“Laterograde” access to the epidural space, with placement in the sacral foramina.

The patient is positioned with the back arched comfortably.  Some centers use gel rolls or a Wilson frame, but good results have also been obtained simply supporting the patient with pillows under the abdomen to open up the interlaminar spaces posteriorly. An image intensifier is used to identify the thoracolumbar junction and the L2/3 interspace.  On the anteroposterior (AP) projection, with the image intensifier perpendicular to the patient, the lateral border of the pedicle is identified, and the skin and intended trajectory injected with an appropriate local anesthetic. The Tuohy needle is inserted as shown in Figure 2, angled directly medially with the bevel facing up.  Entry to the epidural space is confirmed with a loss of resistance technique, and then the image intensifier is rotated cranially to provide a steep caudal view angle, which removes the practitioner’s hands from the radiation field for the steering of the electrode.  The bevel of the needle is directed caudally, and a percutaneous electrode is directed caudally into the epidural space (Figure 3).  Either four or eight contact electrodes can be used, depending on the specific application, but in most uses of this technique, the four contact electrodes are preferable.  The electrode is then passed caudally under fluoroscopic guidance with standard techniques for steering epidural electrodes, remaining strictly in the midline until near the foramen of interest (Figures 4, 5, 6).  Just above the foramen of interest, the electrode is directed laterally toward the foramen (Figure 7).  It is important to note that it is undesirable to lodge the electrode within the foramen.  This would be felt as a sudden increase in resistance to the passage of the electrode, as it “wedges” into the space.  This could produce compression of the root with irritation, or extremely low stimulation thresholds that make it difficult to selectively program for sensory effects.

When bilateral electrodes are needed, a similar procedure is used.  The upturned bevels of the two Touhy needles nearly “kiss” in the midline (Figure 8), and then the bevels are turned caudally and the image intensifier is appropriately angled.  The electrodes generally cross in the epidural space and are passed caudally in an analogous fashion to the unilateral placement (Figures 9, 10, 11).
It is important to realize that the terminal pathway from midline to the targeted foramina has the effect of placing the trajectory of the electrode not only near the foramen where the targeted root exits the spinal canal, but places the proximal electrodes over the course of the next two or three more distal roots as they approach their respective foramina.

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