Summary

A comparison of the accuracy and reproducibility of preoperative component size prediction for total knee arthroplasty between conventional two-dimensional templating (2DT) and CT-based three-dimensional planning (3DP) showed that the 3DP did not allow an improvement in the accuracy and reproducibility over the 2DT.

Abstract

Introduction

Preoperative planning should be reliable and reproducible. Conventionally, preoperative planning in total knee arthroplasty (TKA) has been performed on standard radiographs with acetate overlays of the implants. Previous studies have investigated preoperative templating using acetate overlays. Low intra- and inter-observer reproducibility was also reported in the acetate templating. With the prevalence of digital radiography, opportunities exist for improvement in preoperative planning. The aim of this study was to evaluate the accuracy and reproducibility of preoperative component size prediction for TKA using conventional two-dimensional (2D) templating and computed tomography (CT)-based three-dimensional (3D) planning.

Methods

Eighty-one consecutive patients (62 females and 19 males) with a mean age of 74.8 years who underwent primary unilateral TKA were enrolled in this study. All patients had the same posterior stabilized knee component implanted using the same modified balanced gap technique. The component size was decided using component trials. Preoperatively, both the 2D acetate templating (2DT) and CT-based 3D planning (3DP) were carried out for all patients. In the 2DT, radiographs used were anteroposterior and lateral view of the knee. Plain radiographs were templated against acetate templates. For the 3DP, CT of the whole lower extremity was used. The size and setting position of the femoral and tibial components were simulated with the 3D preoperative planning software. The accuracy was calculated by comparing the predicted size in the 2DT and 3DP with that used at surgery. The chi-square test was used to compare the accuracy of the two procedures. Statistical significance was set at p < 0.05. The intra- and inter-observer reproducibility of the 2DT and 3DP was assessed using the linear weighted kappa (K) coefficient.

Results

In the 2DP, the size of the femoral and tibial component was predicted within ±1 size in 98% (52% exactly) and 100% (62% exactly) of the cases, respectively. In the 3DP, the component size was predicted within ±1 size in 98% (57% exactly) for the femur and 100% (54% exactly) for the tibia. There was no statistical difference in the accuracy between the 2DT and 3DP. In the 2DT, the intra-observer reproducibility for the femoral and tibial component were good (K=0.70) and excellent (K=0.84), respectively. The inter-observer reproducibility for the femoral and tibial component were moderate (K=0.42) and good (K=0.68) in the 2DT. In the 3DP, the intra-observer reproducibility for the femoral and tibial component were excellent (K=0.84) and good (K=0.65), respectively. However, the inter-observer reproducibility were fair (K=0.37 for femur, K=0.36 for tibia) in the 3DP.

Discussion

The 3DP did not allow an improvement in the accuracy of the component size prediction, compared to the 2DT. The intra-observer reproducibility of the 3DP was as good as that of the 2DT. However, the inter-observer reproducibility of the 3DP was lower than that of the 2DT. With this degree of the accuracy and reproducibility, the superiority of the 3DP over the conventional 2DT in predicting implant size was not supported in TKA using the modified balanced gap technique.