Compared with other surgical disciplines including open surgery and sports medicine in orthopedics, endoscopic minimally invasive surgery has been considered to be a sensible method that satisfies the demands of the quicker recovery for LDH in recent years [7]. Minimally invasive spinal surgery is gaining popularity because its several advantages, including restoring functions while preserving normal anatomy, minimizing hospitalization and complications associated with extensive open procedures, and helping elderly patients return to active premorbid status as early as possible [6]. Endoscopic lumbar intervertebral fusion has been reported. Since the incidence of complications is as high as 36%, it is not recommended by Jacquot et al [5]. However, ZWLIF technique can finish lumbar intervertebral fusion and percutaneous screw fixation safely without technical limitations. To the best of our knowledge, no study on ZELIF has been reported yet. Thus, we intended to share a relevant technical note.
Numerous prevenient studies have discussed the anatomical structure of intervertebral foramina in the lumbar spine, so as to measure the maximum working channel space suitable for undergoing endoscopic discectomy manipulations [11-14]. In 1995, Mirkovic et al. [13] reported the size of the safe edge for a channel in the intervertebral foramen. In 2005, Min et al. [12] demonstrated that the average distance between the superior articulating process and the exiting nerve root was 11.6 mm. In 2016, from a cadaveric study, Hardenbrook M et al. [15] reported a relatively large area in the lumbar intervertebral foramen, called Kambin’s triangle. Therefore, we believe that the ZELIF channel is safe to be installed through Kambin’s triangle, and this idea has been agreed by Ozer et al. [10]. Although it is theoretically safe, INM is carried out to prevent nerve injury.
Indications of this technique include (1) LDH with segmental instability, (2) lumbar spinal stenosis with segmental instability and (3) lumbar spondylolisthesis of lower than Meyerding grade II. Contraindications mainly include (1) L5-S1 lumbar disc herniation due to the high ilium which affects the installation of the channel, (2) variation of the nerve root, (3) lumbar spondylolisthesis of higher than Meyerding grade III, and (4) severe central canal stenosis.
Advantages of ZELIF include shorter operation time, less blood loss, shorter hospital stays, a very low risk for pulmonary embolism, less soft tissue destruction, less pain, quicker restoring the function of standing and walking, and no need for drain postoperatively [5]. In addition, the decompression of dura and the nerve root was performed under endoscope and INM, avoiding nerve injury and improving the safety of operation.
Literature reports suggest that smaller fusion cages must be used when endoscope-guided intrabody cages are placed, because traditional fusion cages are too large to pass through working channels [5, 16]. However, the undersized cage may directly cause cage migration into the intervertebral foramen or spinal canal, thus leading to neurological compromise, failure of fixation, or even revision operation [17, 18]. The ZELIF technology uses a specially designed C-shaped open channel, which can realize the installation of conventional cages under fluoroscopy without size reduction. In this study, cage migration was not observed during 1 months of the follow-up, and we attribute this positive result to the ZELIF technique.
INM has been commonly utilized to avoid nerve damage in spinal surgery [9, 19], and considered by many scholars as a reliable method to avoid nerve injury [9, 19, 20]. Even if there are no neuromonitoring events during the operation, we believe that it is necessary to monitor the functional state of the nerve root, especially in the process of channel installation. We suggest that once abnormal nerve monitoring is found, the installation direction of the channel should be adjusted in time.
The following points should be paid attention to during the operation: (1) After the establishment of the channel, it is suggested that the assistant should fix the channel by hand to avoid it sliding out due to improper operation; (2) If the channel is taken out accidentally, please re-enter the guide wire and re-install the channel. Blind direct installation of the channel is forbidden; (3) Careful examination of the patients should be performed preoperatively, and nerve root variation is not suitable for ZELIF; (4) INM is recommended during all surgical steps.