8.4. Nerve Identification
@ProfFishchenkoPrevious section: Surgical Approach
After initial hemostasis, we identify the lateral surface and tip of the superior articular process (SAP). It contributes to segmental stability, so excessive resection may cause instability.
Calcification of the foraminal ligament
Before resecting the tip of the superior articular process with a chisel, preoperative imaging should be assessed for calcification of the foraminal ligament. If the ligament is calcified, the nerve root may be injured during this stage of the procedure [6].
In my practice, I use a 5 mm-wide endoscopic chisel; in this technique, this dimension is the limiting reference for resection of the SAP tip. We measure 5 mm and position the chisel perpendicular to the superior articular process, at 45° to both the coronal and sagittal planes. The aim is to separate the tip as a single fragment under endoscopic video guidance. If controlled removal as one fragment is not possible, we divide it into smaller pieces. The base of the SAP tip is triangular in the axial plane.
We remove the separated tip with upturned rongeurs under direct visual guidance. If ligaments retain the fragment, we release only clearly visible attachments while protecting the exiting nerve root. If necessary, we divide the fragment into smaller pieces for controlled removal. We do not push it medially into the intervertebral foramen.
After removing the tip, we visualize the exiting portion of the nerve, which is covered by a ligament laterally in the extraforaminal region. Using reverse 3 mm Kerrison rongeurs, we remove the ligament over a length of approximately 10 mm to expose the nerve. We control bleeding from the radicular vessels if necessary.
After identifying the nerve, we trace its course and identify additional causes of compression: bony overgrowth at the distal portion of the transverse process, subpedicular osteophytes, a disc component, and bony spurs of the vertebral endplates.
Resection of Bony Overgrowth at the Distal Transverse Process
The transverse process may have a substantial anteroposterior thickness of up to 1–1.5 cm. Full-thickness resection is unnecessary. We identify only the areas closely adjacent to the nerve. We prepare a working surface for the chisel with a burr, then perform resection. In my practice, I use a 1–2 mm gap between the nerve and the transverse process as a reference, approximately the width of the side of the chisel.
Subpedicular Osteophytes
In foraminal stenosis, the nerve may be compressed where it emerges from beneath the vertebral pedicle. In these cases, we partially resect the pedicle for decompression. We prepare a surface with a ball burr for subsequent chisel work. In my practice, I use an upward-curved 30° chisel here. We remove the bone gradually in fragments 1–2 mm wide. We retrieve the fragments with fine upturned rongeurs. If a fragment cannot be grasped, we mobilize it toward ourselves with a curette under visual guidance and remove it with rongeurs.
Caution: Dorsal Root Ganglion
The dorsal root ganglion (DRG) lies where the nerve exits the intervertebral foramen. Even minor injury to it may cause prolonged neuropathic pain.
Bony Spurs of the Vertebral Endplates
Caudal to the nerve, we identify the intervertebral disc. To resect osteophytes sparingly, we expose them from the disc side. Using an endoscopic annulotomy knife (Indian knife), we create an opening in the annulus fibrosus and enlarge it with Kerrison rongeurs. From the disc side, we expose the bony spurs of the cranial vertebral endplate using the RF electrode in ablation mode at a low power setting.
In my own technique, I gently displace the nerve cranially with a straight chisel, using the chisel as a retractor. I position the same chisel as perpendicular to the osteophyte as possible and continue holding the nerve with it while knocking off the osteophyte. I do not use a separate retractor at this stage. I remove the bone fragments with rongeurs under endoscopic video guidance.
After decompressing the nerve, we perform meticulous hemostasis. We coagulate bleeding vessels near the nerve under direct visual guidance, with continuous irrigation and free outflow. In my practice, we use COAG 2 on the BONSS ARS600 scale near neural structures — this is a setting level, not a value in watts. We direct the active surface of the RF electrode only toward bleeding tissue; we do not allow an activated electrode to contact the nerve. We control bleeding from bone with bone wax.
Under endoscopic video guidance, we introduce a No. 15 drain into the created cavity through the working portal, keeping it away from the exposed nerve. We secure the drain to the skin. In my practice, I remove it the next day, or immediately if neural structures are irritated. Irritation may result either from contact between the drain and the nerve or from the negative pressure it creates. We do not place a drain after an intraoperative dural injury or during BELIF/UBE-LIF.
We close each skin incision with a single interrupted Vicryl 2-0 suture.
References
1. Choi DJ, Kim JE, Jung JT, et al. Biportal endoscopic spine surgery for various foraminal lesions at the lumbosacral lesion. Asian Spine J. 2018;12(3):569–573. doi:10.4184/asj.2018.12.3.569.
2. Ahn JS, Lee HJ, Choi DJ, Lee KY, Hwang SJ. Extraforaminal approach of biportal endoscopic spinal surgery: a new endoscopic technique for transforaminal decompression and discectomy. J Neurosurg Spine. 2018;28(5):492–498. doi:10.3171/2017.8.SPINE17771.
3. Kim JE, Choi DJ, Park EJ. Clinical and radiological outcomes of foraminal decompression using unilateral biportal endoscopic spine surgery for lumbar foraminal stenosis. Clin Orthop Surg. 2018;10(4):439–447. doi:10.4055/cios.2018.10.4.439.
4. Heo DH, Park DY, Hong YH, Kim D, Kim JS. Temperature change of epidural space by radiofrequency use in biportal endoscopic lumbar surgery: safety evaluation of radiofrequency. Eur Spine J. 2023;32(8):2769–2775. doi:10.1007/s00586-023-07719-z.
5. Ahn DK, Lee JS, Shin WS, Kim S, Jung J. Postoperative spinal epidural hematoma in a biportal endoscopic spine surgery. Medicine (Baltimore). 2021;100(6):e24685. doi:10.1097/MD.0000000000024685.
6. Park M.K., Heo D.H. Biportal Endoscopic Paraspinal Approach for Foraminal and Extraforaminal Disc Herniations. In: Advanced Techniques of Endoscopic Lumbar Spine Surgery. Springer; 2020. P. 91–99; relevant passage: p. 98. Book chapter.
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