Imprecise prediction of implant sizes with preoperative 2D digital templating in total knee arthroplasty

Purpose To analyze the match between preoperatively determined implant size (2D templating) and intraoperatively used implant size in total knee arthroplasty (TKA). Also examined were the factors that might influence templating accuracy (gender, surgeon experience, obesity, etc.). Materials and methods The study was retrospective and conducted in a specialized ENDOCERT arthroplasty center. Digital templating was done with the MediCAD software. If the planned and implanted TKA components (both femur and tibia) were the same size, the match was classified “exact.” A deviation of ± one size (at the femur or tibia or both) was classified “accurate.” A deviation of ± two or more sizes (at the femur or tibia or both) was classified “inaccurate.” Obesity, gender, implant type and surgeon experience were investigated for potential influence on templating accuracy. Chi-square tests and Cohen’s weighted kappa test were used for statistical analysis. Results A total of 482 cases [33.6% male, 66.4% female, age 69 ± 11, body mass index (BMI) 30.3 ± 5.8] were included. When the femur and tibia were taken together, exact size match was observed in 34% (95% CI 29.9–38.3%) of cases, accurate size match in 57.5% (95% CI 53–61.8%) and inaccurate size match in 8.5% (95% CI 6.3–11.2%). Inaccurate size match prolonged operative time ( p = 0.028). Regarding the factors potentially influencing templating accuracy, only gender had a significant influence, with templating being more accurate in men ( p = 0.004). BMI had no influence on accuracy ( p = 0.87). No effect on accuracy was observed for implant type and surgeon experience. Conclusions The accuracy of 2D size templating in TKA is low, even in a specialized ENDOCERT arthroplasty center. The study findings challenge the usefulness of preoperative 2D size templating and highlight the importance of more reliable templating methods. Level of evidence Level III (retrospective observational study).