title: Patient-specific instrumentation for total knee arthroplasty does not match the pre-operative plan as assessed by intra-operative computer-assisted navigation.
abstract: OBJECTIVE
  The introduction of patient-specific instruments (PSI) for guiding bone cuts could increase the incidence of malalignment in primary total knee arthroplasty. The purpose of this study was to assess the agreement between one type of patient-specific instrumentation (Zimmer PSI) and the pre-operative plan with respect to bone cuts and component alignment during TKR using imageless computer navigation.
  
  
  METHODS
  A consecutive series of 30 femoral and tibial guides were assessed in-theatre by the same surgeon using computer navigation. Following surgical exposure, the PSI cutting guides were placed on the joint surface and alignment assessed using the navigation tracker. The difference between in-theatre data and the pre-operative plan was recorded and analysed.
  
  
  RESULTS
  The error between in-theatre measurements and pre-operative plan for the femoral and tibial components exceeded 3° for 3 and 17% of the sample, respectively, while the error for total coronal alignment exceeded 3° for 27% of the sample.
  
  
  CONCLUSIONS
  The present results indicate that alignment with Zimmer PSI cutting blocks, assessed by imageless navigation, does not match the pre-operative plan in a proportion of cases. To prevent unnecessary increases in the incidence of malalignment in primary TKR, it is recommended that these devices should not be used without objective verification of alignment, either in real-time or with post-operative imaging. Further work is required to identify the source of discrepancies and validate these devices prior to routine use.
  
  
  METHODS
  II.
authors.affiliation: Sydney Orthopaedic Research Institute, Suite 13, Level 1, 445 Victoria Avenue, Chatswood, NSW, 2067, Australia, cscholes@sori.com.au.
authors.forename: Corey
authors.initials: C
authors.lastname: Scholes
authors.forename: Varun
authors.initials: V
authors.lastname: Sahni
authors.forename: Sebastien
authors.initials: S
authors.lastname: Lustig
authors.forename: David A
authors.initials: DA
authors.lastname: Parker
authors.forename: Myles R J
authors.initials: MR
authors.lastname: Coolican
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects* / Q000295:instrumentation / Q000379:methods; D017760:Bone Malalignment / Q000175:diagnosis / Q000209:etiology*; D005260:Female; D005269:Femur / Q000601:surgery; D006801:Humans; D007432:Intraoperative Period; D007720:Knee Prosthesis; D008297:Male; D019300:Medical Errors / Q000009:adverse effects*; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000601:surgery*; D057234:Preoperative Period; D025321:Surgery, Computer-Assisted / Q000009:adverse effects* / Q000379:methods; D013977:Tibia / Q000601:surgery; D016896:Treatment Outcome
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