title: Comparison of fluoroscopic and imageless registration in surgical navigation of the acetabular component.
abstract: OBJECTIVE
  This study compared the repeatability and reproducibility of acetabular component positioning using imageless and fluoroscopic-referenced navigation methods.
  
  
  METHODS
  A single cadaveric pelvis had a modular acetabular component securely fixed. Cup position was evaluated using imageless and fluoroscopic registration techniques. These were compared to measurements of a coordinate measuring machine (CMM) and a validated CT scan protocol.
  
  
  RESULTS
  The CMM-determined anatomical acetabular inclination measurement was 46.02 degrees (SD = 1.07), while the CMM-determined anatomical anteversion (pubic symphysis) was 15.79 degrees (SD = 0.41). Computed tomography revealed inclination of 42.2 degrees (SD = 0.65); anteversion with pubic tubercle referencing of 12.1 degrees (SD = 0.14); and anteversion with pubic symphysis referencing of 14.3 degrees (SD = 0.89). Evaluation of repeatability (one surgeon; n = 8) with the imageless system (pubic tubercle) revealed inclination of 41.8 degrees (SD = 0.46) and anteversion of 11.2 degrees (SD = 0.8). For the fluoroscopic system (pubic symphysis), inclination was 42.8 degrees (SD = 1.6) and anteversion was 17.6 degrees (SD = 3.1). Evaluation of reproducibility (three surgeons; n = 24) with the imageless system revealed inclination of 41.8 degrees (SD = 0.82) and anteversion of 15.2 degrees (SD = 1.06). For the fluoroscopic system, inclination was 48.5 degrees (SD = 0.9) and anteversion was 17.8 degrees (SD = 2.5). Imageless referencing of cup inclination and anteversion were found to be process capable using the Six Sigma Cp and Cpk capability indices. Fluoroscopic referencing was process capable for cup inclination but not for cup anteversion (Cp - 1.1; Cpk - 1.0). An F-test revealed significantly greater variance with fluoroscopic referenced anteversion (p < 0.002).
  
  
  CONCLUSIONS
  Imageless referencing was process capable for computer navigation of cup placement in the ex-vivo setting. Fluoroscopic referencing for pelvic landmarks is problematic as locating points from radiographic images is difficult, especially for cup anteversion.
authors.affiliation: Department of Orthopaedic Surgery, Medical College of Wisconsin, Columbia-St Mary's Hospital, Milwaukee, Wisconsin, USA. jbstiehl@aol.com
authors.forename: James B
authors.initials: JB
authors.lastname: Stiehl
authors.forename: David A
authors.initials: DA
authors.lastname: Heck
authors.forename: Branislav
authors.initials: B
authors.lastname: Jaramaz
authors.forename: Louis-Phillipe
authors.initials: LP
authors.lastname: Amiot
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D002102:Cadaver; D005471:Fluoroscopy / Q000379:methods* / Q000706:statistics & numerical data; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods* / Q000706:statistics & numerical data; D011630:Pubic Bone / Q000000981:diagnostic imaging / Q000473:pathology; D015203:Reproducibility of Results; D025321:Surgery, Computer-Assisted / Q000379:methods* / Q000706:statistics & numerical data; D014057:Tomography, X-Ray Computed / Q000379:methods / Q000706:statistics & numerical data