title: Experience of total knee arthroplasty using a novel navigation system within the surgical field.
abstract: BACKGROUND
  With the aim of improving component alignment and outcome in total knee arthroplasty (TKA), several computer-assisted devices (CAD) have been developed.
  
  
  METHODS
  In February 2014, the present unit started to use a new imageless navigation system with accelerometric pods within the surgical field for all primary TKAs; there was no need for optical trackers or cameras. This paper presents the results of the first 72 TKAs using this iAssist system in 71 prospectively collected and retrospectively analyzed patients. It analyzed component positioning in standard and full-length leg x-rays.
  
  
  RESULTS
  The mean age of the patients was 70years (range 52-88). The center of hip, knee and ankle (mechanical axes) deviated on average 0.5° (standard deviation (SD) of 1.8) valgus from the targeted straight alignment. Three TKAs had >3° deviation (i.e. four degree varus, five degree and seven degree valgus). The frontal tibial tray alignment was an average of 89.9° (range 86.4-100.1°, SD ±2.0) with the target being 90°, and the sagittal slope was as targeted at 85.0° (range 78.4-88.8°, SD ±1.7).
  
  
  CONCLUSIONS
  This CAD facilitated good mechanical alignment and reproducible accuracy in component positioning. Pods clipped onto cutting jigs within the surgical field provided simple and accurate navigation, with little extra time needed for calibration and no need for optical trackers or pre-operative imaging.
authors.affiliation: Department of Orthopaedic Surgery, Kantonsspital Uri (KSU), CH-6460 Altdorf, Switzerland; Balgrist University Hospital, CH 8008 Zurich, Switzerland.
authors.forename: Richard
authors.initials: R
authors.lastname: Niehaus
authors.affiliation: Department of Orthopaedic Surgery, Kantonsspital Uri (KSU), CH-6460 Altdorf, Switzerland.
authors.forename: David
authors.initials: D
authors.lastname: Schilter
authors.affiliation: Department of Orthopaedic Surgery, I'HFR Fribourg, Hôpital Cantonal, CH-1700 Fribourg, Switzerland.
authors.forename: Paolo
authors.initials: P
authors.lastname: Fornaciari
authors.affiliation: Department of Plastic and Aesthetic Surgery, Dietrich-Bonhoeffer-Klinikum, Universität Greifswald, 17033 Neubrandenburg, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Weinand
authors.affiliation: Department of Orthopaedic Surgery, Kantonsspital Uri (KSU), CH-6460 Altdorf, Switzerland.
authors.forename: Marcus
authors.initials: M
authors.lastname: Boyd
authors.affiliation: Department of Orthopaedic Surgery, Kantonsspital Uri (KSU), CH-6460 Altdorf, Switzerland.
authors.forename: Marcel
authors.initials: M
authors.lastname: Ziswiler
authors.affiliation: Department of Orthopaedic Surgery, Kantonsspital Uri (KSU), CH-6460 Altdorf, Switzerland. Electronic address: stefanehre@hotmail.com.
authors.forename: Stefan
authors.initials: S
authors.lastname: Ehrendorfer
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000601:surgery; D035002:Lower Extremity / Q000000981:diagnostic imaging; D008297:Male; D008875:Middle Aged; D061646:Operative Time; D011446:Prospective Studies; D016059:Range of Motion, Articular; D012086:Reoperation; D012189:Retrospective Studies; D012984:Software; D025321:Surgery, Computer-Assisted / Q000295:instrumentation / Q000379:methods*
keywords: Computer-assisted TKA; Knee replacement; Navigated knee; Total knee arthroplasty, TKA; iAssist