Surface Landmarks

Surface landmarks are follows: A line is drawn between the posterior
superior iliac spine (PSIS) and the lowest point of the ischial tubero-
sity (IT). Both of these points are usually easily identified. The needle
insertion point lies three fingers breadth inferior to the PSIS on this
line (6cm). This point is just below the posterior inferior iliac spine,
which usually cannot be palpated (Figure 3).

Needle Orientation

The needle is connected to a nerve stimulator. For a single shot, the needle is directed perpendicular to the skin in all planes and strictly horizontal. It is important not to direct the needle medially (Figure A). With a continuous block technique, the puncture site is the same; however, the needle is directed 10° more caudally to facilitate insertion of the catheter (Figure B and C).