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Table 1 Summary of computed tomography grading criteria

From: The technical feasibility and preliminary results of minimally invasive endoscopic-TLIF based on electromagnetic navigation: a case series

Grade Accuracy of PPSP according to Neo et al. [15]
0 No deviation; the screw was contained in the pedicle
1 Deviation < 2 mm (i.e., less than half of the screw diameter)
2 Deviation > 2 and < 4 mm
3 Deviation > 4 mm (i.e., complete deviation)