Indications and contraindications are very similar to conventional microscopic decompression surgery. The FOS lesion combined with foraminal stenosis at the L5/S1 level and the recurrent FOS can also be treated by this technique. However, grade 2 or higher spondylolisthesis and segmental instability are contraindicated in this technique.
Special Instruments
A zero-degree endoscope is most commonly used in UBE surgery. A radiofrequency (Arthrocare®) probe is essential to control intraoperative bleeding. The arthroscopic drill system with saline drain portal and high-speed electrical drill is commonly used to drill out the bony structure (Fig. 11.2). The scope-retractor is also useful in preventing nerve root damage. The curved Kerrison punch is very useful to decompress the foraminal lesion. All conventional surgical instruments are available in this technique (Fig. 11.3).
Anesthesia and Position
Both endotracheal general anesthesia and epidural anesthesia are available in this surgery. The authors prefer epidural anesthesia because it is a less invasive procedure and less loading on cardiopulmonary function than general anesthesia. The patient is always placed on a Wilson frame in the prone position. In addition, less lumbar lordosis using elevation of the Wilson frame can make the operation comfortable because this induces the widening of the foraminal area and reduces intra-abdominal pressure. Compression stockings prevent thrombosis in the lower extremities during the surgery. A Foley catheter is usually inserted to check perioperative urine output (Fig. 11.4).
Surgical Steps
- Identify the location of two portals and make portals (left side approach) (Fig. 11.5)
Setting the true anteroposterior (A-P) image under fluoroscopic guidance is the first step for this surgery. Especially, the L5-S1 level has the most lordotic angle; it is very important to apply the fluoroscopic device at a cranial angle to get the accurate A-P image (Fig. 11.6). The UBE surgery utilizes two portals: one for the endoscope and the other for surgical instruments. The L5 and S1 pedicles, disc space, and lateral margin of the vertebral body are identified on the A-P view. The skin incision is made 1–2 cm laterally to the lateral margin of the vertebral body. This location will be more lateral than the UBE paraspinal approach. The instrumental portal is made 1 cm below the intervertebral foramen level, and the endoscopic portal is made 1 cm above this level. The distance between the two portals is about 2–2.5 cm, and the size of the incision is about 1 cm. The instrumental portal is made first, with the incision penetrating the fascial layer to maintain the continuous outflow of the irrigation saline during the surgery. Serial dilators are inserted sequentially, with the landing point of the first dilator initially touching the sacral ala or sacral notch, where the interspace of the superior articular process (SAP) of S1 and sacral ala is located (Fig. 11.7). The endoscopic portal is made in the same manner. The triangulation of the two portals is a cornerstone of this technique (Fig. 11.8). - Making initial working space
To obtain good initial operative visualization, meticulous dissection and detachment of muscular endings and soft tissue around the surface of the sacral ala or sacral notch are essential. The initial working space is the interspace filled with irrigation saline between the surface of the bony structure and soft tissue. This space is very narrow, but gradually widens by ablating or coagulating the soft tissue using an RF device. The initial working space is completed once the bony surface of the SAP lateral aspect, sacral ala, and lower border of the TP are clearly identified. The triangle zone of these three structures is the true working space. Additionally, the lateral aspect of the isthmus and sacral notch can also be easily identified (Fig. 11.9). - Removal of bony structures and soft tissue
After fully exposing these bony structures, drilling begins on the sacral ala, lateral aspect of SAP, and inferior border of the TP. Exposure of cancellous bone sometimes induces severe bony bleeding, which can be controlled by bone wax or an RF probe. Drilling laterally to the TP and ala reveals the pseudo-articulation, which should be removed as laterally as possible because the exiting nerve root runs under this pseudo-articulation (Fig. 11.10a). Further drilling and soft tissue removal using an RF device allow identification of the ligamentum flavum covering the exiting nerve root (Fig. 11.10b). - Identify the exiting nerve root and alar resection
After dissecting the lower part of the TP and along the fissure of the ligament flavum, the exiting nerve root is identified (Fig. 11.11a). The ligamentum flavum is removed easily and safely using a small Kerrison punch or angled curette (Fig. 11.11b), exposing the foraminal portion of the exiting nerve root. The annulus of the intervertebral disc located just below the nerve root is also identified (Fig. 11.12a). For complete decompression, the medial part of the alar and pseudo-articulation part must be further removed by drilling or using a Kerrison punch (Fig. 11.12b). - Finish the decompression and wound closure
In cases of severe bulging disc or disc herniation, discectomy is performed using pituitary forceps or Kerrison punch for full ventral decompression of the nerve root (Fig. 11.13a). Clarifying the ventral decompression of the nerve root is crucial for improving the prognosis post-surgery. Decompression is complete when the root is confirmed to pass freely through the alar and enter the abdominal cavity. The final image checks details, including the foraminal and extra-foraminal portions of the exiting nerve root (Fig. 11.13b). A drain catheter is inserted through the instrumental portal before skin closure (Fig. 11.14). After approximating the subcutaneous layer using absorbable suture material, the skin is closed with a skin stapler or non-absorbable suture.