title: The association between Femoral Tilt and impingement-free range-of-motion in total hip arthroplasty.
abstract: BACKGROUND
  There is a complex interaction among acetabular component position and antetorsion of the femoral stem in determining the maximum, impingement-free prosthetic range-of-motion (ROM) in total hip arthroplasty (THA). By insertion into the femoral canal, stems of any geometry follow the natural anterior bow of the proximal femur, creating a sagittal Femoral Tilt (FT). We sought to study the incidence of FT as measured on postoperative computed tomography scans and its influence on impingement-free ROM in THA.
  
  
  METHODS
  The incidence of the postoperative FT was evaluated on 40 computed tomography scans after cementless THA. With the help of a three-dimensional computer model of the hip, we then systematically analyzed the effects of FT on femoral antetorsion and its influence on calculations for a ROM maximized and impingement-free compliant stem/cup orientation.
  
  
  RESULTS
  The mean postoperative FT on CT scans was 5.7° ± 1.8°. In all tests, FT significantly influenced the antetorsion values. Re-calculating the compliant component positions according to the concept of combined anteversion with and without the influence of FT revealed that the zone of compliance could differ by more than 200%. For a 7° change in FT, the impingement-free cup position differed by 4° for inclination when the same antetorsion was used.
  
  
  CONCLUSIONS
  A range-of-motion optimized cup position in THA cannot be calculated based on antetorsion values alone. The FT has a significant impact on recommended cup positions within the concept of "femur first" or "combined anteversion". Ignoring FT may pose an increased risk of impingement as well as dislocation.
authors.affiliation: Department of Orthopaedic Surgery, Regensburg University Medical Center, Regensburg, Germany. t.renkawitz@asklepios.com
authors.forename: Tobias
authors.initials: T
authors.lastname: Renkawitz
authors.forename: Martin
authors.initials: M
authors.lastname: Haimerl
authors.forename: Lars
authors.initials: L
authors.lastname: Dohmen
authors.forename: Sabine
authors.initials: S
authors.lastname: Gneiting
authors.forename: Philipp
authors.initials: P
authors.lastname: Lechler
authors.forename: Michael
authors.initials: M
authors.lastname: Woerner
authors.forename: Hans-Robert
authors.initials: HR
authors.lastname: Springorum
authors.forename: Markus
authors.initials: M
authors.lastname: Weber
authors.forename: Patrick
authors.initials: P
authors.lastname: Sussmann
authors.forename: Ernst
authors.initials: E
authors.lastname: Sendtner
authors.forename: Joachim
authors.initials: J
authors.lastname: Grifka
mesh_terms: D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000379:methods*; D060750:Bone Anteversion / Q000000981:diagnostic imaging / Q000209:etiology / Q000503:physiopathology*; D002484:Cementation; D005260:Female; D057925:Femoracetabular Impingement / Q000000981:diagnostic imaging / Q000209:etiology / Q000503:physiopathology*; D005269:Femur / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery; D006621:Hip Joint / Q000503:physiopathology* / Q000601:surgery; D006622:Hip Prosthesis; D006801:Humans; D004204:Joint Dislocations / Q000000981:diagnostic imaging / Q000209:etiology / Q000503:physiopathology*; D008297:Male; D011183:Postoperative Complications / Q000503:physiopathology; D016059:Range of Motion, Articular; D014057:Tomography, X-Ray Computed