The standard arthroscopic facilities and conventional spine instruments such as Kerrison rongeurs, pituitary forceps, curettes, and high-speed diamond burrs are used.
Room setup and patient positioning
The fluoroscopy unit and the video equipment for the endoscope. The procedure is performed under general or epidural anesthesia. The patient is placed in the prone position with the abdomen free over the radiolucent chest frame in a flexed position to open the interlaminar space and foramen.
Endoscopic portals placement
Under image intensification, fluoroscopic confirmation of the level is made with a spinal needle inserted at the target area. Skin entry points are determined according to the lesion site and the patient’s anatomical variation. Two standard entry points are made at 1 cm above and below the disc space for a posterior approach (Fig. 5) and at the foramen level for the posterolateral approach (Fig. 6). The fascia is opened approximately 7 mm with a 15-blade scalpel along the skin crease followed by blunt muscle-splitting technique [2, 3] with a serial dilator touching the lamino-facet joint junction. Position is confirmed with biplanar fluoroscopy.
Insertion of the endoscope and preparation of the surgical field
The posterior approach is accomplished via two portals through the intermuscular septum separating erector spinae and multifidus muscles using serial dilators. The multifidus muscle is saved by detaching the muscle from the lamina without injury with a blunt dissector to prepare a working space. This technique offers benefits over other techniques, such as the microendoscopic procedure, by creating a potential fatty space between the multifidus muscle in which to avoid crushing injury from over-retraction. We achieve a clear visual field with saline irrigation in this working space, which is used as the cavity-like joint space in arthroscopic surgery (Fig. 3).
Laminotomy/medial facetectomy/ligamentum flavum removal
Thereafter, via a working cannula, conventional surgical instruments, such as the burr, punch, curette, and pituitary forceps, can be used freely in various access angles.
Depending on the pathology, ipsilateral decompression is performed first by performing hemilaminotomy with a drill and a Kerrison rongeur until the superior edge of the deep part of the ligamentum flavum in exposed. Hypertrophied facet joints and the lamina are undercut by drilling; then a blunt hook dissector is used to identify the plane between the ligament and the dura, ensuring that it is free from adhesions, and a curette and a punch can be used to peel off the ligaments and relieve the neural structures. If bilateral decompression is required, the midline of the spinal canal must first be confirmed by resecting the base of the spinous process with a high-speed drill. The scope can then be adjusted medially. Usually the base of the spinous process obstructs the placement of the scope, therefore it may need to be partially resected to secure sufficient working space. Once exposed, the ligamentum flavum can be detached from the contralateral lamina and then undercut with a burr. The entry to the contralateral side is performed dorsal to the dura with the ligamentum flavum intact for protection. Bony decompression is performed again using cranial and caudal laminotomy. Medal partial facetectomy of the contralateral superior articular process is performed to preserve the facet joint integrity. After bony decompression, thickened ligamentum flavum is resected with a curette to fully relieve the neural structures [5, 7]. The use of Kerrison rongeurs, a high-speed drill, and an ultrasonic bone cutter enables the lateral recess to be enlarged while keeping the facet joint intact. The endpoint of decompression is the outer edges of the bilateral nerve roots . Continuous saline irrigation at 25 to 30 mmHg maintains a clear surgical view and preserves the epidural fat and vessels from damage, which may happen during the microendoscopic decompression surgery. This technique also avoids increased epidural hydrostatic pressure and subsequent increased intracranial pressure. Laminotomy and flavectomy is performed in a similar fashion as microscopic surgery, but bleeding is more effectively controlled by the radiofrequency bipolar system under continuous irrigation.
In case of foraminal stenosis, a working space around the foramen is achieved by meticulous dissection with a blunt dissector under clear vision and variable angle view. First, landing on the superior articular process is one of the important keys to the operation. The procedure begins at the safe extraforaminal area. Initial decompression of the superior articular process is performed sufficiently so that the exiting nerve is decompressed more safely without much manipulation. Out-in decompression around the nerve under wide view is of paramount importance .