# Table 3 Comparisons between 2D and 3D measurements

3D Mean value (SD) 2D Mean value (SD) Error (%)* P-value R a** b**
Sagittal Plane Tibia Part
TiAL (mm) 28.41 (2.62) 29.35 (2.75) 3.28 <0.001 1.00 0.95 0.39
TiSR (mm) 29.07 (8.30) 30.04 (8.66) 3.32 <0.001 1.00 0.96 0.25
APG (mm) 3.85 (2.65) 3.98 (2.74) 3.18 <0.001 1.00 0.97 -0.01
APA (deg) 7.86 (5.40) 7.86 (5.40) 0.00 0.86 1.00 1.00 0.00
MTiTh (mm) 42.44 (4.83) 44.64 (3.07) 5.17 0.10 0.54 0.72 10.22
MDA (mm) 10.21 (2.47) 12.68 (2.99) 24.20 <0.001 0.82 0.81 0.16
MDV (mm) 3.15 (1.64) 3.11 (1.89) -1.24 0.11 0.37 0.44 2.01
Talus Part
TaAL (mm) 33.55 (4.54) 31.80 (5.29) -5.22 <0.001 0.81 0.58 15.13
TaR (mm) 20.57 (2.78) 21.20 (3.13) 3.05 0.57 0.09 0.16 17.06
Frontal Plane Tibia part
TiW (mm) 32.84 (2.72) 33.95 (2.69) 3.38 <0.001 0.86 0.85 3.96
MalW (mm) 62.60 (3.69) 63.73 (3.83) 1.80 <0.001 1.00 0.97 0.95
MLATi (deg) 12.59 (3.08) 12.61 (3.08) 0.13 0.63 0.99 1.00 -0.03
Talus part
TaW (mm) 19.89 (4.45) 20.02 (3.82) 0.68 0.34 1.00 0.92 1.89
MLATa (deg) 2.31 (3.67) 2.06 (3.20) -10.87 0.01 0.99 1.07 0.04
1. *Error = 100% × (2D - 3D)/3D.
2. **Linear Regression: (3D) = a × (2D) + b.
3. Mean values and standard deviations of 2D and 3D measurements, and the mean errors of 2D measurements as percentages of 3D measurements. Negative error values indicate that the parameter measured from 2D images under-estimated those measured from 3D CT data. Pearson’s correlation coefficients and P-values of comparisons between 2D and 3D measurements using a paired t-test are also given. The coefficients (a, b) corresponding to the linear regression analysis on the 2D and 3D measurements are listed.