title: Navigated intraoperative analysis of lower limb alignment.
abstract: BACKGROUND
  Accurate intraoperative assessment of lower limb alignment is crucial for the treatment of long bone fractures, implantation of knee arthroplasties and correction of deformities. During orthopaedic surgery, exact real time control of the mechanical axis is strongly desirable. The aim of this study was to compare conventional intraoperative analysis of the mechanical axis by the cable method with continuous, 3-dimensional imaging with a navigation system.
  
  
  METHODS
  Twenty legs of fresh human cadaver were randomly assigned to conventional analysis with the cable method (n = 10) or navigated analysis with a fluoroscopy based navigation system (n = 10). The intersection of the mechanical axis with the tibia plateau was presented as percentage of the tibia plateau (beginning with 0% at the medial border and ending with 100% laterally). CT-scans were performed for all legs and the CT-values of the mechanical axis were compared to the measurements after cable method and navigation. Furthermore, the radiation time and dose area product of both groups for single analysis of the mechanical axis was compared.
  
  
  RESULTS
  Conventional evaluation of the mechanical axis by the cable method showed 6.0+/-3.1% difference compared to the analysis by CT. In the navigated group the difference was 2.6+/-1.8% (P = 0.008). Radiation time and dose area product were highly significantly lower after conventional measurement.
  
  
  CONCLUSIONS
  Navigated intraoperative evaluation of the mechanical axis offers increased accuracy compared to conventional intraoperative analysis. Furthermore, navigation provides continuous control not only of the mechanical axis, but also of the sagittal and transverse plane. Using the cable method, radiation exposure depends on the number of measurements and is lower compared to the navigation system for single intraoperative analysis of the mechanical axis, but may be higher in case of repeated intraoperative measurements.
authors.affiliation: Trauma Department, Hannover Medical School (MHH), Carl-Neuberg-Str. 1, 30625 Hannover, Germany. hankemeier.stefan@mh-hannover.de
authors.forename: Stefan
authors.initials: S
authors.lastname: Hankemeier
authors.forename: Tobias
authors.initials: T
authors.lastname: Hufner
authors.forename: Gongli
authors.initials: G
authors.lastname: Wang
authors.forename: Daniel
authors.initials: D
authors.lastname: Kendoff
authors.forename: Guoyan
authors.initials: G
authors.lastname: Zheng
authors.forename: Martinus
authors.initials: M
authors.lastname: Richter
authors.forename: Thomas
authors.initials: T
authors.lastname: Gosling
authors.forename: Lutz
authors.initials: L
authors.lastname: Nolte
authors.forename: Christian
authors.initials: C
authors.lastname: Krettek
mesh_terms: D019645:Arthroplasty, Replacement, Knee; D002102:Cadaver; D006801:Humans; D021621:Imaging, Three-Dimensional; D035002:Lower Extremity / Q000000981:diagnostic imaging* / Q000601:surgery; D016343:Monitoring, Intraoperative / Q000295:instrumentation; D013977:Tibia / Q000000981:diagnostic imaging* / Q000601:surgery; D014057:Tomography, X-Ray Computed