title: Optimal anterior femoral offset for functional range of motion in total hip arthroplasty--a computer simulation study.
abstract: OBJECTIVE
  Compared to medial femoral offset (MFO), the role of anterior femoral offset (AFO) on range of motion (ROM) in total hip arthroplasty (THA) has not been fully examined. We therefore defined AFO as the anterior distance from the centre of the femoral head to the proximal femoral axis in the sagittal plane and determined the optimal AFO required for ROM needed for activities of daily living using a computer-simulated THA model.
  
  
  METHODS
  Various AFOs were obtained by changing stem anteversion (stem-AV) and stem tilt in the sagittal plane (stem-tilt) using a CT-based simulation software. The required ROM was defined as: flexion ≥ 110°, internal rotation at 90° flexion (IR) ≥ 30°, external rotation (ER) ≥ 30°, and extension ≥ 30°, and we determined AFO and MFO to satisfy required ROM.
  
  
  RESULTS
  AFO was positively correlated with stem-AV and anterior stem-tilt. MFO was negatively correlated with stem-AV and not influenced by stem-tilt. Flexion and IR increased with both increased AFO and MFO, whereas extension and ER decreased with increased AFO. A smoothing spline curve showed the optimal AFO and MFO for required ROM to be from 15 mm to 25 mm on average and more than 32.1 mm, respectively.
  
  
  CONCLUSIONS
  This is the first study to show that AFO directly influenced ROM in THA. Optimal AFO as well as MFO should be reconstructed to achieve sufficient ROM.
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582, Japan.
authors.forename: Masanobu
authors.initials: M
authors.lastname: Hirata
authors.forename: Yasuharu
authors.initials: Y
authors.lastname: Nakashima
authors.forename: Daisuke
authors.initials: D
authors.lastname: Hara
authors.forename: Masayuki
authors.initials: M
authors.lastname: Kanazawa
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Kohno
authors.forename: Kensei
authors.initials: K
authors.lastname: Yoshimoto
authors.forename: Yukihide
authors.initials: Y
authors.lastname: Iwamoto
mesh_terms: D000203:Activities of Daily Living; D000328:Adult; D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D003198:Computer Simulation; D005260:Female; D005269:Femur / Q000033:anatomy & histology / Q000502:physiology / Q000601:surgery*; D006621:Hip Joint / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular / Q000502:physiology*