Table 2.

Translation (position) and orientation error of the ultrasound-based pedicle screw center relative to the CT-based pedicle screw center

Error type	Healthy model, mean ± SD	Degenerative model, mean ± SD
Translation R (mm)	0.16 ± 0.19	0.55 ± 0.59
Translation A (mm)	−0.01 ± 1.22	−0.35 ± 0.40
Translation S (mm)	0.68 ± 0.38	1.28 ± 1.37
Rotation L-R (degrees)	1.92 ± 1.95	1.60 ± 1.56
Rotation P-A (degrees)	−0.05 ± 0.42	0.81 ± 1.15
Rotation I-S (degrees)	0.40 ± 0.99	−0.79 ± 0.46

R = right; A = anterior; S = superior directions; L-R = left-right; P-A = posteroanterior; I-S = inferosuperior rotation axes.