title: Accuracy of knee implants sizing predicted by digital images.
abstract: BACKGROUND
  Accurate preoperative templating to predict implant size and position can facilitate precise, efficient, and reproducible knee replacement operations. Preoperative templating for total knee arthroplasty can be performed with digital images of the knee implants on digital radiographs of the knee.
  
  
  OBJECTIVE
  To determine the accuracy of knee implants sizing predicted by digital images.
  
  
  METHODS
  A retrospective study was done to assess the accuracy of the knee implant sizing predicted by digital images in 100 Thai adults, who had osteoarthritis of the knee. Digital anteroposterior and lateral radiographs of the knee were used in measuring the level of distal femoral resection and the level of proximal tibial resection. Anteroposterior and mediolateral diameter of femur and tibia were determined and the implant size was choosen. The results from digital images were compared with the size of actual femoral and tibial implants used at the time of surgery. All variables were analyzed. The correlation coefficients were calculated to determine interobserver and intraobserver reliability.
  
  
  RESULTS
  The accuracy of digital preoperative plans for femoral component was 53.1%. The accuracy of digital preoperative plans for tibial component was 59.3%. The digital preoperative planning predicted 79 of 81 (97.6%) femoral implants to within one size and predicted 77 of 81 (95.1%) measurements of the tibial implants to within one size.
  
  
  CONCLUSIONS
  Digital images can help to focus the thoughts and plans of the operation. When planning is performed, it can identify extremes of sizes that may require special order, and planning can predict size mismatches between femoral and tibial implants. When recognized ahead of time, these limitations can be accommodated during the surgical procedure or a different implant system chosen. Predicting implant sizes to within one size allows efficient anticipation by the orthopaedic surgeon.
authors.affiliation: Department of Orthopaedics, Faculty of Medicine Ramathibodi Hospital, Mahidol Universit, Bangkok, Thailand. siwadolrama@hotmail.com
authors.forename: Siwadol
authors.initials: S
authors.lastname: Wongsak
authors.forename: Viroj
authors.initials: V
authors.lastname: Kawinwonggowit
authors.forename: Pornchai
authors.initials: P
authors.lastname: Mulpruck
authors.forename: Thanaphot
authors.initials: T
authors.lastname: Channoom
authors.forename: Patarawan
authors.initials: P
authors.lastname: Woratanarat
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000601:surgery; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011237:Predictive Value of Tests; D011300:Preoperative Care / Q000379:methods*; D017755:Prosthesis Fitting / Q000379:methods; D019919:Prosthesis Implantation / Q000379:methods; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D025321:Surgery, Computer-Assisted / Q000379:methods; D016896:Treatment Outcome