Full Endoscopic Transforaminal Thoracic Discectomy Operative Technique

The protocol follows the human care guidelines of the Houston Methodist Hospital Institutional Review Board. A single patient was included in the study. Inclusion criteria: patient aged >18 years of age with a thoracic disc herniation causing symptoms of myelopathy and/or radiculopathy, a patient without medical comorbidities prohibiting 3-4 h of general anesthesia or prone positioning. Informed consent was obtained from the patient prior to participation in the study.

1. Preoperative planning

1. Obtain a preoperative MRI to evaluate the morphology of the disc herniation.
2. Obtain a preoperative CT scan to evaluate for calcification of the disc herniation as well as full understanding of local spinal and rib anatomy. A CT will also be helpful for the identification of localizing anatomy at both the index and adjacent levels (i.e., adjacent level unique osteophytes).
3. If transitional anatomy is present or if the operative level cannot be safely and accurately localized with the preoperative MRI and CT, obtain preoperative whole spine X-rays (36-inch films) to evaluate for transitional anatomy and improve the accuracy of intraoperative localization.
   NOTE: The placement of an intrapedicular or intravertebral localization marker (e.g., metallic bead or coil) pre-operatively by interventional radiology may be considered to avoid wrong-level surgery.

2. Surgical details

1. If the procedure is to be performed under general anesthesia, utilize total intravenous anesthesia (TIVA) to facilitate neurophysiologic monitoring and, in cases of spinal cord compression and/or myelopathy, utilize invasive arterial blood pressure monitoring to maintain a mean arterial pressure >85.
   1. If the procedure is to be performed under local anesthesia with conscious sedation, neurophysiological monitoring and invasive arterial blood pressure monitoring are not required. Techniques for both local anesthesia with conscious sedation and general anesthesia administration for endoscopic spine surgery have been described in detail elsewhere¹⁵.
2. Place the patient prone on a radiolucent spinal surgery bed. For lesions above T7/8, tuck the patient's arms at the side to allow for lateral fluoroscopic imaging (see Table of Materials).
3. Sterilize/prepare the surgical area with a surgical prep and drape the surgical field with sterile drapes.
4. Localize the operative level with fluoroscopy and make a mark on the skin at the operative level.
   1. Using fluoroscopy in an anterior-posterior (AP) view, count up from the lowest rib for lower thoracic operative levels – or count down from the highest rib for higher thoracic operative levels – to localize the operative level.
5. Place a shallow subdermal needle at the caudal pedicle of interest to serve as a reference marker for the lateral portion of the targeting.
6. Draw a trajectory line on the AP view, targeting the area of interest.
   NOTE: The trajectory for the approach of a thoracic disc herniation typically projects from a cranial to caudal and lateral to medial direction in order to avoid the exiting nerve root within the neural foramen at the level of interest.
7. Mark the distance from the midline to the entry point for the endoscope, which is generally 6-8 cm off the midline in the thoracic spine.
8. Make a 1 cm incision at the skin entry point using a scalpel.
9. Using lateral view fluoroscopy, advance a targeting biopsy needle (see Table of Materials) toward the index facet joint. Due to the approach angle dorsal to the rib apex and the medial to lateral downward sloped facet joints in the thoracic spine, the biopsy needle will likely land on the lateral aspect of the inferior articulating facet.
10. Once the biopsy needle is docked on the facet joint at the index level, advance the needle into the facet joint several millimeters to ensure adequate engagement and securement.
11. Exchange the biopsy needle for a guidewire (see Table of Materials) and return the fluoroscopy to the AP view.
12. Under AP fluoroscopy, place sequential dilators over the guidewire and ream the lateral aspect of the facet joint (superior articulating process) to enlarge the neural foramen, taking care not to cross the medial pedicular line (i.e., the lateral boundary of the canal).
    NOTE: Sequential dilators are a set of three progressively large tubular retractors that dilate soft tissue surrounding the biopsy needle/K-wire to the caliber required for the introduction of an endoscopic cannula.
13. Once the reaming is complete, place the endoscopic cannula (inner diameter 6.5 mm; outer diameter 7.5 mm, see Table of Materials) over the largest dilator and advance the cannula down to the neural foramen.
14. Remove the guidewire and dilators, leaving the endoscopic cannula in place.
15. Insert the endoscope into the endoscopic cannula.
16. Using a 3.5 mm diamond burr on an endoscopic drill (see Table of Materials), drill away a portion of the remaining superior articulating process in order to allow for visualization into the lateral recess of the spinal canal.
17. Use the endoscopic dissector probe to identify the lateral recess, disc space, disc herniation, and thecal sac (Figure 1).
18. Remove any easily accessible free fragments of herniated disc material with grasping forceps.
19. For large and/or calcified disc herniations in particular, use the 3.5 mm diamond burr to drill a small cavity into the vertebral body cranial, caudal and ventral to the disc herniation (i.e., a limited corpectomy) to facilitate the manipulation of disc herniation fragments away from the spinal cord. Cut the annulus/posterior longitudinal ligament above and below the disc herniation in order to free the disc herniation prior to mobilizing and removing it.
    NOTE: As decompression progresses, the thecal sac will drop into view. The thecal sac will be seen to pulsate when adequate decompression is achieved. The endpoint of the surgery is when the thecal sac is visualized in anatomic configuration, pulsating.
20. After the disc herniation has been removed and the spinal cord is decompressed, withdraw the endoscopic cannula and close the 1 cm skin incision with deep dermal buried 3-0 monocryl sutures (see Table of Materials). Seal the skin closure with a dermal glue adhesive.

3. Postoperative care

NOTE: If the patient did not have severe neurological deficits/functional deficits pre-operatively and their pain is well controlled, they are discharged home the same day.

1. Discharge patients with Acetaminophen 300 – Codeine 30 (1-2 tablets to be taken every 4-6 h PRN pain) and methocarbamol 500 mg (1 tablet every 6-8 h PRN muscle spasms).
   NOTE: Patients with severe preoperative neurologic deficits may be evaluated for discharge to inpatient rehabilitation.
2. Instruct patients to keep the incision dry for one day, after which they can shower normally.
3. Instruct patients not to submerge the wound in water for at least 6 weeks.
4. Instruct patients to avoid strenuous activities and minimize bending, lifting greater than 10 pounds, or twisting of the torso for 6 weeks postoperatively.