Fig. 1.

Cross-sectional MRI scan of lumbar pedicle: Successful puncture at the Max-angle. Line M: Anteroposterior midline of the vertebrae; A: the intersection point of Line M and the vertebral anterior edge; P: the intersection point of Line M and the vertebral posterior edge; T: the anterior trisection point of Line AP; ∠EIP: Puncture Max-angle; Line EI was used to simulate the puncture device which was 3.5 mm in diameter; the inner edge of Line EI was tangential to the medial wall of the pedicle, and the outer edge of Line EI was tangential to the lateral wall. In Fig. 1, the Puncture Success Value = 100*AI/AP > 34, and it was considered a successful puncture