title: 2D versus 3D templating in total knee arthroplasty.
abstract: BACKGROUND
  Preoperative digital templating in total knee arthroplasty (TKA) helps to determine the need of non-standard implants, prophesies the bony resections and helps to anticipate the intraoperative plan. Templating within the process of patient specific instrumentation (PSI) is fairly new and 2D planning has not been compared to PSI templating.
  
  
  METHODS
  94 patients underwent unilateral primary TKA with magnetic resonance imaging (MRI) based preoperative templating and PSI cutting blocks. Parallel to this, three observers templated all cases using digital planning on standard preoperative x-rays. The examiners templated all cases independently and were blinded to the component sizes used intraoperatively.
  
  
  RESULTS
  Three-dimensional (3D) templating was accurate in predicting the correct implant size in 100% of the cases. The femoral and tibial two-dimensional (2D) digital templating varied from 43.6% to 59.5% and 52.1% to 68% of the cases. When allowing ±1 difference, femoral 2D digital templating varied from 93.6% to 97.8% of the cases and ranged from 94.6% to 98.9% on the tibial side. All observers show "very good" correlation. The coefficient indicates a very good agreement in between the three observers.
  
  
  CONCLUSIONS
  3D templating has very high accuracy for the actual implant size prediction. Compared to this, 2D digital templating is an accurate method to approximately (±1 size) determine the size of TKA components. However, we judge this technique accurate enough, that 2D templating allows launching Template-directed instrumentation (TDI), while the examiner does not need a high level of clinical experience.
  
  
  CONCLUSIONS
  Within the process of digital planning, the surgeonmight focus evenmore on the upcoming operation.
authors.affiliation: Department of Orthopedic Surgery, Hannover Medical School, Hanover, Germany. Electronic address: max@ettinger.info.
authors.forename: Max
authors.initials: M
authors.lastname: Ettinger
authors.affiliation: Department of Orthopedic Surgery, Hannover Medical School, Hanover, Germany.
authors.forename: Leif
authors.initials: L
authors.lastname: Claassen
authors.affiliation: Department of Orthopedic Surgery, Hannover Medical School, Hanover, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Paes
authors.affiliation: Department of Orthopedic Surgery, Hannover Medical School, Hanover, Germany.
authors.forename: Tilman
authors.initials: T
authors.lastname: Calliess
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000601:surgery; D007720:Knee Prosthesis; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D020370:Osteoarthritis, Knee / Q000175:diagnosis / Q000601:surgery*; D012372:ROC Curve; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D025321:Surgery, Computer-Assisted / Q000379:methods*
keywords: Templating; Total knee arthroplasty; Training level