With the development of surgical instruments and surgical techniques, the concept of PELD has shifted from indirect intervertebral decompression to epidural targeted decompression, and common types of disc herniation can be treated with PELD[3–7]. However, it is still a challenge for the very high-grade inferiorly migrated disc herniation. In the case of very high-grade inferiorly migrated disc herniation, endoscopic discectomy is less successful because endoscopic access to the lesion is often interrupted by anatomical structures, such as pedicle and narrowing of the foraminal space [7]. Lee et al[12]. analyzed 55 cases of failed endoscopic discectomy. The high-grade migration group showed a failure rate of 15.7% due to the inadequate scope of the operation, poor visual field, insufficient decompression, and residual disc. Therefore, they suggested that open surgery should be performed for high-grade migration disc herniation[12]. However, open discectomy will inevitably destroy paravertebral muscles, vertebral lamina, and articular processes, affecting spinal instability[6]. To overcome these limitations, some methods have been developed, such as the extreme lateral approach, epiduroscopic approach, superior vertebral notch approach, and suprapedicular approach[6, 13–16]. No matter what surgical approach, the most fundamental breakthrough is that the working cannula should be as close to the target as possible[6]. The superior notch of inferior vertebral pedicle approach is a method of removing a migrated disc through the narrow space of the intervertebral foramen in the transitional region between the superior notch of the pedicle and the posterior margin of the vertebral body. Through the foraminoplasty and the removal of partial cancellous bone from the posterior superior margin of the lower vertebral body, the working cannula can be inserted into the target. The superior notch of inferior vertebral pedicle approach has several advantages. This approach requires that the needle should have a certain cephalad and lateral angle, which is greater than that in the TESSYS (transforaminal endoscopic spine system). The channel is longer than that of the TESSYS and can reach the inferior border of the pedicle and even the lower endplate of the inferior lumbar vertebrae. Expanded the surgical space and decompression range of the spinal canal. The dural sac can be exposed inwards, and the external orifice of the intervertebral foramina can be reached outwards. The exiting nerve root can be exposed upwards and the compression of the nerve root caused by the degenerated annulus fibrosus or osteophytes at the posterior border of the lumbar vertebral can be relieved. The inferior border of the vertebral pedicle and even the lower endplate of the inferior lumbar vertebral body can be reached downwards. The compression of the dorsal and ventral nerve roots can be completely alleviated.
For very high-grade inferiorly migrated disc herniation, targeted puncture, foraminoplasty, application of endoscopic grinding drill, and adjustment of working channel scope are particularly important to ensure the success of the operation. An optimal puncture trajectory should always aim at or approach the target as much as possible, which is most important for herniated fragments[5, 6, 17]. Because as close as possible to the target, it is conducive to the foraminoplasty, and the obstruction of the articular process to the working cannula can be minimized in the subsequent operation. For cases of very high-grade inferiorly migrated disc herniation, the entry point should have a certain cephalad and lateral angle. The puncture target was located in the midline of the anterior and posterior fluoroscopy and in the superior notch of the lower vertebral pedicle the lateral fluoroscopy (Fig. 2). For the L4/5 and L5/S1 levels, due to the obstruction of the iliac crest, articular process, and transverse process, it is sometimes not possible to accurately puncture the target, and curved guide rods can be used for fine adjustment. Foraminoplasty is helpful in order to be able to enter the epidural space and obtain high-grade migration fragments[6]. However, this procedure may lead to nerve injury and the tip of the articular process damage, increase the risk of postoperative segmental instability and lead to the most common complication of postoperative dysesthesia[5, 6, 18–20]. Therefore, the procedure should pay close attention to the patient's pain response during operation and adjust according to the situation of fluoroscopy. In this study, the resection area of foraminoplasty is the ventral side of the superior articular process. This area is the safest anatomical point, farthest from the nerve root. This procedure may reduce the risk of the exiting nerve root injury during operation to some extent on the basis of the anatomic relationship between exiting nerve root and foramen. There were two cases (6.2%) suffered from postoperative transient dysesthesia in this group of patients. The reasons may be irritation associated with the surgical approach, excessive intraoperative manipulation, and early unfamiliarity with the posterior lumbar anatomy. VAS leg scores improved from 8.42 ± 1.21 to 2.12 ± 0.86, and ODI improved from 68.45 ± 9.32 to 24.86 ± 8.32. The overall excellent and good rate was 93.8% on the basis of the modified MacNab criteria. In recent years, other endoscopic techniques have reported an overall success rate of high or very very high-grade migrated disc herniation ranged from 84.6–100%[3–5, 13, 21] (Table 5). Our results are basically consistent with those reported by other endoscopic techniques. In our opinion, this technique is difficult to directly compare with the previously reported methods, because the diagnosis of the study population is different and the surgical techniques are also different. However, compared with other endoscopic techniques, it may be helpful to prove the efficacy of the superior notch of inferior vertebral pedicle approach.
Table 5
Comparison of clinical and surgical results with other endoscopic techniques
Author | Number of patients | Diagnosis | Mean operative duration (min) | Mean hosiptal time (day) | Mean follow-up period (month) | Surgical technique | Success rate (%) | Complication |
Lee CW et al. [5] | 64 | Highy migrated, High canal compromised, combined with foraminal stenosis | 45.6 | 1.54 | 12.2 | Foraminoplastic superior vertebral notch approach | 95.3 | 2 dysesthesia 1 reoperation |
Wu X et al. [21] | 22 | highly migrated lumbar disc herniation | 88.86 | 1.68 | 18.1 | Two-level PELD | 90.9 | 1 dysesthesia 1 reoperation |
Ahn Y et al. [4] | 13 | Very high-grade lumbar migrated disc herniation | | | 12 | PELD with foramionoplasty | 84.6 | 1 dysesthesia |
Chae KH et al. [13] | 53 | Highly inferior Migrated disc herniation | 90 | 1.33 | 9.8 | Suprapedicular approach | 88.8 | 7 dysesthesia |
Kim HS et al. [3] | 18 | high grade inferiorly migrated lumbar disc herniation | | | 8.4 | PELD with suprapedicular circumferential opening technique | 100 | No |
Present study | 32 | Very high-grade inferior migrated disc herniation | 68.2 | 3.6 | 12 | Superior notch of inferior vertebral pedicle approach | 93.8 | 2 dysesthesia |
PELD: percutaneous endoscopic lumbar discectomy |
When the inferiorly migrated disc material is beyond the visual scope of the endoscope and cannot be completely removed, under the premise of protecting the nerve root and dural sac, part of the superior margin of the lower vertebral body or part of the articular process bone was removed with a grinding drill to expand the surgical space. During the operation, the working cannula can be adjusted to the dorsal, ventral and even contralateral sides of the nerve root to perform all-around decompression according to specific conditions. Although our surgical data showed a favorable clinical outcome, the safe range of removal of the posterior superior margin of the lower vertebral body is not completely clear. Our experience is to remove bone as little as possible without affecting the surgical procedure. It is needed to observe the potential risk of vertebral fracture and the stability of the spine over a long time. Don't rush to remove the migrated disc material when it was found during surgery. The surrounding fibrous rings, posterior longitudinal ligaments and scar tissue should be released first. Shake slowly with the strength of the wrist, which will facilitate the complete removal of the migrated disc material. It is strictly prohibited to "Violent tugging" to avoid remnant disc fragments, or even nerve root or dura mater injury. In the case of ensuring sufficient decompression, the surgical operation of the tissues such as the posterior longitudinal ligament, ligamentum flavum and other tissues should be minimized to prevent tissue adhesion after surgery. The removal of the migrated disc material and the removal of the superior margin of the lower vertebral body or the articular process bone are often accompanied by bleeding, resulting in blurred operative filed. Do not operate at this time, so as not to avoid side injuries. The bleeding site can be controlled naturally by means of the working cannula compression hemostasis. Appropriate pre-hemostatic treatment of the surrounding tissue was performed with radiofrequency before removal of the migrated disc material, which is helpful to reduce intraoperative bleeding. In addition, hemostasis can be achieved through high-pressure fluid irrigation, absorbable gelfoam and other hemostatic materials.
There are some limitations to our study. First, it was a retrospective analysis of cases in a single institution. Second, this study has a small sample size and a lack of the control group and short duration of follow-up. Long-term large sample study and follow-up observation are needed to evaluate the clinical outcomes.