5.5. Patient Positioning and Portal Placement
@ProfFishchenkoIn my practice, I position the patient prone on a Wilson frame to provide flexion of the lumbar spine. We coordinate the position of the head and trunk with the anesthesiologist to maintain ventilation and venous drainage. We keep the head in a neutral position and avoid pressure on the eyes and abdomen. The anesthesiologist determines the target blood pressure individually, taking baseline pressure, comorbidities, and organ perfusion into account. In my practice, a systolic pressure of approximately 100 mmHg may serve as a guide when clinically appropriate. We place soft cushions under the knees and lower legs.
Before incision, we confirm the operative level with the C-arm, correlating vertebral numbering with the preoperative images. We obtain an anteroposterior image. We use a lateral projection whenever there is uncertainty about the level or instrument depth, particularly in the presence of lumbarization, sacralization, or hyperlordosis. If needed, we repeat lateral imaging during trocar and dilator placement.
Endoscopic portal
In my practice, I hold the endoscope in my left hand and the instruments in my right. For a left-sided approach, we use the cranial portal for the endoscope and the caudal portal for instruments; for a right-sided approach, their roles are reversed. Details of portal positioning at L5–S1 are described separately in sections 5.8 and 5.9.
I prefer longitudinal skin incisions. We anticipate the possibility of conversion to microdiscectomy before surgery, particularly during training: longitudinal incisions are easier to join if needed.
We first create the endoscopic portal. Using a pointed scalpel, we incise the skin, subcutaneous fat, and outer layer of the fascia of the longissimus muscle. We approach at an angle of 20–40° toward the base of the transverse process.
We introduce the first and second dilators through the opening, touching the junction between the lamina and the base of the transverse process. We dissect the muscles using the dilators or dedicated muscle dissectors. We identify the bony landmarks by palpation: the dorsal aspect of the base of the transverse process, the lateral aspect of the base of the superior articular process, the pars interarticularis (isthmus), the dorsolateral aspect of the base of the inferior articular process, and the dorsolateral aspect of the superior articular process.
We carefully identify the posterolateral surface of the posterior elements of the adjacent vertebrae without advancing deeply into the paravertebral space. We remove the dilators and introduce the trocar into the portal tract created. We again palpate the bone and the slope between the dorsal aspect of the base of the transverse process and the lateral aspect of the base of the superior articular process.
Working portal
Using a pointed scalpel, we incise the skin, subcutaneous fat, and outer layer of the thoracolumbar fascia (fascia thoracolumbalis) at an angle of 20–40° toward the base of the transverse process. We rotate the scalpel 90° and make an additional transverse fascial incision. This creates a cruciate incision in the thoracolumbar fascia to improve fluid outflow.
We sequentially introduce three dilators through the opening. We again palpate the bone: the dorsal aspect of the base of the transverse process, the lateral aspect of the base of the superior articular process of the lower vertebra, and the lateral aspect of the inferior articular process of the upper vertebra. We bring the dilators together with the trocar passed through the endoscopic portal and confirm “metal-to-metal” contact by touch. The meeting point is the isthmus of the upper vertebra.
At this stage, we obtain a lateral radiograph if needed.
We replace the trocar stylet with the endoscope and camera. We replace the dilators with an RF electrode with a 5 mm working tip. We confirm its position under endoscopic video visualization. The meeting point is the isthmus of the upper vertebra.
Bony landmarks must be identified by touch and confirmed visually. Bone provides the landmark and the safest area. Reliable orientation is impossible without visualization of bone.
If instrument positioning is uncertain or bony landmarks are lost, we obtain anteroposterior and lateral imaging before continuing.
Dissection and exposure of landmarks
We then use the RF electrode in ablation mode to expose the distal edge of the transverse process of the cranial vertebra, the isthmus, the inferior and superior articular processes, and the proximal portion of the transverse process of the caudal vertebra. After identifying the bony landmarks, we remove excess soft tissue lateral to these structures using a shaver (Tomcat, Aggressive Plus, 5 mm) or continue ablation with the RF electrode.
At this stage, we clearly visualize the following bony landmarks:
- the distal edge of the transverse process of the cranial vertebra;
- the isthmus;
- the inferior and superior articular processes;
- the proximal portion of the transverse process of the caudal vertebra.
We advance deeper while carefully exposing the superior articular process of the caudal vertebra and its distal portion.
If only muscle tissue is visible in the endoscopic field and the pars interarticularis and superior articular process cannot be identified, the endoscope and working instruments may be positioned too far laterally. Their position relative to the bony landmarks should be confirmed before further advancement [6].
Caution: Loss of orientation
During the initial stages of learning the technique, limited experience may lead to unintentional advancement deeper than the intervertebral foramen and ventrally along the vertebral body. This may injure a segmental artery and cause excessive fluid accumulation in the retroperitoneal space.
If orientation is lost, we do not continue advancing blindly: we clarify instrument positioning using anteroposterior and lateral imaging.
With limited experience, advancement may occur predominantly in the dorsal → ventral direction rather than the lateral → medial direction.
References
1. 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.
2. 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.
3. Park JH, Jung JT, Lee SJ. How I do it: L5/S1 foraminal stenosis and far-lateral lumbar disc herniation with unilateral bi-portal endoscopy. Acta Neurochir (Wien). 2018;160(10):1899–1903. doi:10.1007/s00701-018-3630-9.
4. Saugel B, Fletcher N, Gan TJ, et al; POQI XI Workgroup. PeriOperative Quality Initiative (POQI) international consensus statement on perioperative arterial pressure management. Br J Anaesth. 2024;133(2):264–276. doi:10.1016/j.bja.2024.04.046.
5. American Society of Anesthesiologists Task Force on Perioperative Visual Loss, North American Neuro-Ophthalmology Society, Society for Neuroscience in Anesthesiology and Critical Care. Practice advisory for perioperative visual loss associated with spine surgery 2019. Anesthesiology. 2019;130(1):12–30. doi:10.1097/ALN.0000000000002503.
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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