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

Abstract

Source: Unger, M. D., et al., Laminotomy for Lumbar Dorsal Root Ganglion Access and Injection in Swine. J. Vis. Exp. (2017)

This video demonstrates a laminotomy procedure in an anesthetized pig to access the lumbar dorsal root ganglion for targeted neurotherapeutic delivery using convection-enhanced delivery.

Protocol

All procedures involving animal models have been reviewed by the local institutional animal care committee and the JoVE veterinary review board.

Single-level Laminotomy

1. Identify the target of laminotomy as the centermost lamina located between and medial to the two zygapophyseal joints.
2. Trace the lamina to its inferior edge, to a point just medial to the contiguous inferior articular process of the caudal zygapophyseal joint.
3. Use a 5-mm Freer elevator or curette to palpate the transition between the caudalmost edge of the lamina and the central canal.
   NOTE: Care is taken not to force the palpating instrument anteriorly as this will contact the dural sac and spinal cord. Note that the spinal cord in swine extends past the lumbar spine. An intervertebral disc rongeur can be used to remove additional soft tissue overlying this area to facilitate palpation.
4. Use a 2-mm up-biting, 45-degree Kerrison rongeur to extract bone in a piece-wise 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.
5. Use angled bone rongeurs to assist with bone removal. Leave the inferior articular process that was connected to the lamina in place until the laminotomy is largely completed.
6. Confirm that the inferior articular process is freely mobile and attached only by the zygapophyseal joint capsule. Incise the capsule using a #15 or #11 blade.
7. Remove the inferior articular process in a piece-wise fashion, but leave the adjoining superior articular process intact.
   NOTE: As the laminotomy is completed, hemostasis is performed with bipolar electrosurgery. Monopolar electrosurgery is not used because of the proximity of neural structures. Bone wax can be placed along sites of bleeding from exposed bone, and absorbable gelatin sponges can be used to obtain hemostasis near soft tissue. Cottonoid is a helpful tool to wick serous fluid and blood away from the dissection.

Dissection of Dorsal Root Ganglion (DRG)

1. Evacuate the epidural fat in a piece-wise fashion from superficial to deep beginning medially and proceeding laterally. Remove fat by gentle dissection using bipolar forceps and suction with 6 - 10 French Frazier suction tips.
   NOTE: Loupe magnification or the use of a dissecting microscope is helpful in providing the level of detail needed to safely evacuate the epidural fat and achieve meticulous hemostasis of the epidural venous plexus using bipolar electrosurgery.
2. Identify the dural sac along the midline running in a superoinferior direction parallel to the axis of the skin incision. Remove epidural fat along the dural sac until the dural sac can be seen to give rise to the dural nerve root sleeve.
3. Trace the dural sleeve laterally and inferiorly by epidural fat evacuation, drguntil it is seen to enlarge around the DRG (Dorsal Root Ganglion).
   NOTE: Identify the DRG for its oval shape and yellow-to-orange color. At the mid-lumbar spine, the DRG is typically 4 - 6 mm in size, longest in the medial to lateral direction, and located directly inferior or 2 - 3 mm medial to its respective pedicle. A blunt, right-angled nerve hook can be used to gently palpate for the pedicle.
4. Evacuate epidural fat laterally, past the DRG, until the adjoining spinal nerve is seen.
   NOTE: If durotomy occurs, repair it by watertight closure using 6-0 nylon suture and smooth micro needle driver in a simple running stitch.

Injection of Dorsal Root Ganglion

1. Use a 22-gauge spinal needle to guide the trajectory of a 32-gauge convection-enhanced delivery (CED) needle. Puncture the 22-gauge guide needle through the skin and paraspinal muscles.
   NOTE: The CED needle is designed to achieve fluid convection in tissue, also known as bulk flow, due to pressure gradients.
2. Aim the guide needle along a trajectory that approximates the longitudinal axis of the DRG and results in the needle tip emerging from the lateral paraspinal wall of the dissection field.
3. Fine-tune the needle path until the needle lumen aligns with the center of the DRG.
   NOTE: The guide needle should never be allowed to contact the DRG.
4. Draw up sterile injectate into a sterile syringe and connect the syringe to the sterile infusion tubing.
5. Secure the tubing to the CED needle and hand the syringe out of the sterile field. Connect the syringe to a programmable syringe pump.
   NOTE: Tubing is prepared to a length of 5 feet to ensure that sterility and mobility are maintained. Also, it is of paramount importance that no air bubbles be introduced into solution.
6. Advance the injectate until the expression is seen from the CED needle tip.
7. Place the CED needle within the guide needle lumen and slowly advance the CED needle until it emerges from the guide needle tip. Ensure that the DRG is not punctured during needle alignment.
8. Fine-tune the guide needle position along the long axis of its trajectory to determine the final location of the CED tip.
9. Secure the guide needle and CED needle together using interlocking needle hubs once depth and alignment of the guide and CED needles is achieved.
10. Confirm that all injection apparatus connections are fully secured, including the guide needle, CED needle, and connected tubing loaded with injectate.
11. Advance the guide needle along its long axis to approximate the CED needle tip and DRG.
12. Puncture the DRG with the CED needle tip.
13. Submerge the CED needle tip into the three-dimensional center of the DRG.
    NOTE: Because the DRG is a three-dimensional structure of variable size and shape, DRG exposure must be complete in order to accurately place the CED needle tip at the true center of the DRG. The true DRG center is located at the intersection of its three anatomical axes, namely, the anterior to posterior, lateral to medial, and superior to inferior axes.
14. Deliver 100 μL of injectate by CED using a graduated rate and volume of 3 steps.
15. Deliver 4 μl at 2 μL/min for the first step. Deliver 8 μL at 4 μL/min for the second step. Deliver 88 μL at 8 μL/min for the third and final step.
    NOTE: Allow a 3-min pause between steps and after the final step to allow for pressure equilibration.
16. Withdraw the injection apparatus after the final injection step and 3-min pause along its long axis in a smooth, gentle motion.
    NOTE: For injected solutions that are colorless, colored dye is included in the solution at a concentration of 0.1% weight/volume to assist in visual assessment of injectate distribution. Also, the vital dye 4',6-diamidino-2-phenylindole (DAPI) is included in solution at a concentration of 0.25 μg/μL when the study design requires histologic assessment of injectate distribution.

Closure

1. Apply 3 rounds of warm saline irrigation to the surgical site prior to closure to mobilize and flush the site of debris, i.e., bone fragments. Use suction to recover the saline and debris.
   NOTE: Meticulous hemostasis is ensured when irrigation remains clear. Hemostatic agents (gelatin sponge) and cottonoid are removed at this time. Ensure that all materials and instruments have been cleared from the incision site prior to closure.
2. Use a 3-layered technique for closure.
3. Suture the thoracolumbar fascia using 0 suture in a simple, interrupted, noninverted fashion. Place a stitch every 5 - 8 mm to achieve a watertight closure.
4. Suture the subcutaneous tissue using 2-0 suture in a simple, interrupted, inverted fashion with a stitch placed every 5- to 8-mm to achieve adequate strength.
5. Close the skin using a 0 suture in a simple, running, or interrupted fashion.
6. Use a needle counter to ensure that no sharps are unaccounted for.
7. Irrigate the skin with saline, dry the skin, and place adhesive bandage strips perpendicular to the incision.
8. Place gauze on top of the bandage strips and attach a final adhesive antimicrobial incise drape.

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Disposable suction canister and tubing	Medline	DYND44703H	-
Button switch electrosurgical monopolar pencil	Medtronic	E2450H	-
15 blade	Miltex	4-315	-
11 blade	Miltex	4-311	-
4x4 surgical gauze	Dynarex	3262	-
Freer elevator, 5 mm	Medline	MDS4641518F	-
Bone wax	Ethicon	W31G	-
Spurling intervertebral disc rongeur, 3 mm	Sklar	42-2852	-
Spurling 45-degree, up-biting Kerrison rongeur, 2 mm	Medline	MDS4052802	-
Leksell angled rongeur, 2 mm	Sklar	40-4097	-
Frazier suction tip, 6 Fr	Sklar	50-2006	-
Frazier suction tip, 10 Fr	Sklar	50-2010	-
Dandy blunt right angle nerve hook	Medline	MDS4005220	-
Nylon suture, 6-0	Ethicon	697G	-
22 gauge Quinke point spinal needle	Halyard Health	18397	-
Polyethylene tubing, 5 feet	Scientific Commodities	BB31695-PE/05	-
DAPI	Sigma-Aldrich	D9542	-
Vicryl suture, 0	Ethicon	J603H	-
Vicryl suture, 2-0	Ethicon	J317H	-
Needle counter	Medline	NC20FBRGS	-
Steri-strip skin closure, 1/2x4 inch	3M	R1547	-