A conventional method for determining of needle entry on preoperative magnetic resonance image and under fluoroscopy. (A) (Left) Using picture archiving and communication system drawing tool, an angle and the distance from the midline to the skin of the needle entry point are determined preoperatively over an axial film of MRI. The first line is drawn from the skin of the midline via the spinous process to the posterior 1/3 of the intervertebral disc (IVD), and the second line is drawn from the posterior 1/3 of the IVD passing through the herniated disc to the skin. (Right) A line is drawn from the skin to the posterior IVD via the herniated nucleus pulposus on the sagittal view. (B) A conventional method for determining needle entry: (Left) A K-wire is placed between the upper and lower endplate and a line is drawn over the K-wire. The midline is marked between the adjacent spinous processes under fluoroscope. The distance from the midline, which has already been measured from preoperative MRI, is marked using a ruler. (Right) It is important to adjust the lateral view so that both the upper and lower endplate of the targeted disc are clearly seen. It is better to first place a needle to touch the upper endplate for upward migration or to touch the lower endplate for downward migration. According to up- or down-migration, another K-wire is placed on the lateral view. The meeting point of the 2 K-wires is the destination of needle entry.
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