With the rise and development of precision medicine, minimally invasive surgeries aimed to cure disc diseases are more and more common, and the development of percutaneous endoscopy technology makes it possible to treat spinal diseases accurately. [14, 21–24]However, the learning curve of PTED technique is steep, which is difficult for many beginners to administer. The poor curative effects and complications were common mostly because of the ambiguous anatomy under the endoscopy, so it is urgent to explore a still and distinct symbol to instruct the surgeons to recognize other tissue.
Transforaminal endoscopic spine system (TESSYS) technique successfully dissolves the problems of introducing the intervertebral foramen and provides surgeons a relatively safe tunnel that leads to the spinal canal.[26, 27] However, despite the fact that scholars have their methods to probe to the spinal canal and recognize tissues, there is no common and clear standard in how to do them. Sometimes beginners find it hard to identify the surrounding tissues after setting the endoscope when they puncture successfully according to the TESSYS technique(The anteroposterior position was located in the midline of the spinous process, and the lateral position was located in the posterior upper margin of the lower vertebral body). Actually, the endoscope lens has already been stuck into the herniation disc, which is full of soft tissues, and for beginners, it is difficult to distinguish the orientation and location of spinal dura mater and nerve root, like a ship on sail without lighthouses’ guide.
selection of insertion point
The insertion point is selected horizontally on the back facing the side corner, generally located on the upper side of the responsible intervertebral space, and it can be parallel to or below the intervertebral space depending on the level of disc herniation as well. This insertion point is typically inwards than that of TESS technique with the advantages of the large puncture angle on the coronal plane and low probability of damaging the exiting nerve root.
When it comes to high-level disc herniations, especially upper than L2/3, choosing this insertion point can avoid the injury of abdominal and retroperitoneal viscera. It can also avoid the barrier of the iliac crest and the transverse process of L5 to the maximum extent in the cases who have an L5/S1 disc herniation(Figs. 5), particularly with iliac crest and L5 transverse process. Because the soft tissue is loose in the horizontal back facing the side corner, the tunnel can be easily adjusted by lowering or raising the guide stick, so that the endoscope can reach the aim position smoothly. 
Intervertebral foramen formation
In the SapON technique under the fluoroscopy, if the needle tip was inclined to the proximal end, the guide stick should be moved to the distal end, otherwise to the proximal end. If the needle tip was laterally inclined, the guide stick should be properly lowered, and if it is too medial, the guide stick should be appropriately raised. After adjusting the angle of the guide rod, we perform an articular process osteotomy with a 7.5 mm trephine right the first time through an 8.8 working cannula. The trephine was attached to the dorsal side of the superior articular process, and we discover the following advantages:(1)The oblique plane of the 8.8 working cannula is toward the articular process, successfully keeping the exiting nerve root out the cannula to prevent the nerve root from hurt. (2)The angle of the trephine can be adjusted according to the location in the frontal x-ray fluoroscopy. If the trephine tip is outwards, it can be held against the superior articular process and used as a fulcrum to depress the trephine on the coronal plane, so that the trephine tip will enter the spinal canal after osteotomy. Conversely, if the trephine tip is inwards, it can be raised on the coronal surface so that the trephine tip will not enter the spinal canal too deep to injures nerve roots in the spinal canal after the obvious sense of resistance. When the resistance disappears, the trephine is stopped, at this time, the position of the trephine tip is exactly right at the inner opening of the intervertebral foramen. Then the protection will be taken effect after the trephine is stoped to avoid the injury of nerve roots in the spinal canal.
Operations under the endoscope
We use the superior articular process Osteotomy surface as the navigation symbol to distinguish the tissues after the osteotomy. Structures were distinguished through the navigation of the osteotomy surface of the superior articular process. The osteotomy surface is the posterior wall of the intervertebral foramen while the fiber annulus is in front. The proximal end is the exit nerve root, and the distal end is adjacent to the pedicle. After going into the cannula, a herniated disc annulus (inclusive herniation) or nucleus pulposus (ruptured herniation) can be seen in orientation of 6 o'clock, and the ligament flava can be seen in orientation of 12 o’clock, deeper in the ligament Flava locates the looming adipose tissue (pushed backward by the herniated disc) in which the nerve roots locates.
According to the order of anatomy, we discover that when probing from outside to inside, the navigation symbol helps us identify the crucial structures and offers surgeons a clear sense of orientation, which leads to exact operations. So the learning curve will be reduced for beginners to manage it.
But in TESS, the endoscope is placed into the center of the spinal canal by surgeons. The surrounding view under the endoscope is filled with different kinds of soft tissues so that it is still hard for surgeons to identify the anatomic structures, although the blood clots are removed. Due to the patient is in the lateral position; the direction under the endoscope is opposite to the direction of realistic operations, it is hard for new learners to distinguish the orientation suddenly. So it would spend plenty of time probing to aim area, let alone removing the debris of nucleus pulposus.
Exposure of the X-ray fluoroscopy
The vital operation of percutaneous endoscopic lumbar discectomy lies in how to precisely set the endoscope, which relies on the help of X-ray fluoroscopy. In the classic TESS technique, the patients are frequently exposed to the radiation to ascertain the structures from confirming the insertion point to shaping the intervertebral foramen.
In this study, the SpON technique we used remarkably assists in reducing fluoroscopy times. In theory, confirming the insertion point needs fluoroscopy once, puncturing in place requires anteroposterior and lateral fluoroscopy twice, and shaping the intervertebral foramen requires anteroposterior and lateral fluoroscopy three times with a total five times of fluoroscopy to the minimum. But because of the initially unfamiliar utilization of the surgery technique, the average time of fluoroscopy was 13.27 ± 4.38 times. Although the realistic times of fluoroscopy are more than those, in theory, they are apparently fewer than
those in TESS technique(23.68 ± 6.70 times), which means the degree of patients' and surgeons’ exposure to radiation is significantly reduced.