Full-Endoscopic Lumbar Discectomy for Two Contiguous Level Adolescent Lumbar Disc Herniation

Background: Symptomatic lumbar disc herniation is rarely seen among adolescents. Adolescent lumbar disc herniation (ALDH) accounts for 0.5% to 6.8% of all those treated. Evidently, to our knowledge, no studies have emphasized the operative technique to treat two contiguous level adolescent lumbar disc herniation simultaneously. In this study, we aim to investigate the feasibility and advantages of one-stage full-endoscopic lumbar discectomy (cid:0) FELD (cid:0) for two contiguous level ALDH. This is the rst paper, to my knowledge, dealing with two contiguous level ALDH simultaneously with one-stage full-endoscopic lumbar discectomy. Methods: Between January 2014 and December 2019, patients received FELD surgery for lumbar disc herniation (LDH) in 2 main minimally invasive spine center of China were selected for screening of this study. Data of 5877 cases were retrospectively analyzed (2780 cases and 3097 cases, respectively). The inclusion criteria were patient under 21-year old, two contiguous level symptomatic lumbar disc herniation received one-stage 2 level PELD surgery. Visual analog scale (VAS) scores and modied Macnab criteria were used to assess the preoperative and postoperative clinical results. Results: 11 patients were enrolled in this study (0.19%,11/5877), 8 patients were male and 3 were female. 9 patients with LDH in the same side underwent single-incision 2 level FELD surgery via transforaminal approach. 2 patients with LDH in different side underwent FELD surgery via combined transforaminal and interlaminar approach. There were no immediate perioperative complications. The visual analog scale (VAS) decreased signicantly in both early and late follow-up evaluations and these score demonstrated signicant improvement in late follow-up (P <0.01). For the modied MacNab criteria, the nal outcome results were excellent in 9 patients (81.8%), good in 1 patients (0.9%), fair in1 patients (0.9%), and the overall success rate was 90.9%.


Background
Symptomatic lumbar disc herniation is rarely seen among adolescents. Adolescent lumbar disc herniation (ALDH) accounts for 0.5% to 6.8% of all those treated [1][2][3][4]. Evidently, two contiguous level adolescent lumbar disc herniation is less common. So far, the treatments available for ALDH and the effect of each treatment have not been fully reviewed [2].Patients who have failed in nonsurgical therapy, suffering from the progressive neurologic de cit or debilitating pain, surgical treatment is usually recommended. Nowadays, even though full-endoscopic lumbar discectomy (FELD) has rapidly evolved and gained popularity, but the e cacy of FELD is still controversial for symptomatic two contiguous level ALDH [5,6,10]. To our knowledge, currently, no studies have emphasized the operative technique to treat two contiguous level ALDH simultaneously. In this retrospective study, we aim to investigate the feasibility and advantages of one-stage full-endoscopic lumbar discectomy for two contiguous level ALDH.

Patients
This study was approved by the Ethic Committee of The Zhongda Hospital Southeast University(CODE: 2020ZDSYLL080-P01). The minimally invasive spine department of these 2 hospitals are main minimally invasive spine centers of China (more than 800 FELD surgeries per year) .
Between January 2014 and December 2019, a total of 5877 patients underwent FELD for symptomatic lumbar disc herniation, 2780 cases in Zhongda Hospital Southeast University and 3097 cases in Peking University Third Hospital. Data of these patients were retrospectively analyzed.The inclusion criteria of this study were: (1) patient under 21-year old; (2) radicular leg pain caused by multilevel lumbar disc herniation; (3) failure of conservative measures for a minimum of three months; (4) progressive neurologic de cit or debilitating pain.
The exclusion criteria were: (1)the presence of segmental instability; (2) cauda equina syndrome; (3) patients with other serious systemic diseases. (4) patients with incomplete data or patients who were lost to follow-up.

Surgical Procedure
All surgeries were performed by the experienced surgeon (660 per year). Transforaminal approach ("TESSYS" techniques) described by Hoogland et al. [7] and interlaminar approach(YESS"techniques) described by Ruetten et al. [8] were applied. All the surgeries were performed under local anaesthesia (0.5% lidocaine)and sedated with midazolam and fentany, which allow for monitoring of any changes of the patients' symptoms and make it possible for surgeons to get instant feedback from patients so as not to cause damage to any neural structures. The patient was placed in a prone position or lateral position on the radiolucent operating table. To determine an appropriate entry point and approach angle, preoperative images should be used to calculate and determine an appropriate puncture point and approach angle. (Fig. 1A). The point also depends on the location of the herniated disc, patient's body size and land foraminal dimension.

Single-incision 2-level transforaminal FELD:
For patient with herniated disc in the same side (all levels)( Fig.1 A,B), transforaminal FELD via single incision was applied. The single puncture point is determined by the intersection of two line, which the needle tip directed downwards making an angle of 10° -30° with the upper endplate of the distal vertebrate. Under lateral x-ray uoroscopy (Fig.1C), the line connecting the superior facet margin was marked as the safety line [7][8]. After routine disinfection, the single puncture point was generally 10-14 cm from the midline, and a long 18-gauge spinal needle was inserted from the entry point toward the midline under intermittent uoroscopic guidance. The superior facet joint was used as anatomic marker to avoid puncturing injuries and compressions to the existing nerve root. The needle was then replaced with a 1-mm-diameter guide wire. After a 10-mm skin incision was made close to the guide wire, and serial dilators and an obturator are introduced. The foramina were enlarged with a saw (Fig. 1C,D,E,F) . The surgeons usually operate the lower level at rst. The working cannula is the beveled type with an 8 mm outer diameter.
Since the intervertebral foramen was adequately enlarged with a saw, additional maneuvers like levering the working cannula to make it more horizontal, downward or upward tilting could be easily achieved. The intervertebral disc was excised with the aid of an endoscope. An endoscopic rongeur was used to remove the degenerated nucleus, which was then sent for pathological examination [7][8][9]. The decompression was concluded when the dura and spinal nerves were clearly visibly decompressed and the pulsation of the dural tube and the nerve root was con rmed, which was an important indicator of thorough decompression and surgical termination [9][10]. After complete removal of disc, the ventral dura demonstrated free pulsation with the Valsalva maneuver. Annuloplasty was typically performed at the end of the discectomy and minimal damage to the posterior structures. Hemostasis was performed with bipolar diathermy. The endoscope was removed after no active bleeding was con rmed [9].

Postoperative Management
After resting in bed for 1 days postoperatively, the patients could have off-bed activity appropriate with a protective belt and begin lumbodorsal muscle exercise and straight leg-raising exercise. One week later, the patients resumed light physical labor. In the rehabilitation period, to achieve favorable healing of the ruptured annular brosis and decrease recurrence of disc herniation, wearing the lumbar back brace approximately 2-4 week was recommended.

Clinical assessment
Clinical chart review and telephone survey was performed. The outcomes of symptoms were analyzed using the VAS scores for low back and leg pain pre-operatively and immediately, at three and annually thereafter by an independent assessor. It is a continuous scale composed anchored by a score of zero, indicated no pain, and a score of 10, represented the worst pain. Modi ed Macnab criteria for the patient satisfaction [11].Excellent indicates no pain and no restriction of movement, allowing the patient to work normally; good indicates occasional pain, allowing the patient to work normally; fair indicates slight progress; poor indicates no progression.

Statistical analysis
The pre-operative and postoperative clinical results were statistically analysed using the Wilcoxon signedrank test to compare scores.

Demographic Data
In this retrospective study, a total of 11 patients (female/male: 3/9) were consecutively enrolled with a follow-up period of 17.3 months in average. 0.19% of all FELD surgeries in these 2 minimally invasive spine center. 4 cases affected the L3-L4 /L4-L5 level, and 7 cases affected the L4-L5 /L5-S1 level. The

Discussion
Disease occurring under 21-years of age is termed 'adolescent' [12][13][14]. But at what age there is a relevant distinction from adult disease is unclear. Great care should be taken when operating on the immature spine due to that it is unknown whether operating on the immature spine may increase their risk for having spinal surgery in the future [13]. Additionally, delaying surgery for conservative treatment is warranted, but for how long remains unclear.
Appropriate conservative treatment including (bed rest, physical therapy and (NSAIDs) is the rst choice for adolescents, but the young patients do not respond as well to nonsurgical treatment as adults due to adolescent disk material often remains well hydrated [13][14][15]. The surgical aim of treatment for ALDH is achieving of appreciable pain relief and function improvement. Mixter and Barr [16], published the rst report of a herniated nucleus pulposus in a child in 1934, with another report of surgical treatment for a 12-year-old boy by Wahren in 1945 [17]. Traditionally, open discectomy (OD) and microendoscopy discectomy (MED) was employed as the standard operation for ALDH [18,19].
In recent years, minimally invasive techniques are an attractive alternative to open discectomy (OD) and microendoscopy discectomy (MED) with a view to improving management of ALDH patients [18,19].
Endoscopic techniques have been widely used for ALDH since the rst introduction by Ruetten et al [8]. It has unique advantages of minimizing trauma to the normal spinal structures, reducing intraoperative bleeding and allowing earlier return to work. Most studies [10,12,13] have since been published on the surgical management of single level (especially L4-L5 or L5-S1) disk herniation in children and adolescents. Due to the sample size of 2 contiguous level ALDH is relatively small and rarity of its incidence, even though FELD has rapidly evolved and gained popularity, but, the e cacy of FELD is still debatable for contiguous ALDH. To our knowledge, currently, those studies had not mentioned one-stage operation of full-endoscopic lumbar discectomy for 2 contiguous level ALDH simultaneously [9][10][11][12][13][14].
Anatomically, inclination of L5-S1 disc spaces steeper than the L4-L5, which making single entry puncture point is enough to perform PELD at both the L4-L5 and L5-S1 levels. According to described technique [5,10], in cases of L4/L5-L5/S1 ALDH, under uoroscopic guidance the meeting point of two lines crossing the L5 and S1 facet joint, indicating the point through which the surgeon can perform PELD for two level ALDH. In case of L3/L4-L4/L5 herniation, a small single skin puncture point is also possible, which rely on the technique of rod adjustment of a working cannula and targeted fragmentectomy. The favorable indications for one-stage operation of transforaminal full-endoscopic lumbar discectomy are same-side two level lumbar disc herniations causing unilateral radicular leg pain [10]. However, the transforaminal approach at L5-S1 has limitations in cases of high iliac crests, small intervertebral foramen, large migrated disc herniations and different side lumbar disc herniations [12]. In this study, 2 patients underwent one level transforaminal endoscopic lumbar discectomy combine one level endoscopic interlaminar discectomy. Because of this 2 pantients indicated different side lumbar disc herniations causing bilateral radicular leg pain.
The distinguishing feature of adult LDH was a result of age-related degenerative process of the spine. However, ALDH must be explained another cause such as micro-trauma, because degeneration is infrequent in adolescents [22][23][24]. But in actual fact the pathogenesis of ALDH is unclear, trauma or sports-related incidents, genetics and dysfunctional bio-mechanical conditions ( being overweight, or being tall, congenital lumbosacral malformations ) are likely contributory [21][22][23][24][25]. This study indicated that students accounted for 77.7%, we speculate that hours spent sitting is a major risk factor due to increased axial load. In our study, attening of the sagittal lumbar curvature happened in 7 cases (63.6%). Other studies demonstrated that attened spines are often associated with degeneration of multiple discs and back muscle weakness, which further signi cantly decreases spinal exibility and stability [25,26,27] .
Several points should be kept in mind. (1) placement and rod adjustment of working cannula precisely, (2) toward the target compressing element of the disc directly, (3) require proper training and suitable patient selection.
Despite the sample size is relatively small because of rarity of its incidence with retrospective design, the absence of a control group and the follow-up period is too short to comment on the subsequent degeneration of the disc, our study suggests that one-stage operation of full-endoscopic lumbar discectomy for 2 contiguous level ALDH is an effective and less invasive method. To overcome the limitations, further studies are wanted to determine long-term therapeutic effect of one-stage operation of full-endoscopic lumbar discectomy for 2 contiguous level ALDH.

Conclusion
This study's data suggest that one-stage operation of full-endoscopic lumbar discectomy for 2 contiguous level ALDH is an effective and less invasive method that avoids open surgery and provides another stable and acceptable treatment option in proper patient selection.
Abbreviations ALDH Adolescent lumbar disc herniation We obtained ethics approval from the Research Ethics Committee of Zhongda Hospital Southeast University(CODE: 2020ZDSYLL080-P01). All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee. For this retrospective study, formal consent is not required.

Consent for publication
Not applicable.

Availability of data and materials
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no competing interests.
Authors' contributions LM: Drafting the manuscript and surgical treatment. BZh:Drafting the manuscript and surgical treatment XTW: Surgical treatment and conception, design and manuscript revision. FW: Data analysis and drafting the manuscript. CZ: Acquisition of the data. JZ: Analysis and interpretation of the data. All authors agree to the nal submitted manuscript and declare that they have no con ict of nancial interest.