Figure 1

Medial and lateral deviations of the screw classified according to the modified classification. Grade 0, no deviation and the screw was contained in the pedicle. Grade 1, deviation less than 1 mm (i.e., less than half of the screw diameter). Grade 2, deviation more than 1 mm and less than 2 mm (i.e., less than half of the screw diameter). Grade 3, deviation more than 2 mm and the direction of misplacement was medial, lateral, superior, or inferior. Grades 2 and 3 were considered critical deviations.