Fig. 8.

Medial branch block under CT guidance. a: L4–5 level; b: L5-S1 level. c, d: Diffusion of contrast media prior to anesthetic injection confirming optimal needle tip placement (white arrows). Needle tip at the target point at injection should be placed at the middle of the base of the transverse process at its junction with the superior process at the L4–5 level. An analogous target point should be used at the L5-S1 level midway between the upper end and middle of the ala of the sacrum (white stars). Vr: ventral ramus. Dr: Dorsal ramus. m: medial branch. i: intermediate branch. l: lateral branch