Figure 2.

Midline approach to the subarachnoid space. The spinal needle is inserted with a slight cephalad angulation and should advance in the midline without contacting bone (B). If bone is contacted, it may be either the caudad (A) or the cephalad spinous process (C). The needle should be redirected slightly with cephalad and reinserted. If bone is encountered at a shallower depth, the needle is likely walking up the cephalad spinous process. If bone is encountered at a deeper depth, the needle is likely walking down the inferior spinous process. If bone is repeatedly contacted at the same depth, the needle is likely off the midline and walking along the lamina.