Comparison of analog 2D and digital 3D preoperative templating for predicting implant size in total knee arthroplasty

Figures & data

Figure 1. Conventional 2D templating: anteroposterior view of the knee demonstrating templating of the tibia.

Figure 2. CT-based 3D image model (superimposing the CAD model of the implant) created using KneeCAS (LEXI, Inc., Tokyo, Japan).

Table I.  Kappa coefficients and levels of agreement.

Range of κ	0.0	0.01–0.20	0.21–0.40	0.41–0.60	0.61–0.80	0.81–1.00
Level of agreement	Poor	Slight	Fair	Moderate	Substantial	Almost perfect

Figure 3. Error from implanted size. There was a tendency to underestimate the size in the CT-based 3D procedure.

Table II.  Error from implanted size. The accuracy increased to 98% for templated sizes within one size above or below that actually used for both the 2D procedure and the CT-based 3D procedure.

Error (sizes)	2D template	CT-based 3D template
−3	1 (1%)	0 (0%)
−2	1 (1%)	2 (2%)
−1	28 (28%)	36 (36%)
0	56 (56%)	59 (59%)
1	14 (14%)	3 (3%)
2	0 (0%)	0 (0%)
3	0 (0%)	0 (0%)
Number ±1	98 (98%)	98 (98%)
Out by ±2	2 (2%)	2 (2%)
Total	100	100

Table III.  Weighted kappa coefficients for the 2D procedure and the CT-based 3D procedure.

	κ coefficients	Level of agreement
2D template	0.49	Moderate
CT-based 3D template	0.49	Moderate