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Full-Endoscopic Interlaminar Lumbar Discectomy: Retrospective Review of Clinical Results and Complications in 545 International Patients
Original Article
Full-Endoscopic Interlaminar Lumbar Discectomy: Retrospective Review of Clinical Results and Complications in 545 International Patients Kanthika Wasinpongwanich1,2, Krit Pongpirul3-5, Khin Myat Myat Lwin1, Withawin Kesornsak1, Verapan Kuansongtham1, Sebastian Ruetten6
BACKGROUND: Minimally invasive techniques have been developed to provide access to the disc with better visualization while causing less muscle trauma and its consequences. This study was aimed at evaluating the clinical outcomes and complications of the fully endoscopic lumbar discectomy interlaminar approach in a large number of patients.
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METHODS: Patients diagnosed with lumbar herniated nucleus pulposus who underwent fully endoscopic interlaminar lumbar discectomy between 2011 and 2016 were reviewed. Perioperative data, preoperative and postoperative Oswestry Disability Index (ODI) scores, visual analog scale (VAS) back pain scores, VAS leg pain scores, and complications were evaluated and recorded at 1 week and 3 and 6 months postoperatively and each year thereafter.
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RESULTS: The study cohort comprised 545 patients (average age, 46.43 years; 34.31% female). The affected levels were L2-3 in 1.47%, L3-4 in 6.96%, L4-5 in 49.45%, and L5-S1 in 44.69%. Mean preoperative ODI, VAS back pain score, and VAS leg pain score were 43.00%, 5.00, and 5.69, respectively. Postoperative ODI at 1 month was reduced to 15.59% and remained within a range of 14.83%18.32% throughout follow-up. Postoperative VAS back and leg pain score results at 1 week were decreased to 1.66 and 1.79, respectively, and remained at 1.89e3.14
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Key words Endoscopic discectomy - Full endoscopic lumbar discectomy - Herniated nucleus pulposus - Interlaminar discectomy - Lumbar disc herniation - Lumbar discectomy - Percutaneous endoscopic discectomy -
Abbreviations and Acronyms FEILD: Fully endoscopic interlaminar lumbar discectomy ODI: Oswestry Disability Index PPL: Posterior longitudinal ligament VAS: Visual analog scale
and 1.59e2.66, respectively, throughout follow-up. Sixty-six recurrences (12.11%) were diagnosed. Intraoperative complications were nerve root-related (n [ 3) and dural tear (n [ 1). Postoperative complications included numbness (n [ 18), weakness (n [ 5), and residual disc (n [ 1). No infections or hematomas were reported. CONCLUSIONS: Fully endoscopic interlaminar lumbar discectomy is a safe, effective option for treating lumbar disc herniation, with a long recurrence-free recovery.
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INTRODUCTION
H
erniated nucleus pulposus of the lumbar spine, at a reported prevalence of 1%e3%, is the most common pathological process leading to spine surgery.1 Minimally invasive techniques and technology have been developed to provide access to the disc with better visualization while causing less muscle trauma and its consequences.2,3 Nonetheless, these techniques require special skills, with an extended learning curve. Percutaneous endoscopic lumbar discectomy reportedly is associated with fewer complications and a faster recovery rate compared with standard open discectomy. The transforaminal approach was developed first and was reported to give excellent results in terms of nerve root decompression, but it is associated
From the 1Spine Institute, Bumrungrad International Hospital, Bangkok; 2School of Orthopedics, Institute of Medicine, Suranaree University of Technology, Nakhon Ratchasima; 3Bumrungrad Research Center, Bumrungrad International Hospital, Bangkok; 4Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand; 5Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA; and 6Center for Spine Surgery and Pain Therapy, Center for Orthopedics and Traumatology of the St. Elisabeth GroupeCatholic Hospital Rhein-Ruhr, St. Anna Hospital Herne/Marien Hospital Herne University Hospital of the Ruhr University of Bochum/Marien Hospital Witten, Herne, Germany To whom correspondence should be addressed: Krit Pongpirul, M.D., M.P.H., Ph.D. [E-mail: [email protected]] Citation: World Neurosurg. (2019). https://doi.org/10.1016/j.wneu.2019.07.101 Journal homepage: www.journals.elsevier.com/world-neurosurgery Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2019 Elsevier Inc. All rights reserved.
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ORIGINAL ARTICLE KANTHIKA WASINPONGWANICH ET AL.
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Table 1. Reports on Full Endoscopic Interlaminar Lumbar Discectomy Number of Patients
Outcomes
Retrospective, observational
50
Operative time, hospital stay, modified MacNab criteria, VAS scores
China
Retrospective, observational
479
Descriptions of the types, incidences, and characteristics of complications following FEILD effectiveness of preventive and treatment measures
Tonosu et al., 20168
Japan
Randomized controlled trial
41
Mean recovery rate of mJOA score
Li et al., 2016
China
Retrospective, observational
60
Operative time, blood loss, removed disc tissue volume, LOS, VAS, ODI, and MacNab criteria results for clinical curative effectiveness at 12 months
Nie et al., 2016
China
Randomized controlled trial
60 (30/group)
ODI, VAS, and modified MacNab criteria: operation time, radiation time, postoperative bed time, hospital LOS
Passacantilli et al., 20159
Italy
Retrospective, observational
100
ODI and VAS (leg and back) at discharge, 3 months, 6 months, and 2 years
Li et al., 20153
China
Retrospective, observational
72
Operative time, blood loss, LOS, and complications; rate of conversion to open procedure; VAS-evaluated preoperative and postoperative clinical results
Xu et al., 2014
China
Retrospective, observational
36
Perioperative parameters (operative duration, intraoperative blood loss, extent of intraoperative bone/ligament excision), clinical curative effect index [VAS] score for leg and back pain, complications, rate of conversion to open surgery; groups A, B, and C assigned by study time of surgeons
Choi et al., 201310
Korea
Preoperative and postoperative, observational
60 (30/group)
Preoperative and postoperative radiologic assessments of disc type, size, height, location, migration; foraminal height; iliolumbar angle; iliac height; interlaminar space. Clinical data compared with those at a 2-year follow-up Also, preoperative and postoperative pain (via VAS and ODI) and time to return to work
Wang et al., 201211
China
Retrospective case series
50
Starting point of the nerve root at the dura endoscopically—classified according to the level of the incision of the ligament flavum—as type I (starting point of the nerve root was higher than the incision) or type II (starting point was lower than the incision). Causes of and effective prophylactic measurements for conversion to open surgery
Wang et al., 201112
China
Prospective, observational
30 (10/groups)
Operative time, LOS, VAS (leg and back) pain scores, complications, rate of conversion to open surgery
Choi et al., 20064
Korea
Retrospective, observational
67
VAS, ODI
Study
Country
Study Design
Nakamura and Yoshihara, 20171
Japan
Xie et al., 20177
FEILD, full endoscopic interlaminar lumbar discectomy; mJOA, mean Japanese Orthopedic Association; LOS, length of stay; MRI, magnetic resonance imaging; ODI, Oswestry Disability Index; RCT, randomized controlled trial; VAS, visual analog scale.
with some anatomic constraints in patients with lower lumbar disc level involvement and even in some with involvement of the upper lumbar level.4 Although endoscopy-assisted interlaminar procedures were reported in the late 1990s,5 interlaminar full endoscopic lumbar discectomy became more popular after Ruetten et al.6 introduced it in 2007 (Table 1). Numerous studies have reported a good success rate with the interlaminar approach.3,4,6-11,13 Most studies reported the complications associated with the interlaminar approach to percutaneous discectomy separately from clinical outcomes.5,14 The incidence of complications varies markedly among studies with various sample sizes.3-9,13-15 Some studies have noted that the learning curve plays an important role in decreasing complications.2,14 To the best of our knowledge, published evidence of clinical outcomes and complications of the interlaminar technique is limited. In 2009, preliminary clinical outcomes and
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complications were reported in 48 Thai patients who underwent full endoscopic interlaminar lumbar discectomy (FEILD) in 2 spine centers.16 The purpose of the present study was to evaluate clinical outcomes and complications based on our incremental experience with FEILD in a sufficient number of patients to make the results relevant. Our institution includes international hospitals, and thus our sample comprises multiethnic patients, which could introduce a variety of results with this technique. METHODS At our spine institution, we perform full endoscopic discectomy for lumbar herniated nucleus pulposus using an interlaminar, transforaminal, or extraforaminal approach, depending on the site of the herniation. This study included all patients age >18 years diagnosed with lumbar herniated nucleus pulposus who
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ORIGINAL ARTICLE KANTHIKA WASINPONGWANICH ET AL.
FULL-ENDOSCOPIC INTERLAMINAR LUMBAR DISCECTOMY
underwent FEILD at our institution between January 1, 2011, and December 31, 2016. Exclusion criteria were a diagnosis of discitis, recent spinal fracture, and radiographically proven instability. Altogether, 545 patients (with a total of 559 procedures) were included in this study. The FEILD technique involves intradiscal removal of the unhealthy disc and radiofrequency coagulation of the healthy remaining disc. All the patients were operated on by the same surgeon and were followed up by the same spine surgical team, supervised by the same surgeon. All data were retrospectively reviewed from the patients’ medical records. Incomplete or missing data were obtained by phone call and/or e-mail. The clinical data were retrieved from the patients’ medical records. The preoperative and postoperative data (i.e., clinical outcomes) were assessed using the Oswestry Disability Index (ODI), visual analog scale (VAS) for back pain, and VAS for leg pain at 1 week and 3 and 6 months postoperatively and yearly thereafter. The time to recurrence (if present) was recorded in months. Complications were recorded from the medical records and classified as intraoperative complications (e.g., nerve root injury, dural tear) or postoperative complications (e.g., numbness, weakness, residual disc, hematoma, infection). Surgical Procedure Under general anesthesia and intravenous antibiotic prophylaxis, the patient is positioned with both hips and knees in flexion. (The interlaminar window can be opened more widely in this position.) An 0.8-cm incision is made near the midline on the operated interlaminar window via an anteroposterior fluoroscopic view (Figure 1). The dilator is inserted through the fascia, followed by an endoscopic working sleeve aimed over the ligamentum flavum. The paravertebral muscle is coagulated to identify the border of the interlaminar window. The ligamentum flavum is then cut in a mediolateral direction at the level of the tip of the descending facet. The working sleeve is passed through the cut ligament flavum into the epidural space, with the beveled tip placed on the remaining facet (Figure 2). The epidural tissue covering the lateral rim of the dural sac and exiting nerve root is gently removed using a pituitary rongeur. The working sleeve is rotated to retract the exiting nerve root medially. The posterior longitudinal ligament (PLL) is cut using a micropunch in the mediolateral direction, and the free fragments are removed (Figures 3 and 4). A probe is to identify the annular tear and trace the sequestered disc. The border of the annular defect and intradiscal area is diminished by Trigger-Flex coagulation (Figures 5 and 6). The entire passage of the exiting nerve root is evaluated under visualization for pulsation and tightness. Methylprednisolone suspension (40 mg; Depo-Medrol, Pharmacia & Upjohn, Kalamazoo, Michigan, USA) is applied to the epidural space, and the subcuticular layer of the skin is then sutured. Statistical Analysis Patients’ demographic data, clinical characteristics, and complication rates were analyzed using descriptive statistics. VAS scores were analyzed preoperatively and 1 week postoperatively using Student’s paired t test. VAS and ODI scores were analyzed preoperatively and 3 months postoperatively using Student’s paired
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Figure 1. A probe was used to identify the near midline of the index interlaminar window under fluoroscopy.
t test. Improvement was analyzed with the VAS scores at 1 week and 3 months postoperatively. The VAS and ODI scores across ethnicities were analyzed using 1-way analysis of variance. Survival analysis and KaplaneMeier plots were applied to explore differential recurrences across ethnicities. The number of months between the operation and recurrence was applied as time-toevent data. A Cox proportional hazard model was used to analyze the hazard ratio.
Figure 2. The ligamentum flavum (:) was cut with a punch in a slit-like fashion.
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FULL-ENDOSCOPIC INTERLAMINAR LUMBAR DISCECTOMY
Figure 3. The cut ligamentum flavum (:), herniated disc (+), and compressed nerve root were visualized.
Figure 5. Under nerve root retraction by a working sleeve, the borders of annular defect were explored, and coagulation was performed on all borders as well as intradiscally.
RESULTS Patients’ Demographic and Clinical Characteristics The patients (34.43% female; average age, 46.44 years) had a mean body mass index (BMI) of 27 kg/m2. Most of the patients (n ¼ 531)
Figure 4. After gentle removal of the epidural tissue, the herniated disc (+) was identified and removed, Ligamentum flavum (:).
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required surgery at only a single level. The affected levels were L2-3 in 1.47% of patients, L3-4 in 6.96%, L4-5 in 49.45%, and L5-S1 in 44.69%. Two-level operations were performed in 1 patient
Figure 6. The cut ligamentum flavum (-), annular defect (:), and relaxed nerve root after completion of the procedure.
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ORIGINAL ARTICLE KANTHIKA WASINPONGWANICH ET AL.
FULL-ENDOSCOPIC INTERLAMINAR LUMBAR DISCECTOMY
Table 2. Clinical Outcomes Outcome
Preoperative
1 Week
3 Months
6 Months
1 Year
2 Years
3 Years
4 Years
Final Follow-Up
4.99
1.67
1.88
2.25
2.56
2.65
3.14
2.19
2.83
VAS leg, mean
5.70
1.81
1.57
2.14
2.41
2.11
2.66
1.19
3.83
ODI, %, mean
42.76
N/A
15.59
18.00
18.00
17.00
15.00
15.00
14.00
VAS back, mean
VAS, visual analog scale; ODI, Oswestry Disability Index; N/A, not applicable.
at L3-4 and L4-5, in 1 patient at L3-4 and L5-S1, and in 12 patients at L4-5 to L5-S1. Annular defect size was recorded as small (1e5 mm) in 157 cases, medium (5e10 mm) in 177 cases, and large (>10 mm) in 94 cases. In addition, 57 cases were recorded as not having a defect. All patients underwent successful FEILD, with no conversions to microscopic discectomy or open surgery. Among the 545 patients, 66 (12.11%) were diagnosed with recurrent herniation. The treatment for such recurrence was either conservative or surgical. In this study, only 7.30% of the patients who underwent FEILD required a second operation. Intraoperative complications included nerve root injury (3 cases; 0.55%) and dural tear (1 case; 0.18%). Postoperative complications included numbness (18 cases, 3.3%), weakness (5 cases; 0.92%), and residual disc (1 case; 0.18%). No infections or hematomas were reported. Clinical Outcomes The mean VAS scores for back and leg pain preoperatively and at 1 week, 3 and 6 months, and 1, 2, 3, and 4 years postoperatively and the final follow-up were 4.99, 1.67, 1.88, 2.25, 2.56, 2.65, 3.14, 2.19, and 2.83 and 5.70, 1.81, 1.57, 2.14, 2.41, 2.11, 2.66, 1.19, and 3.83, respectively. The postoperative VAS pain scores for both back and leg pain at 1 week (P < 0.01 for both) and 3 months (P < 0.01 for both) improved significantly compared with those before surgery. The mean ODI values preoperatively and at 1 week, 3 and 6 months, and 1, 2, 3, and 4 years postoperatively and the final follow-up were 42.76%, 15.59%, 15.00%, 17.00%, 15.00%, 15.00%, and 14.00%, respectively. The postoperative mean ODI was significantly improved at 3 months compared with its preoperative value (P < 0.01) (Table 2). There were no differentiating characteristics across ethnicities regarding recurrence. The median time to recurrence was 46.33 months (Figure 7).
discectomy caused less muscle damage while allowing sufficient disc removal. The incidence of reoperation was similar to that found in a meta-analysis that reported an incidence of 7.46% in the fully endoscopic group.3 In our study, 7.30% of patients required a second surgery after fully endoscopic discectomy. The median time to recurrence was 46.33 months, compared with 5 months in the study of Yao et al.,23 which used a transforaminal approach. In addition, Yao et al.,23 in a descriptive analysis, suggested obesity and older age as strong risk factors for recurrence after endoscopic discectomy. However, given the BMI cutoff point of 25.0 kg/m2, our survival analysis showed similar recurrence rates in patients with high BMI and those with low BMI. Although older age (>50 years) was a risk factor, there was no correlation of age with time to recurrence. Furthermore, our survival analysis showed no correlation of time to recurrence across ethnicities, BMI, or the size of the annular defect. Further studies of risk factors may be needed to explain recurrences following endoscopic discectomy. In our cohort, there were three nerve root injuries (0.55%), two of which were caused by anatomic variations.11 The 3.30% incidence of numbness in this study was found acceptable compared with that in other studies, which varied from 0 to 17.88%.3,4,8,9,15,18 The reported rate of dural injury ranges from 0.81% to 4.00%.4,9,13,15 Some resulted in cerebrospinal fluid leakage or nerve pain symptoms (burning, itching, and shooting pain).13
DISCUSSION FEILD with the transforaminal approach has provided satisfactory outcomes, whereas supporting evidence of the interlaminar approach has been limited to a single case series.17 Furthermore, previous studies focused only on patients from the authors’ home countries,2-4,6-13,15,16,18-23 and only a few studies included multiple ethnicities. Thus, we believe that the present study is relatively unique in analyzing the clinical outcomes and complications of FEILD in an adequate international sample. Similar to the aforementioned studies, in the present study, clinical outcomes (VAS back pain and leg pain scores, ODI) improved significantly after FEILD surgery. The fully endoscopic
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Figure 7. KaplaneMeier survival analysis of recurrence by ethnicity.
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We had only 1 case of a dural tear (0.18%), occurring in a patient who had undergone a previous microdiscectomy resulted in no nerve pain symptoms, and the minimal cerebrospinal fluid leakage resolved after 48 hours of bed rest. Tonosu et al.8 reported transient muscular weakness in 2.43% of their patients with shoulder-type disc herniation. Similarly, Sencer et al.13 reported a 3.0% incidence of transient weakness in their comparison study of interlaminar and transforaminal discectomy. In our study, there were 5 cases of weakness (0.92%), including 3 of minor weakness (grade VeIVþ), possibly related to variations in the examiners’ assessments, 1 case of extensor hallucis longus weakness of grade VeIII, and 1 case of tibialis anterior weakness of grade VeIV. In the latter 2 patients, the weakness was temporary and resolved within a month. In 1 of these patients, the herniated disc was considered large with a calcified part, and in the other patient, identifying the fragment was difficult. We suspect that these cases of temporary weaknesses were related to prolonged intraoperative nerve retraction.5,22 Our surgical technique included cautious, gentle pressing of the working sleeve tip against the intervertebral disc and rotating the sheath to retract the nerve root away, thereby minimizing the time taken to retract the nerve. This technique has a learning curve, however. The cases of residual disc in this study was due to a large calcified herniated disc. The surgeon was unable to remove all of the calcified material and thus performed a sequestrectomy, which led to temporary muscular weakness. We found none of the other complications reported in other studies, such as bladder or rectal
REFERENCES 1. Nakamura JI, Yoshihara K. Initial clinical outcomes of percutaneous full-endoscopic lumbar discectomy using an interlaminar approach at the L4-L5. Pain Physician. 2017;20:E507-E512. 2. Feng F, Xu Q, Yan F, et al. Comparison of 7 surgical interventions for lumbar disc herniation: a network meta-analysis. Pain Physician. 2017;20: E863-E871. 3. Li ZZ, Hou SX, Shang WL, Song KR, Zhao HL. The strategy and early clinical outcome of fullendoscopic L5/S1 discectomy through interlaminar approach. Clin Neurol Neurosurg. 2015;133: 40-45. 4. Choi G, Lee SH, Raiturker PP, Lee S, Chae YS. Percutaneous endoscopic interlaminar discectomy for intracanalicular disc herniations at L5-S1 using a rigid working channel endoscope. Neurosurgery. 2006;58(1 suppl):ONS59-ONS68 [discussion: ONS59-ONS68]. 5. Yörüko glu AG, Göker B, Tahta A, et al. Fully endoscopic interlaminar and transforaminal lumbar discectomy: analysis of 47 complications encountered in a series of 835 patients. Neurocirugia (Astur). 2017;28:235-241. 6. Ruetten S, Komp M, Merk H, Godolias G. Fullendoscopic interlaminar and transforaminal lumbar discectomy versus conventional microsurgical technique: a prospective, randomized,
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dysfunction,8,21 conversion to open surgery,8,21 convulsions,15 hematoma,14 or sympathetically mediated pain syndrome.14 The same surgical team experienced 1 conversion to open surgery among early cases.15 We recommend more careful consideration of the patient’s anatomy in recurrent cases, especially after open surgery. We recommend working as quickly as possible when using the sheath to retract the nerve root, and when using the radiofrequency device, applying the tip intermittently and briefly to coagulate the epidural tissue around the nerve root. Because we are sometimes unable to identify the calcified part on magnetic resonance imaging, we consider performing a computed tomography scan in patients in whom a calcified disc is suspected (e.g., a patient with a long history of symptoms). Further studies of risk factors may be needed to explain recurrences after endoscopic discectomy. Limitations of this study include its retrospective design. In addition, we were unable to discount the subjectivity of the physical examinations. CONCLUSIONS Based on our present findings, we consider FEILD to be a safe, effective option for treating lumbar disc herniation. ACKNOWLEDGMENTS We thank Nancy Schatken, BS, MT (ASCP), from the Edanz Group (www.edanzediting.com/ac), for editing a draft of this manuscript.
controlled study. Spine (Phila Pa 1976). 2008;33: 931-939. 7. Xie TH, Zeng JC, Li ZH, et al. Complications of lumbar disc herniation following full-endoscopic interlaminar lumbar discectomy: a large, singlecenter, retrospective study. Pain Physician. 2017;20: E379-E387. 8. Tonosu J, Oshima Y, Shiboi R, et al. Consideration of proper operative route for interlaminar approach for percutaneous endoscopic lumbar discectomy. J Spine Surg. 2016;2:281-288. 9. Passacantilli E, Lenzi J, Caporlingua F, et al. Endoscopic interlaminar approach for intracanal L5-S1 disc herniation: classification of disc prolapse in relation to learning curve and surgical outcome. Asian J Endosc Surg. 2015;8:445-453. 10. Choi KC, Kim JS, Ryu KS, Kang BU, Ahn Y, Lee SH. Percutaneous endoscopic lumbar discectomy for L5-S1 disc herniation: transforaminal versus interlaminar approach. Pain Physician. 2013; 16:547-556. 11. Wang B, Lü G, Liu W, Cheng I, Patel AA. Fullendoscopic interlaminar approach for the surgical treatment of lumbar disc herniation: the causes and prophylaxis of conversion to open. Arch Orthop Trauma Surg. 2012;132:1531-1538. 12. Wang B, Lü G, Patel AA, Ren P, Cheng I. An evaluation of the learning curve for a complex surgical technique: the full endoscopic interlaminar approach for lumbar disc herniations. Spine J. 2011;11:122-130.
13. Sencer A, Yorukoglu AG, Akcakaya MO, et al. Fully endoscopic interlaminar and transforaminal lumbar discectomy: short-term clinical results of 163 surgically treated patients. World Neurosurg. 2014; 82:884-890. 14. Zhou C, Zhang G, Panchal RR, et al. Unique complications of percutaneous endoscopic lumbar discectomy and percutaneous endoscopic interlaminar discectomy. Pain Physician. 2018;21: E105-E112. 15. Chen HT, Tsai CH, Chao SC, et al. Endoscopic discectomy of L5-S1 disc herniation via an interlaminar approach: prospective controlled study under local and general anesthesia. Surg Neurol Int. 2011;2:93. 16. Kuonsongtum V, Paiboonsirijit S, Kesornsak W, et al. Result of full endoscopic uniportal lumbar discectomy: preliminary report. J Med Assoc Thai. 2009;92:776-780. 17. Shi C, Kong W, Liao W, et al. The early clinical outcomes of a percutaneous full-endoscopic interlaminar approach via a surrounding nerve root discectomy operative route for the treatment of ventral-type lumbar disc herniation. Biomed Res Int. 2018;2018:9157089. 18. Ahn Y, Lee SH, Park WM, Lee HY, Shin SW, Kang HY. Percutaneous endoscopic lumbar discectomy for recurrent disc herniation: surgical technique, outcome, and prognostic factors of 43 consecutive cases. Spine (Phila Pa 1976). 2004;29: E326-E332.
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FULL-ENDOSCOPIC INTERLAMINAR LUMBAR DISCECTOMY
19. Choi KC, Lee JH, Kim JS, et al. Unsuccessful percutaneous endoscopic lumbar discectomy: a single-center experience of 10,228 cases. Neurosurgery. 2015;76:372-380 [discussion: 380-381; quiz 381].
22. Wu J, Zhang C, Zheng W, Hong CS, Li C, Zhou Y. Analysis of the characteristics and clinical outcomes of percutaneous endoscopic lumbar discectomy for upper lumbar disc herniation. World Neurosurg. 2016;92:142-147.
20. Eun SS, Lee SH, Sabal LA. Long-term follow-up results of percutaneous endoscopic lumbar discectomy. Pain Physician. 2016;19:E1161-E1166.
23. Yao Y, Liu H, Zhang H, et al. Risk factors for recurrent herniation after percutaneous endoscopic lumbar discectomy. World Neurosurg. 2017; 100:1-6.
21. Kamson S, Trescot AM, Sampson PD, Zhang Y. Full-endoscopic assisted lumbar decompressive surgery performed in an outpatient, ambulatory facility: report of 5 years of complications and risk factors. Pain Physician. 2017;20:E221-E231.
commercial or financial relationships that could be construed as a potential conflict of interest. Received 12 April 2019; accepted 11 July 2019 Citation: World Neurosurg. (2019). https://doi.org/10.1016/j.wneu.2019.07.101 Journal homepage: www.journals.elsevier.com/worldneurosurgery Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2019 Elsevier Inc. All rights reserved.
Conflict of interest statement: The authors declare that the article content was composed in the absence of any
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Full-Endoscopic Interlaminar Lumbar Discectomy: Retrospective Review of Clinical Results and Complications in 545 International Patients Kanthika Wasinpongwanich1,2, Krit Pongpirul3-5, Khin Myat Myat Lwin1, Withawin Kesornsak1, Verapan Kuansongtham1, Sebastian Ruetten6
BACKGROUND: Minimally invasive techniques have been developed to provide access to the disc with better visualization while causing less muscle trauma and its consequences. This study was aimed at evaluating the clinical outcomes and complications of the fully endoscopic lumbar discectomy interlaminar approach in a large number of patients.
-
METHODS: Patients diagnosed with lumbar herniated nucleus pulposus who underwent fully endoscopic interlaminar lumbar discectomy between 2011 and 2016 were reviewed. Perioperative data, preoperative and postoperative Oswestry Disability Index (ODI) scores, visual analog scale (VAS) back pain scores, VAS leg pain scores, and complications were evaluated and recorded at 1 week and 3 and 6 months postoperatively and each year thereafter.
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RESULTS: The study cohort comprised 545 patients (average age, 46.43 years; 34.31% female). The affected levels were L2-3 in 1.47%, L3-4 in 6.96%, L4-5 in 49.45%, and L5-S1 in 44.69%. Mean preoperative ODI, VAS back pain score, and VAS leg pain score were 43.00%, 5.00, and 5.69, respectively. Postoperative ODI at 1 month was reduced to 15.59% and remained within a range of 14.83%18.32% throughout follow-up. Postoperative VAS back and leg pain score results at 1 week were decreased to 1.66 and 1.79, respectively, and remained at 1.89e3.14
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Key words Endoscopic discectomy - Full endoscopic lumbar discectomy - Herniated nucleus pulposus - Interlaminar discectomy - Lumbar disc herniation - Lumbar discectomy - Percutaneous endoscopic discectomy -
Abbreviations and Acronyms FEILD: Fully endoscopic interlaminar lumbar discectomy ODI: Oswestry Disability Index PPL: Posterior longitudinal ligament VAS: Visual analog scale
and 1.59e2.66, respectively, throughout follow-up. Sixty-six recurrences (12.11%) were diagnosed. Intraoperative complications were nerve root-related (n [ 3) and dural tear (n [ 1). Postoperative complications included numbness (n [ 18), weakness (n [ 5), and residual disc (n [ 1). No infections or hematomas were reported. CONCLUSIONS: Fully endoscopic interlaminar lumbar discectomy is a safe, effective option for treating lumbar disc herniation, with a long recurrence-free recovery.
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INTRODUCTION
H
erniated nucleus pulposus of the lumbar spine, at a reported prevalence of 1%e3%, is the most common pathological process leading to spine surgery.1 Minimally invasive techniques and technology have been developed to provide access to the disc with better visualization while causing less muscle trauma and its consequences.2,3 Nonetheless, these techniques require special skills, with an extended learning curve. Percutaneous endoscopic lumbar discectomy reportedly is associated with fewer complications and a faster recovery rate compared with standard open discectomy. The transforaminal approach was developed first and was reported to give excellent results in terms of nerve root decompression, but it is associated
From the 1Spine Institute, Bumrungrad International Hospital, Bangkok; 2School of Orthopedics, Institute of Medicine, Suranaree University of Technology, Nakhon Ratchasima; 3Bumrungrad Research Center, Bumrungrad International Hospital, Bangkok; 4Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand; 5Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA; and 6Center for Spine Surgery and Pain Therapy, Center for Orthopedics and Traumatology of the St. Elisabeth GroupeCatholic Hospital Rhein-Ruhr, St. Anna Hospital Herne/Marien Hospital Herne University Hospital of the Ruhr University of Bochum/Marien Hospital Witten, Herne, Germany To whom correspondence should be addressed: Krit Pongpirul, M.D., M.P.H., Ph.D. [E-mail: [email protected]] Citation: World Neurosurg. (2019). https://doi.org/10.1016/j.wneu.2019.07.101 Journal homepage: www.journals.elsevier.com/world-neurosurgery Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2019 Elsevier Inc. All rights reserved.
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FULL-ENDOSCOPIC INTERLAMINAR LUMBAR DISCECTOMY
Table 1. Reports on Full Endoscopic Interlaminar Lumbar Discectomy Number of Patients
Outcomes
Retrospective, observational
50
Operative time, hospital stay, modified MacNab criteria, VAS scores
China
Retrospective, observational
479
Descriptions of the types, incidences, and characteristics of complications following FEILD effectiveness of preventive and treatment measures
Tonosu et al., 20168
Japan
Randomized controlled trial
41
Mean recovery rate of mJOA score
Li et al., 2016
China
Retrospective, observational
60
Operative time, blood loss, removed disc tissue volume, LOS, VAS, ODI, and MacNab criteria results for clinical curative effectiveness at 12 months
Nie et al., 2016
China
Randomized controlled trial
60 (30/group)
ODI, VAS, and modified MacNab criteria: operation time, radiation time, postoperative bed time, hospital LOS
Passacantilli et al., 20159
Italy
Retrospective, observational
100
ODI and VAS (leg and back) at discharge, 3 months, 6 months, and 2 years
Li et al., 20153
China
Retrospective, observational
72
Operative time, blood loss, LOS, and complications; rate of conversion to open procedure; VAS-evaluated preoperative and postoperative clinical results
Xu et al., 2014
China
Retrospective, observational
36
Perioperative parameters (operative duration, intraoperative blood loss, extent of intraoperative bone/ligament excision), clinical curative effect index [VAS] score for leg and back pain, complications, rate of conversion to open surgery; groups A, B, and C assigned by study time of surgeons
Choi et al., 201310
Korea
Preoperative and postoperative, observational
60 (30/group)
Preoperative and postoperative radiologic assessments of disc type, size, height, location, migration; foraminal height; iliolumbar angle; iliac height; interlaminar space. Clinical data compared with those at a 2-year follow-up Also, preoperative and postoperative pain (via VAS and ODI) and time to return to work
Wang et al., 201211
China
Retrospective case series
50
Starting point of the nerve root at the dura endoscopically—classified according to the level of the incision of the ligament flavum—as type I (starting point of the nerve root was higher than the incision) or type II (starting point was lower than the incision). Causes of and effective prophylactic measurements for conversion to open surgery
Wang et al., 201112
China
Prospective, observational
30 (10/groups)
Operative time, LOS, VAS (leg and back) pain scores, complications, rate of conversion to open surgery
Choi et al., 20064
Korea
Retrospective, observational
67
VAS, ODI
Study
Country
Study Design
Nakamura and Yoshihara, 20171
Japan
Xie et al., 20177
FEILD, full endoscopic interlaminar lumbar discectomy; mJOA, mean Japanese Orthopedic Association; LOS, length of stay; MRI, magnetic resonance imaging; ODI, Oswestry Disability Index; RCT, randomized controlled trial; VAS, visual analog scale.
with some anatomic constraints in patients with lower lumbar disc level involvement and even in some with involvement of the upper lumbar level.4 Although endoscopy-assisted interlaminar procedures were reported in the late 1990s,5 interlaminar full endoscopic lumbar discectomy became more popular after Ruetten et al.6 introduced it in 2007 (Table 1). Numerous studies have reported a good success rate with the interlaminar approach.3,4,6-11,13 Most studies reported the complications associated with the interlaminar approach to percutaneous discectomy separately from clinical outcomes.5,14 The incidence of complications varies markedly among studies with various sample sizes.3-9,13-15 Some studies have noted that the learning curve plays an important role in decreasing complications.2,14 To the best of our knowledge, published evidence of clinical outcomes and complications of the interlaminar technique is limited. In 2009, preliminary clinical outcomes and
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complications were reported in 48 Thai patients who underwent full endoscopic interlaminar lumbar discectomy (FEILD) in 2 spine centers.16 The purpose of the present study was to evaluate clinical outcomes and complications based on our incremental experience with FEILD in a sufficient number of patients to make the results relevant. Our institution includes international hospitals, and thus our sample comprises multiethnic patients, which could introduce a variety of results with this technique. METHODS At our spine institution, we perform full endoscopic discectomy for lumbar herniated nucleus pulposus using an interlaminar, transforaminal, or extraforaminal approach, depending on the site of the herniation. This study included all patients age >18 years diagnosed with lumbar herniated nucleus pulposus who
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ORIGINAL ARTICLE KANTHIKA WASINPONGWANICH ET AL.
FULL-ENDOSCOPIC INTERLAMINAR LUMBAR DISCECTOMY
underwent FEILD at our institution between January 1, 2011, and December 31, 2016. Exclusion criteria were a diagnosis of discitis, recent spinal fracture, and radiographically proven instability. Altogether, 545 patients (with a total of 559 procedures) were included in this study. The FEILD technique involves intradiscal removal of the unhealthy disc and radiofrequency coagulation of the healthy remaining disc. All the patients were operated on by the same surgeon and were followed up by the same spine surgical team, supervised by the same surgeon. All data were retrospectively reviewed from the patients’ medical records. Incomplete or missing data were obtained by phone call and/or e-mail. The clinical data were retrieved from the patients’ medical records. The preoperative and postoperative data (i.e., clinical outcomes) were assessed using the Oswestry Disability Index (ODI), visual analog scale (VAS) for back pain, and VAS for leg pain at 1 week and 3 and 6 months postoperatively and yearly thereafter. The time to recurrence (if present) was recorded in months. Complications were recorded from the medical records and classified as intraoperative complications (e.g., nerve root injury, dural tear) or postoperative complications (e.g., numbness, weakness, residual disc, hematoma, infection). Surgical Procedure Under general anesthesia and intravenous antibiotic prophylaxis, the patient is positioned with both hips and knees in flexion. (The interlaminar window can be opened more widely in this position.) An 0.8-cm incision is made near the midline on the operated interlaminar window via an anteroposterior fluoroscopic view (Figure 1). The dilator is inserted through the fascia, followed by an endoscopic working sleeve aimed over the ligamentum flavum. The paravertebral muscle is coagulated to identify the border of the interlaminar window. The ligamentum flavum is then cut in a mediolateral direction at the level of the tip of the descending facet. The working sleeve is passed through the cut ligament flavum into the epidural space, with the beveled tip placed on the remaining facet (Figure 2). The epidural tissue covering the lateral rim of the dural sac and exiting nerve root is gently removed using a pituitary rongeur. The working sleeve is rotated to retract the exiting nerve root medially. The posterior longitudinal ligament (PLL) is cut using a micropunch in the mediolateral direction, and the free fragments are removed (Figures 3 and 4). A probe is to identify the annular tear and trace the sequestered disc. The border of the annular defect and intradiscal area is diminished by Trigger-Flex coagulation (Figures 5 and 6). The entire passage of the exiting nerve root is evaluated under visualization for pulsation and tightness. Methylprednisolone suspension (40 mg; Depo-Medrol, Pharmacia & Upjohn, Kalamazoo, Michigan, USA) is applied to the epidural space, and the subcuticular layer of the skin is then sutured. Statistical Analysis Patients’ demographic data, clinical characteristics, and complication rates were analyzed using descriptive statistics. VAS scores were analyzed preoperatively and 1 week postoperatively using Student’s paired t test. VAS and ODI scores were analyzed preoperatively and 3 months postoperatively using Student’s paired
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Figure 1. A probe was used to identify the near midline of the index interlaminar window under fluoroscopy.
t test. Improvement was analyzed with the VAS scores at 1 week and 3 months postoperatively. The VAS and ODI scores across ethnicities were analyzed using 1-way analysis of variance. Survival analysis and KaplaneMeier plots were applied to explore differential recurrences across ethnicities. The number of months between the operation and recurrence was applied as time-toevent data. A Cox proportional hazard model was used to analyze the hazard ratio.
Figure 2. The ligamentum flavum (:) was cut with a punch in a slit-like fashion.
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ORIGINAL ARTICLE KANTHIKA WASINPONGWANICH ET AL.
FULL-ENDOSCOPIC INTERLAMINAR LUMBAR DISCECTOMY
Figure 3. The cut ligamentum flavum (:), herniated disc (+), and compressed nerve root were visualized.
Figure 5. Under nerve root retraction by a working sleeve, the borders of annular defect were explored, and coagulation was performed on all borders as well as intradiscally.
RESULTS Patients’ Demographic and Clinical Characteristics The patients (34.43% female; average age, 46.44 years) had a mean body mass index (BMI) of 27 kg/m2. Most of the patients (n ¼ 531)
Figure 4. After gentle removal of the epidural tissue, the herniated disc (+) was identified and removed, Ligamentum flavum (:).
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required surgery at only a single level. The affected levels were L2-3 in 1.47% of patients, L3-4 in 6.96%, L4-5 in 49.45%, and L5-S1 in 44.69%. Two-level operations were performed in 1 patient
Figure 6. The cut ligamentum flavum (-), annular defect (:), and relaxed nerve root after completion of the procedure.
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ORIGINAL ARTICLE KANTHIKA WASINPONGWANICH ET AL.
FULL-ENDOSCOPIC INTERLAMINAR LUMBAR DISCECTOMY
Table 2. Clinical Outcomes Outcome
Preoperative
1 Week
3 Months
6 Months
1 Year
2 Years
3 Years
4 Years
Final Follow-Up
4.99
1.67
1.88
2.25
2.56
2.65
3.14
2.19
2.83
VAS leg, mean
5.70
1.81
1.57
2.14
2.41
2.11
2.66
1.19
3.83
ODI, %, mean
42.76
N/A
15.59
18.00
18.00
17.00
15.00
15.00
14.00
VAS back, mean
VAS, visual analog scale; ODI, Oswestry Disability Index; N/A, not applicable.
at L3-4 and L4-5, in 1 patient at L3-4 and L5-S1, and in 12 patients at L4-5 to L5-S1. Annular defect size was recorded as small (1e5 mm) in 157 cases, medium (5e10 mm) in 177 cases, and large (>10 mm) in 94 cases. In addition, 57 cases were recorded as not having a defect. All patients underwent successful FEILD, with no conversions to microscopic discectomy or open surgery. Among the 545 patients, 66 (12.11%) were diagnosed with recurrent herniation. The treatment for such recurrence was either conservative or surgical. In this study, only 7.30% of the patients who underwent FEILD required a second operation. Intraoperative complications included nerve root injury (3 cases; 0.55%) and dural tear (1 case; 0.18%). Postoperative complications included numbness (18 cases, 3.3%), weakness (5 cases; 0.92%), and residual disc (1 case; 0.18%). No infections or hematomas were reported. Clinical Outcomes The mean VAS scores for back and leg pain preoperatively and at 1 week, 3 and 6 months, and 1, 2, 3, and 4 years postoperatively and the final follow-up were 4.99, 1.67, 1.88, 2.25, 2.56, 2.65, 3.14, 2.19, and 2.83 and 5.70, 1.81, 1.57, 2.14, 2.41, 2.11, 2.66, 1.19, and 3.83, respectively. The postoperative VAS pain scores for both back and leg pain at 1 week (P < 0.01 for both) and 3 months (P < 0.01 for both) improved significantly compared with those before surgery. The mean ODI values preoperatively and at 1 week, 3 and 6 months, and 1, 2, 3, and 4 years postoperatively and the final follow-up were 42.76%, 15.59%, 15.00%, 17.00%, 15.00%, 15.00%, and 14.00%, respectively. The postoperative mean ODI was significantly improved at 3 months compared with its preoperative value (P < 0.01) (Table 2). There were no differentiating characteristics across ethnicities regarding recurrence. The median time to recurrence was 46.33 months (Figure 7).
discectomy caused less muscle damage while allowing sufficient disc removal. The incidence of reoperation was similar to that found in a meta-analysis that reported an incidence of 7.46% in the fully endoscopic group.3 In our study, 7.30% of patients required a second surgery after fully endoscopic discectomy. The median time to recurrence was 46.33 months, compared with 5 months in the study of Yao et al.,23 which used a transforaminal approach. In addition, Yao et al.,23 in a descriptive analysis, suggested obesity and older age as strong risk factors for recurrence after endoscopic discectomy. However, given the BMI cutoff point of 25.0 kg/m2, our survival analysis showed similar recurrence rates in patients with high BMI and those with low BMI. Although older age (>50 years) was a risk factor, there was no correlation of age with time to recurrence. Furthermore, our survival analysis showed no correlation of time to recurrence across ethnicities, BMI, or the size of the annular defect. Further studies of risk factors may be needed to explain recurrences following endoscopic discectomy. In our cohort, there were three nerve root injuries (0.55%), two of which were caused by anatomic variations.11 The 3.30% incidence of numbness in this study was found acceptable compared with that in other studies, which varied from 0 to 17.88%.3,4,8,9,15,18 The reported rate of dural injury ranges from 0.81% to 4.00%.4,9,13,15 Some resulted in cerebrospinal fluid leakage or nerve pain symptoms (burning, itching, and shooting pain).13
DISCUSSION FEILD with the transforaminal approach has provided satisfactory outcomes, whereas supporting evidence of the interlaminar approach has been limited to a single case series.17 Furthermore, previous studies focused only on patients from the authors’ home countries,2-4,6-13,15,16,18-23 and only a few studies included multiple ethnicities. Thus, we believe that the present study is relatively unique in analyzing the clinical outcomes and complications of FEILD in an adequate international sample. Similar to the aforementioned studies, in the present study, clinical outcomes (VAS back pain and leg pain scores, ODI) improved significantly after FEILD surgery. The fully endoscopic
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Figure 7. KaplaneMeier survival analysis of recurrence by ethnicity.
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We had only 1 case of a dural tear (0.18%), occurring in a patient who had undergone a previous microdiscectomy resulted in no nerve pain symptoms, and the minimal cerebrospinal fluid leakage resolved after 48 hours of bed rest. Tonosu et al.8 reported transient muscular weakness in 2.43% of their patients with shoulder-type disc herniation. Similarly, Sencer et al.13 reported a 3.0% incidence of transient weakness in their comparison study of interlaminar and transforaminal discectomy. In our study, there were 5 cases of weakness (0.92%), including 3 of minor weakness (grade VeIVþ), possibly related to variations in the examiners’ assessments, 1 case of extensor hallucis longus weakness of grade VeIII, and 1 case of tibialis anterior weakness of grade VeIV. In the latter 2 patients, the weakness was temporary and resolved within a month. In 1 of these patients, the herniated disc was considered large with a calcified part, and in the other patient, identifying the fragment was difficult. We suspect that these cases of temporary weaknesses were related to prolonged intraoperative nerve retraction.5,22 Our surgical technique included cautious, gentle pressing of the working sleeve tip against the intervertebral disc and rotating the sheath to retract the nerve root away, thereby minimizing the time taken to retract the nerve. This technique has a learning curve, however. The cases of residual disc in this study was due to a large calcified herniated disc. The surgeon was unable to remove all of the calcified material and thus performed a sequestrectomy, which led to temporary muscular weakness. We found none of the other complications reported in other studies, such as bladder or rectal
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dysfunction,8,21 conversion to open surgery,8,21 convulsions,15 hematoma,14 or sympathetically mediated pain syndrome.14 The same surgical team experienced 1 conversion to open surgery among early cases.15 We recommend more careful consideration of the patient’s anatomy in recurrent cases, especially after open surgery. We recommend working as quickly as possible when using the sheath to retract the nerve root, and when using the radiofrequency device, applying the tip intermittently and briefly to coagulate the epidural tissue around the nerve root. Because we are sometimes unable to identify the calcified part on magnetic resonance imaging, we consider performing a computed tomography scan in patients in whom a calcified disc is suspected (e.g., a patient with a long history of symptoms). Further studies of risk factors may be needed to explain recurrences after endoscopic discectomy. Limitations of this study include its retrospective design. In addition, we were unable to discount the subjectivity of the physical examinations. CONCLUSIONS Based on our present findings, we consider FEILD to be a safe, effective option for treating lumbar disc herniation. ACKNOWLEDGMENTS We thank Nancy Schatken, BS, MT (ASCP), from the Edanz Group (www.edanzediting.com/ac), for editing a draft of this manuscript.
controlled study. Spine (Phila Pa 1976). 2008;33: 931-939. 7. Xie TH, Zeng JC, Li ZH, et al. Complications of lumbar disc herniation following full-endoscopic interlaminar lumbar discectomy: a large, singlecenter, retrospective study. Pain Physician. 2017;20: E379-E387. 8. Tonosu J, Oshima Y, Shiboi R, et al. Consideration of proper operative route for interlaminar approach for percutaneous endoscopic lumbar discectomy. J Spine Surg. 2016;2:281-288. 9. Passacantilli E, Lenzi J, Caporlingua F, et al. Endoscopic interlaminar approach for intracanal L5-S1 disc herniation: classification of disc prolapse in relation to learning curve and surgical outcome. Asian J Endosc Surg. 2015;8:445-453. 10. Choi KC, Kim JS, Ryu KS, Kang BU, Ahn Y, Lee SH. Percutaneous endoscopic lumbar discectomy for L5-S1 disc herniation: transforaminal versus interlaminar approach. Pain Physician. 2013; 16:547-556. 11. Wang B, Lü G, Liu W, Cheng I, Patel AA. Fullendoscopic interlaminar approach for the surgical treatment of lumbar disc herniation: the causes and prophylaxis of conversion to open. Arch Orthop Trauma Surg. 2012;132:1531-1538. 12. Wang B, Lü G, Patel AA, Ren P, Cheng I. An evaluation of the learning curve for a complex surgical technique: the full endoscopic interlaminar approach for lumbar disc herniations. Spine J. 2011;11:122-130.
13. Sencer A, Yorukoglu AG, Akcakaya MO, et al. Fully endoscopic interlaminar and transforaminal lumbar discectomy: short-term clinical results of 163 surgically treated patients. World Neurosurg. 2014; 82:884-890. 14. Zhou C, Zhang G, Panchal RR, et al. Unique complications of percutaneous endoscopic lumbar discectomy and percutaneous endoscopic interlaminar discectomy. Pain Physician. 2018;21: E105-E112. 15. Chen HT, Tsai CH, Chao SC, et al. Endoscopic discectomy of L5-S1 disc herniation via an interlaminar approach: prospective controlled study under local and general anesthesia. Surg Neurol Int. 2011;2:93. 16. Kuonsongtum V, Paiboonsirijit S, Kesornsak W, et al. Result of full endoscopic uniportal lumbar discectomy: preliminary report. J Med Assoc Thai. 2009;92:776-780. 17. Shi C, Kong W, Liao W, et al. The early clinical outcomes of a percutaneous full-endoscopic interlaminar approach via a surrounding nerve root discectomy operative route for the treatment of ventral-type lumbar disc herniation. Biomed Res Int. 2018;2018:9157089. 18. Ahn Y, Lee SH, Park WM, Lee HY, Shin SW, Kang HY. Percutaneous endoscopic lumbar discectomy for recurrent disc herniation: surgical technique, outcome, and prognostic factors of 43 consecutive cases. Spine (Phila Pa 1976). 2004;29: E326-E332.
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FULL-ENDOSCOPIC INTERLAMINAR LUMBAR DISCECTOMY
19. Choi KC, Lee JH, Kim JS, et al. Unsuccessful percutaneous endoscopic lumbar discectomy: a single-center experience of 10,228 cases. Neurosurgery. 2015;76:372-380 [discussion: 380-381; quiz 381].
22. Wu J, Zhang C, Zheng W, Hong CS, Li C, Zhou Y. Analysis of the characteristics and clinical outcomes of percutaneous endoscopic lumbar discectomy for upper lumbar disc herniation. World Neurosurg. 2016;92:142-147.
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commercial or financial relationships that could be construed as a potential conflict of interest. Received 12 April 2019; accepted 11 July 2019 Citation: World Neurosurg. (2019). https://doi.org/10.1016/j.wneu.2019.07.101 Journal homepage: www.journals.elsevier.com/worldneurosurgery Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2019 Elsevier Inc. All rights reserved.
Conflict of interest statement: The authors declare that the article content was composed in the absence of any
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