title: Accuracy of acetabular component positioning with a fluoroscopically referenced CAOS system.
abstract: OBJECTIVE
  This study evaluated the accuracy, repeatability, and reproducibility of a fluoroscopic referenced system used for guiding acetabular component positioning.
  
  
  METHODS
  Calibration of the Medtronic StealthStation Treon Plus system was performed using a Weber gage block to assess linearity. Metrologic validation of repeatability and reproducibility was done using a cadaveric pelvis with an uncemented cup placed in the target position of 45 degrees inclination and 17.5 degrees anteversion. A baseline assessment was done with a National Institute of Standards and Technology (NIST) traceable coordinate measuring machine (CMM).
  
  
  RESULTS
  Weber gage block analysis revealed a mean bias of 0.69 mm. For the cadaveric pelvis, the anterior pelvic plane was determined using the bilateral anterior superior iliac spines with the symphysis pubis as the inferior landmark. The mean CMM measurement was inclination of 46.023 degrees (SD=1.075; range: 43.318-46.844 degrees) and anteversion of 15.787 degrees (SD=0.411; range: 15.068-16.384 degrees). One surgeon performed a repeatability assessment (n=8), finding mean inclination of 42.8 degrees (SD=1.5; range: 39.5-44.5 degrees) and anteversion of 17.5 degrees (SD=3.0; range: 14.5-22.5 degrees). Three surgeons performed a reproducibility assessment (n=24), finding mean overall inclination of 48.5 degrees (SD=0.9; range: 46-50 degrees) and anteversion of 17.8 degrees (SD=2.5; range: 13.5-23.5 degrees). All measurements were within a predefined acceptability range of+/-5 degrees.
  
  
  CONCLUSIONS
  The accuracy and reproducibility of the fluoroscopic referencing method was found to be suitable for determination of cup position in the surgical setting. Anteversion measurements were more variable for the fluoroscopic method and this may be related to the difficulty for the surgeon in predictably picking the anatomical points from the fluoroscopic image.
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: Mark
authors.initials: M
authors.lastname: Lazzeri
mesh_terms: D000077:Acetabulum; D019644:Arthroplasty, Replacement, Hip; D002102:Cadaver; D005471:Fluoroscopy; D006801:Humans; D015203:Reproducibility of Results; D025321:Surgery, Computer-Assisted