title: Do CAS measurements correlate with EOS 3D alignment measurements in primary TKA?
abstract: OBJECTIVE
  Objective of this study was to compare intraoperative computer-assisted surgery (CAS) alignment measurements during total knee arthroplasty (TKA) with pre- and postoperative coronal alignment measurements using EOS 3D reconstructions.
  
  
  METHODS
  In a prospective study, 56 TKAs using imageless CAS were performed and coronal alignment measurements were recorded twice: before bone cuts were made and after implantation of the prosthesis. Pre- and postoperative coronal alignment measurements were performed using EOS 3D reconstructions. Thanks to the EOS radiostereography system, measurement errors due to malpositioning and deformity during acquisition are eliminated. CAS measurements were compared with EOS 3D reconstructions. Varus/valgus angle (VV), mechanical lateral distal femoral angle (mLDFA) and mechanical medial proximal tibial angle (mMPTA) were measured.
  
  
  RESULTS
  Significantly different VV angles were measured pre- and postoperatively with CAS compared to EOS. For preoperative measurements, mLDFA did not differ significantly, but a significantly larger mMPTA in valgus was measured with CAS.
  
  
  CONCLUSIONS
  Results of this study indicate that differences in alignment measurements between CAS measurements and pre- and postoperative EOS 3D are due mainly to the difference between weight-bearing and non-weight-bearing position and potential errors in validity and reliability of the CAS system. EOS 3D measurements overestimate VV angle in lower limbs with substantial mechanical axis deviation. For lower limbs with minor mechanical axis deviation as well as for mMPTA measurements, CAS measures more valgus than EOS. Eventually the results of this study are of clinical relevance, since it raises concerns regarding the validity and reliability of CAS systems in TKA.
  
  
  METHODS
  IIb.
authors.affiliation: Department of Orthopaedics, University of Groningen, University Medical Center Groningen, PO Box 30.001, 9700 RB, Groningen, The Netherlands. m.f.meijer@umcg.nl.
authors.forename: Marrigje F
authors.initials: MF
authors.lastname: Meijer
authors.affiliation: Department of Orthopaedics, University of Groningen, University Medical Center Groningen, PO Box 30.001, 9700 RB, Groningen, The Netherlands.
authors.forename: Alexander L
authors.initials: AL
authors.lastname: Boerboom
authors.affiliation: Department of Orthopaedics, University of Groningen, University Medical Center Groningen, PO Box 30.001, 9700 RB, Groningen, The Netherlands.
authors.forename: Sjoerd K
authors.initials: SK
authors.lastname: Bulstra
authors.affiliation: Department of Trauma Surgery, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Inge H F
authors.initials: IHF
authors.lastname: Reininga
authors.affiliation: Department of Orthopaedics, University of Groningen, University Medical Center Groningen, PO Box 30.001, 9700 RB, Groningen, The Netherlands.
authors.forename: Martin
authors.initials: M
authors.lastname: Stevens
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D011300:Preoperative Care; D011446:Prospective Studies; D015203:Reproducibility of Results; D025321:Surgery, Computer-Assisted
keywords: CAS; Computer navigation; Computer-assisted surgery; Coronal alignment; Long-leg radiograph; TKA; TKR; Total knee arthroplasty; Total knee replacement