title: Pelvic tracker effects on hip center accuracy using imageless navigation.
abstract: OBJECTIVE
  Imageless computer assisted total knee surgical systems have commonly relied on determination of the functional rotational center of the femoral head as a landmark for determining the lower extremity mechanical axis. This has been accomplished through range of motion and center of rotation calculations for the femur with respect to the pelvis as the lower extremity is taken through a range of motion. Our study evaluated the use of this algorithm with and without a pelvic tracker attached to the iliac crest.
  
  
  METHODS
  The functional center of the hip joint was also compared to the true radiographic center as determined by spiral CT data. Evaluating the different methods on six lower extremities from three whole-body cadavers revealed significant differences in the location of the calculated hip joint center, but little difference in the resulting lower extremity mechanical axis determination. The functional hip joint centers measured with and without a pelvic tracker differed from one another and from the CT-determined hip center.
  
  
  RESULTS
  No differences were found in the coronal plane measurements, but statistically significant differences were found in the sagittal plane measurements.
  
  
  CONCLUSIONS
  Algorithms that reduce the noise generated by pelvic movement should be devised to eliminate the need for a pelvic tracker.
authors.affiliation: Department of Orthopedic Surgery, State University of New York, Buffalo, NY, USA. wmm4n@virginia.edu
authors.forename: William M
authors.initials: WM
authors.lastname: Mihalko
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Phillips
authors.forename: Zair
authors.initials: Z
authors.lastname: Fishkin
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Krackow
mesh_terms: D000465:Algorithms; D002102:Cadaver; D006621:Hip Joint / Q000000981:diagnostic imaging; D006801:Humans; D007717:Knee / Q000601:surgery*; D016059:Range of Motion, Articular; D012399:Rotation; D025321:Surgery, Computer-Assisted / Q000379:methods*; D014057:Tomography, X-Ray Computed