title: Acetabular orientation: anatomical and functional measurement.
abstract: OBJECTIVE
  Acetabular orientation is important to consider in hip joint pathology and treatment. This study aims to describe the functional orientation of the acetabulum as a representative measure of force transmitted through the hip joint generated from bone density mapping and compare it to landmark-based anatomical orientation measures.
  
  
  METHODS
  CT scans of 38 non-pathologic individuals were analyzed. Functional orientation was computed as the density-weighted average of the acetabular surface normals based on surface density maps. Two anatomical measures were also used to describe the orientation of each acetabulum: the normal to the acetabular rim plane and the abduction angle based on AP pelvic "Radiographs" generated from the CT data.
  
  
  RESULTS
  The average functional and anatomic abduction and anteversion angles ranged from 32°-58° and 22°-31°, respectively, with significant side-to-side correlation in individual patients for the majority of measures. Functional acetabular orientation was weakly correlated only with the rim plane measure. Native acetabular abduction in the 3D anatomic and functional methods was significantly shallower than the 2D "Radiographic" measure. The vector generated to describe functional acetabular orientation was found to be more vertically and posteriorly oriented than the anatomic measures.
  
  
  CONCLUSIONS
  Functional acetabular orientation, reflecting the calculated directionality of the subchondral bone density, yields a more posterior and vertical measure of acetabular orientation as compared to the direction of load transmission suggested by the anatomic methods.
authors.affiliation: Orthopaedic Biomechanics Laboratory, Sunnybrook Health Sciences Centre, UB19, 2075 Bayview Avenue, Toronto, ON, M4N 3M5, Canada. omrilu@gmail.com
authors.forename: Omri
authors.initials: O
authors.lastname: Lubovsky
authors.forename: David
authors.initials: D
authors.lastname: Wright
authors.forename: Michael
authors.initials: M
authors.lastname: Hardisty
authors.forename: Alex
authors.initials: A
authors.lastname: Kiss
authors.forename: Hans
authors.initials: H
authors.lastname: Kreder
authors.forename: Cari
authors.initials: C
authors.lastname: Whyne
mesh_terms: D000077:Acetabulum / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D059925:Anatomic Landmarks; D015331:Cohort Studies; D005260:Female; D005270:Femur Head / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D006621:Hip Joint / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D006801:Humans; D008297:Male; D008875:Middle Aged; D011856:Radiographic Image Enhancement / Q000379:methods*; D016059:Range of Motion, Articular / Q000502:physiology*; D012016:Reference Values; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*