Laminotomy for Targeted Injection into the Lumbar Dorsal Root Ganglion in a Pig Model

Begin with an anesthetized pig with three lumbar vertebrae surgically exposed.

Identify the lamina, a flat bone between the spinous process and facet joints.

Trace it toward the spinal canal while avoiding pressure on the dural sac, the spinal cord’s protective covering.

Remove the lamina in small pieces.

Cut the underneath membrane to expose the fat.

Remove the lower joint to improve access, keeping the upper part intact to maintain spinal stability.

Extract fat to expose the dural sac, dorsal root ganglion (DRG), and nearby spinal nerves.

Identify the DRG, which transmits sensory and pain signals, then insert a convection-enhanced delivery (CED) needle connected to an infusion system into its center.

The CED needle uniformly delivers the dye-loaded solution through positive pressure while minimizing leakage.

This targeted injection enables precise neurotherapeutic delivery to the lumbar DRG.

Finally, withdraw the needle and close the surgical site.

With care, use a five-millimeter Freer elevator or curette to palpate the transition between the caudal-most edge of the lamina and central canal.

Do not force the elevator anterior. Next, using rongeurs, extract bone in a piecewise fashion. Remove bone along the base of the spinous process superiorly to a level just caudal to the caudal surface of the pedicle and out laterally to its full extent.

Expose the smooth shiny periosteum in full. Cut with a number-11 blade and expose epidural fat. Leave the inferior articular process that was connected to the lamina in place for most of the laminotomy.

Then, remove the inferior articular process in a piecewise fashion, but leave the adjoining superior articular process intact. Now, dissect the DRG with the aid of loop magnification or a dissecting microscope. First, evacuate the epidural fat in a piecewise fashion beginning medially and proceeding laterally.

Make a gentle dissection with bipolar forceps and suction via six to 10 French Frazier suction tips. Next, identify the dural sac along the midline running in a superior inferior direction parallel to the axis of the skin incision. Then, remove epidural fat along the dural sac until the dural sac can be seen to give rise to the dural nerve root sleeve.

Now, continuing the epidural fat evacuation, trace the dural sleeve laterally and inferiorly until it is seen to enlarge around the DRG. The DRG is oval and yellow-orange about four to six millimeters wide. Proceed laterally with the fat removal past the DRG until the adjoining spinal nerve is seen.

Use a 22-gauge spinal needle to guide the trajectory of a 32-gauge CED needle. Puncture the guide needle through the skin and paraspinal muscles. Very carefully, aim the guide needle along a trajectory that approximates the longitudinal access of the DRG.

Gradually advance the guide needle until the tip emerges from the lateral paraspinal wall of the dissection field. Then, advance the guide needle along its long axis to approximate the CED needle tip to the DRG. Now, puncture the DRG with the CED needle tip and submerse the tip into the three-dimensional center of the DRG.

It is critical to again consider the unique size and shape of the exposed DRG. The goal is to achieve a smooth puncture and submerge the needle tip to reach the DRG's three-dimensional center without overshooting or missing your mark. Now, deliver 100 microliters of injectate by CED at a graduated rate over the next 24 minutes.

After the last step, a three-minute rest, withdraw the injection apparatus along its long axis in a smooth, gentle motion. Finally, close the surgical site as described in the text protocol. After closure, clean the skin and apply adhesive bandage strips perpendicular to the incision followed by gauze, and then an adhesive antimicrobial drape.