Accuracy of Knee Implants Sizing Predicted by Digital Images
Siwadol Wongsak MD*, Viroj Kawinwonggowit MD*, Pornchai Mulpruck MD*, Thanaphot Channoom MD*, Patarawan Woratanarat MD, PhD*
Affiliation : * Department of Orthopaedics, Faculty of Medicine Ramathibodi Hospital, Mahidol Universit, Bangkok, Thailand
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.
Material and method: 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.
Conclusion : 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.
Keywords : Total knee arthroplasty, Preoperative planning, Digital images
