For nerve stimulator-guided psoas compartment block, the needle insertion site can be localized in one of two ways:
- In method 1, the needle is inserted 4 cm lateral to the midline along a line drawn from the iliac crest to the L4 spinous processes in the midline of the back.
- In method 2, the needle insertion site is found by first drawing a line (line 1) connecting the iliac crests. The PSIS is identified and the lumbar spinous processes are marked. A second line (line 2) is drawn through the PSIS parallel to a third line (line 3) connecting the spinous processes. The needle is inserted 1 cm cephalad to the junction of the lateral third and medial two-thirds of a line between the lines 2 and 3 at the level of L4.
