title: Radiographic measurement of the posterior femoral offset is not precise.
abstract: OBJECTIVE
  The posterior femoral offset may significantly impact the final flexion range after total knee arthroplasty (TKA). The purpose of the present study was to compare a conventional, radiologic-based technique with an intra-operative, surgical navigation-based technique for the measurement of posterior femoral offset. The tested hypothesis was that the two measurement techniques produce different results both before and after TKA.
  
  
  METHODS
  One-hundred consecutive cases referred for end-stage knee osteoarthritis have been studied. Posterior femoral offsets, measured pre- and post-TKA from radiographs, as well as those measured from a navigation system intra-operatively, were analysed. The pre-TKA measured offsets, post-TKA measured offsets and the changes (pre- vs. post-TKA) in the offsets were statistically compared between the radiologic and the navigated measurement techniques at a 0.05 level of significance.
  
  
  RESULTS
  The mean paired difference between pre-TKA radiologic and navigated measurement was 4 ± 4 mm (p < 0.001). There was a significant and moderate positive correlation with a good coherence between the two measurements. The mean paired difference between post-TKA radiologic and navigated measurement was 6 ± 5 mm (p < 0.001). There was a significant and moderate positive correlation but a poor coherence between the two measurements.
  
  
  CONCLUSIONS
  The conventional radiologic technique for the measurement of the posterior femoral offset cannot be reliably used either for pre-TKA planning of the posterior femoral resection and antero-posterior sizing of the femoral component, or for post-TKA quality control of the reconstruction of the posterior femoral offset.
  
  
  METHODS
  Level IV.
authors.affiliation: CCOM, University Hospital Strasbourg, 10 Avenue Baumann, 67400, Illkirch-Graffenstaden, France. jean-yves.jenny@chru-strasbourg.fr.
authors.forename: Jean-Yves
authors.initials: JY
authors.lastname: Jenny
authors.affiliation: CCOM, University Hospital Strasbourg, 10 Avenue Baumann, 67400, Illkirch-Graffenstaden, France.
authors.forename: Sophie
authors.initials: S
authors.lastname: Honecker
authors.affiliation: CCOM, University Hospital Strasbourg, 10 Avenue Baumann, 67400, Illkirch-Graffenstaden, France.
authors.forename: Yves
authors.initials: Y
authors.lastname: Chammai
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging* / Q000601:surgery*; D006801:Humans; D007719:Knee Joint / Q000601:surgery; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000601:surgery; D011859:Radiography; D016059:Range of Motion, Articular
keywords: Knee joint; Navigation; Posterior femoral offset; Radiologic measurement; Total knee arthroplasty; Total knee replacement