title: Femoral head-neck offset measurements in 339 subjects: distribution and implications for femoroacetabular impingement.
abstract: OBJECTIVE
  The α-angle is a frequently used measurement to quantify head-neck offset pathology in cam-type femoroacetabular impingement. However, diverging norm values and reference intervals have been described, especially in men.
  
  
  METHODS
  The α-angle, the head-neck offset ratio and the triangular index were measured on anteroposterior and lateral radiographs of 339 (170 men and 169 women) subjects without evident underlying hip pathology.
  
  
  RESULTS
  For male subjects, the mean α-angle was 49.4° (SD 10.5°) on anteroposterior and 49.1° (SD 10.6°) on lateral radiographs, whereas for female subjects, it was 45.0° (SD 8.0°) and 46.1° (SD 9.9°), respectively. Thus, calculated upper limits of reference intervals in the population screened were 70° for both radiographic projections in men and 61° (anteroposterior) and 66° (lateral) in women.
  
  
  CONCLUSIONS
  These data substantiate recent findings that the pathological threshold of the α-angle in male subjects may be lower than that previously assumed.
  
  
  METHODS
  Diagnostic, Level III.
authors.affiliation: Department of Orthopaedic Surgery, University of Ulm, Oberer Eselsberg 45, 89081, Ulm, Germany. christian.fraitzl@uni-ulm.de
authors.forename: Christian R
authors.initials: CR
authors.lastname: Fraitzl
authors.forename: Thomas
authors.initials: T
authors.lastname: Kappe
authors.forename: Friederike
authors.initials: F
authors.lastname: Pennekamp
authors.forename: Heiko
authors.initials: H
authors.lastname: Reichel
authors.forename: Christian
authors.initials: C
authors.lastname: Billich
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001837:Body Weights and Measures; D005260:Female; D005270:Femur Head / Q000000981:diagnostic imaging*; D005272:Femur Neck / Q000000981:diagnostic imaging*; D006621:Hip Joint / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011859:Radiography; D055815:Young Adult