title: Anterior and Posterior Femoral Head-Neck Offset Ratio in the Cam Impingement.
abstract: OBJECTIVE
  The purpose of this study was to determine if the anterior-posterior offset ratio is altered in patients with symptomatic cam impingement.
  
  
  METHODS
  Preoperative radiographs of 15 symptomatic patients with isolated cam-type impingement diagnosed by physical examination and magnetic resonance imaging arthrogram (MRIA) and confirmed by hip arthroscopy findings were assessed. Fifteen asymptomatic volunteers made up the control group. The anterior offset (AO), posterior offset (PO), and AO/PO ratio were calculated.
  
  
  RESULTS
  The mean ± SD AO/PO ratio was 0.56 ± 0.1 for the symptomatic group and 0.9 ± 0.2 for the asymptomatic group. This difference was statistically significant. Intra- and interobserver correlation factor for calculating the AO/PO ratio was 0.8 and 0.5, respectively, and differences were not statistically different.
  
  
  CONCLUSIONS
  The AO/PO ratio in this study was a useful radiological parameter for the assessment of patients with a cam-type impingement.
authors.affiliation: Department of Orthopaedic Surgery, Hospital Militar de Santiago, Santiago, Chile.
authors.forename: Fernando
authors.initials: F
authors.lastname: Nemtala
authors.affiliation: Department of Orthopaedic Surgery, Hospital Militar de Santiago, Santiago, Chile ; Department of Orthopaedic Surgery, Clínica Las Condes, Santiago, Chile.
authors.forename: Rodrigo M
authors.initials: RM
authors.lastname: Mardones
authors.affiliation: Department of Orthopaedic Surgery, Hospital Militar de Santiago, Santiago, Chile.
authors.forename: Alexander
authors.initials: A
authors.lastname: Tomic
keywords: cross table lateral radiograph; femoroacetabular impingement; offset