title: Measuring leg length and offset with an imageless navigation system during total hip arthroplasty: is it really accurate?
abstract: BACKGROUND
  A novel imageless measurement algorithm to assess leg length (LL) and offset (OS) changes during total hip arthroplasty (THA) has been established, the purpose of this study was to describe the process and establish whether or not it is accurate.
  
  
  METHODS
  THA was performed on 17 cadaver hip specimens. LL and OS changes were determined intra-operatively, using an imageless navigation system. Pre- and postoperatively, all specimens had a computed tomography scan (CT) and the LL and OS changes were analysed by two blinded investigators.
  
  
  RESULTS
  With mean differences of less than 1 mm (LL, 0.74; SD, 2.4 mm; OS, 0.89; SD, 1.8 mm) supported by substantial significant correlations [r = 0.83 (LL) and r = 0.92 (OS)] imageless navigation values demonstrated a high accuracy when compared to CT measurements.
  
  
  CONCLUSIONS
  Intra-operative LL and OS measures are reliable and accurate when using an imageless calculation algorithm which stores the position of the femoral reference frame in relation to the pelvic coordinate system before and after reconstruction.
authors.affiliation: Department of Orthopaedic Surgery, Regensburg University Medical Centre, sklepios Klinikum Bad Abbach, Bad Abbach, Germany. tobias.renkawitz@web.de
authors.forename: Tobias
authors.initials: T
authors.lastname: Renkawitz
authors.forename: Tibor
authors.initials: T
authors.lastname: Schuster
authors.forename: Thomas
authors.initials: T
authors.lastname: Herold
authors.forename: Holger
authors.initials: H
authors.lastname: Goessmann
authors.forename: Ernst
authors.initials: E
authors.lastname: Sendtner
authors.forename: Joachim
authors.initials: J
authors.lastname: Grifka
authors.forename: Thomas
authors.initials: T
authors.lastname: Kalteis
mesh_terms: D000465:Algorithms; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000379:methods* / Q000706:statistics & numerical data; D002102:Cadaver; D003198:Computer Simulation; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007870:Leg Length Inequality / Q000000981:diagnostic imaging / Q000517:prevention & control*; D008297:Male; D019060:Minimally Invasive Surgical Procedures / Q000379:methods / Q000706:statistics & numerical data; D011183:Postoperative Complications / Q000000981:diagnostic imaging / Q000517:prevention & control*; D012371:Robotics / Q000379:methods* / Q000706:statistics & numerical data; D025321:Surgery, Computer-Assisted / Q000379:methods* / Q000706:statistics & numerical data; D014057:Tomography, X-Ray Computed