Fig. 3

Diagrams of four-stepped osteotomy. The osteotomy was performed in four different directions to cleft the outer and inner cortex of the vertebral body on each side, and eight holes were made in the anterior cortex by projecting the nail tip to fragile the cortex. a The osteotome was hammered through the previous pedicle screw trajectory until the anterior edge of the osteotome touched the anterior cortex of vertebral body, an inner nail was inserted to form a hole on the anterior cortex. b A diverged direction of osteotomy split the outer cortex of the pedicle and vertebral body. c Osteotomy was performed to cleft the inner cortex of pedicle and medial part of vertebral body. d Osteotome was hammered at 40~45° to cleft the posterior wall of vertebral body