PTED technic has been an effective and safe procedure for LDH[17–20]. Hoogland et al firstly invented the TESSYS technique, in which a graded trephine was used to enlarge the foramen gradually and the working channel slope is placed close to the intervertebral disc. However, the extruded and sequestered disc fragments are accessible only when the operating instruments are placed in the optimal trajectory. Accuracy was highly demanded,especially for the puncture and foraminoplasty procedure. At the L5-S1 level, the unique anatomy includes a high iliac crest, sacral ala, large L5 transverse process, large facet joint, narrowed disc space, and narrow foramen hindering safe and effective access through a narrow channel. The puncture[21], foraminoplasty and channel indwelling processes are complicated. An optimal trajectory may be hard to achieve or inaccessible, which leads to a steeper learning curve[22] and challenges, even for skilled surgeons. In addition, the gradual trephine is isocentric, which increase the risk of damage to nerve roots. Most POD cases due to dorsal root ganglia stimulation or injury have been reported to occur in L5-S1 during the PTED procedure[23, 24]. To address the above problem, the ZESSYS, a targeted and quantificational foraminoplasty device with a double-cannula is conducive to overcoming the anatomic limitations at the L5-S1 level.
Firstly, it can reduce the difficulties of acupuncture. In our study, the average puncture time(5.29 ± 2.05 minutes) in the ZESSYS group were significantly shorter than those in the TESSYS group (average puncture time 8.07 ± 3.13 minutes, p < 0.01). In the conventional TESSYS technique, an18-gauge needle is inserted toward the middle line of the vertebral canal under AP imaging and toward the vertebral posterior superior margin under lateral imaging, and subsequently, foraminoplasty is performed to achieve a sufficient level of surgical access for PTED. If needed the targeted point can be adjusted for special extruded and sequestered disc fragments. When the high iliac crest, large L5 transverse process, and large facet joint obstruct to the trajectory at the L5-S1 level,the ideal or targeted puncture point is time-consuming, difficult or even inaccessible to reach, and the foraminoplasty time and fluoroscopy time increase correspondingly. ZESSYS is a dual-cannula adjustment instrument with a thin cannula containing a Kirschner wire for orientation and a larger cannula for bony abrasion by a trephine(Fig. 1). Primary puncture with an 18-gauge needle was only demanded to across the safe triangle area stepwise, after the guidewire was introduction and graded dilation was performed, the traditional guidewire was replaced with a 1-mm Kirschner wire and slightly hammered to fix on the posterior aspect of the distal vertebra, which could guide the following introduction of the dual-cannula device for foraminoplasty. The trajectory of the Kirschner wire did not need to strive for the accurate requirement of TESSYS technique; it was necessary to insert the wire between the exiting nerve root and the SAP, and it could be fixed at any position near the superior-lateral part of the posterior aspect of the distal vertebra. The double-cannula system take advantages to rotation and can be easily adjusted to find a proper and targeted entry point on the SAP, which can compensate for the Kirschner wire primary puncture point(Fig. 2). In addition, depending on the last trajectory of the Kirschner wire, size 4 of the graded dual-cannula size may be selected for selective resection of the SAP for quantificational foraminoplasty(Fig. 1, Fig. 2). However, as a rule, an extruding or sequestrated disc fragment is within the scope of the working channel’s coverage. In addition, if predetermined effective access to enter or across the safe triangle area is hard to achieve or inaccessible by using an 18-gauge needle in the case of a large L5 transverse process, large facet joint, narrowed disc space, or narrow foramen impeding the predefined trajectory, after replacement, the Kirschner wire can take place of the needle for the puncture process as it is more rigid and easier to adjust. In particular the use of a Kirschner wire with a 1 mm diameter for trajectory adjustment and fixation in the safe triangle area increases the risk of nerve root damage, so when the Kirschner wire advances into the foramen, it should cling to the ventral aspect of the SAP, and the patient’s responses should be taken into consideration to avoid possible nerve root and adjacent soft tissue injury. If possible, the tip of the Kirschner wire should be fixed between the inner side of the SAP and the middle line in the anteroposterior view, thereby allowing a small amount abrasion with the upper articular process.
Secondly, the ZESSYS device can improve the efficiency and safety of foraminoplasty. In this study, the average foraminoplasty time(12.82 ± 2.52 minutes) in the ZESSYS group were significantly shorter than those in the TESSYS group (average foraminoplasty time, 17.18 ± 2.92 minutes, p < 0.01). Among the anatomical limitations at the L5-S1 level, the iliac crest is considered a major obstacle[25, 26]. When the iliac crest is located above the middle of the L5 pedicle in the lateral radiograph, foraminoplasty may be required[27]. In addition, if the working spaces are limited by the other anatomical limitations, foraminoplasty is also necessary. In the conventional TESSYS technique the foramen is widened gradually by an isocentric trephine. During the process of foraminoplasty, the trephine blade makes close contact with foramen soft tissue and nerve roots, leading to a risk of damage, espically for the L5-S1 level with a narrowed disc space and intervertebral foramen than the other levels. During the PTED process with ZESSYS, a 1 mm Kirschner wire is passed between the SAP and exiting nerve root and fixed on the the posterior aspect of the distal vertebra, which acts as a steady pivot for the double-cannula device. When the predefined cannula is inserted to dock on the SAP at posterior orientation, it can be easily rotated to find the proper trajectory and achieve quantificationally decompression. In addition, the beveled design cannula is placed next to the ventral side of the SAP, excluding the exiting nerve root from the working zone of the trephine and protecting the exiting nerve root from damage. If needed, the foramen can be enlarged by a second cannula rotation. The double-cannulas greatly reduce the difficulty of foraminoplasty and enable foraminoplasty to be performed more precisely.
According to our study, the ZESSYS device is more efficient than the TESSYS device in the puncture and foraminoplasty procedures. The difference in the puncture time and foraminoplasty time between the two groups were significant. Not only that, the average fluoroscopy time (26.29 ± 5.96 seconds) and total surgery time(63.14 ± 7.76 minutes) in the ZESSYS group were significantly shorter than those in the TESSYS group (average fluoroscopy time, 34.73 ± 6.86 seconds; p < 0.01; total surgery time 74.21 ± 12.16 minutes, p < 0.01 ). The fluoroscopy time decreased with the application of ZESSYS, which was beneficial for both the patients and surgeons. The preliminary postoperative outcomes seemed to be equal between the ZESSYS group and TESSYS group. There were no significant differences in the VAS score for low back pain, VAS score for leg pain, ODI score or MacNab criteria between the two groups at the same time point. No cases of recurrent herniation were observed at the 12-month follow-up. However 1 patient in the TESSYS group experienced slight dysesthesia after surgery. Although his symptoms disappeared within 2 weeks after temporary conservative treatment. It is an alert of exiting nerve damage which is a common complication of PTED[18, 23, 28]. There were no cases of severe complications in the ZESSYS group. One of the reasons for this result might be that the new instrument not only effectively widened the foramen but also effectively protected the nerve root.
Nevertheless, our study has some limitations. Firstly, the sample sizes of the two groups were small, and the follow-up time was short. The clinical outcome was preliminary, and a larger study needs to be conducted in the future to verify the the reliability of the ZESSYS system. In addition, at the L5-S1 level, the unique anatomical limitations were triaxial and complicated, and there were no specific protocols for the evaluation of the anatomical limitations. Therefor, in this study, we analyzed two major anatomical limitations between the two groups, which may not be enough and may affect the statistical correctness.