title: Does femoral rotation influence anteroposterior alpha angle, lateral center-edge angle, and medial proximal femoral angle? A pilot study.
abstract: BACKGROUND
  Femoral rotation on AP radiographs affects several parameters used to assess morphologic features of the proximal femur but its effect on femoroacetabular impingement parameters remains unknown.
  
  
  OBJECTIVE
  We therefore evaluated and characterized the potential effect of femoral rotation on (1) AP alpha angle, (2) lateral-center edge angle (LCEA), and (3) medial proximal femoral angle (MPFA) on AP hip radiographs.
  
  
  METHODS
  We took seven AP hip radiographs at intervals of successive femoral rotation on a single dry, cadaveric specimen: 60°, 40°, and 20° internal rotation; 0° neutral/anatomic rotation; and 20°, 40°, and 50° external rotation. The AP alpha angle, LCEA, and MPFA were measured on all radiographs by two independent evaluators.
  
  
  RESULTS
  Within the range of femoral rotation studied, the AP alpha angle ranged from 39° to 62°, the LCEA from 25° to 35°, and the MPFA from 70° to 115°. MPFA and AP alpha angle showed a linear relationship with femoral rotation. Each additional degree of internal rotation produced a reciprocal reduction of the MPFA by 0.36° and the AP alpha angle by 0.18° and vice versa in external rotation. The LCEA, especially within the internal rotation range, showed minimal variation.
  
  
  CONCLUSIONS
  These changes in radiographic parameters emphasize the importance of femoral rotation and patient positioning. We recommend radiographs be evaluated for excessive femoral rotation or nonstandardized positioning before interpretation for diagnostic and treatment implications. It may be prudent to repeat radiographs in these circumstances or, when standardized positioning is not feasible, proceed toward advance imaging.
authors.affiliation: Department of Orthopedic Surgery, Rady Children's Hospital and Health Center, 3030 Children's Way, Suite 410, San Diego, CA 92123, USA.
authors.forename: Shafagh
authors.initials: S
authors.lastname: Monazzam
authors.forename: James D
authors.initials: JD
authors.lastname: Bomar
authors.forename: Mandar
authors.initials: M
authors.lastname: Agashe
authors.forename: Harish S
authors.initials: HS
authors.lastname: Hosalkar
mesh_terms: D001696:Biomechanical Phenomena; D002102:Cadaver; D005269:Femur / Q000000981:diagnostic imaging / Q000502:physiology*; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000502:physiology*; D006801:Humans; D015588:Observer Variation; D056888:Patient Positioning; D010865:Pilot Projects; D011237:Predictive Value of Tests; D011859:Radiography; D016059:Range of Motion, Articular; D015203:Reproducibility of Results