with the 90° Dunn view (P = 0.00007), 3.44° with the 45° Dunn view (P = 0.004) and 13.47° with the cross-table view (P = 0.002).
  
  
  CONCLUSIONS
  This experimental study confirmed the value of the frog-leg 45/45/30 view in assisting diagnosis of cam-type FAI.
authors.affiliation: Institut de l'Appareil Locomoteur, Rangueil University Hospital, Toulouse, France. cavaignac.etienne@gmail.com
authors.forename: Etienne
authors.initials: E
authors.lastname: Cavaignac
authors.forename: Philippe
authors.initials: P
authors.lastname: Chiron
authors.forename: Aloïs
authors.initials: A
authors.lastname: Espié
authors.forename: Nicolas
authors.initials: N
authors.lastname: Reina
authors.forename: Benoît
authors.initials: B
authors.lastname: Lepage
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Laffosse
mesh_terms: D001175:Arthrography / Q000379:methods*; D057925:Femoracetabular Impingement / Q000175:diagnosis* / Q000000981:diagnostic imaging; D005270:Femur Head / Q000000981:diagnostic imaging*; D005272:Femur Neck / Q000000981:diagnostic imaging*; D006621:Hip Joint / Q000000981:diagnostic imaging*; D006801:Humans; D008953:Models, Anatomic; D011187:Posture