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Application of a narrow-surface cage in full endoscopic minimally invasive transforaminal lumbar interbody fusion
International Journal of Surgery 42 (2017) 83e89
Contents lists available at ScienceDirect
International Journal of Surgery journal homepage: www.journal-surgery.net
Original Research
Application of a narrow-surface cage in full endoscopic minimally invasive transforaminal lumbar interbody fusion Er-xing He, M.D. a, b, *, 1, Jing Guo a, b, 1, Qin-jie Ling a, b, Zhi-xun Yin a, b, Ying Wang a, b, Ming Li a, b a b
Spine Surgery, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, China Guangzhou Orthopaedic Institute, Guangzhou, China
h i g h l i g h t s Endoscopic lumbar interbody fusion still remains a technical challenge. An 8-mm-wide narrow-surface cage was selected for 42 cases underwent endoscopic lumbar interbody fusion. All procedures were performed safely and successfully with minimal trauma and improved visualization. Clinical outcome and fusion rate of narrow-surface cage were acceptable and promising.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 March 2017 Accepted 14 April 2017 Available online 27 April 2017
Background: Spinal endoscopy has been widely applied in lumbar discectomy and decompression. However, endoscopic lumbar interbody fusion still remains a technical challenge due to the limited space within the working trocar for cage implantation. The purpose of this study was to investigate the feasibility and effectiveness of using a narrow-surface fusion cage in full endoscopic minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) for the treatment of lumbar degenerative disease. Materials and Methods: From Jun 2013 to Dec 2014, a total of 42 patients (23 males, 19 females) underwent full endoscopic MIS-TLIF at our hospital was recruited. An 8-mm-wide narrow-surface fusion cage was selected for all cases. Perioperative parameters and complications were recorded. Comparisons on visual analog scale (VAS) and oswestry disability index (ODI) scores before and after surgery were performed. At the last follow-up, Nakai grading system was applied to assess patients' satisfaction; meanwhile, interbody fusion was evaluated by computed tomography. Results: Mean operation time was 233.1 ± 69.5 min, and mean blood loss during surgery was 221.8 ± 98.5 ml. Two patients (4.8%) developed neurological complications. Postoperative follow-up ranged from 24 to 36 months (mean 27.6 ± 3.8 months). VAS and ODI scores were significantly improved 3 months after surgery and at the final follow-up, respectively (P < 0.05). Outcome of surgery was graded as excellent for 32 patients, good for 8 patients, and acceptable for 2 patients, corresponding to a success rate (“good” and “excellent”) of 95.2%. Thirty-nine of the 42 patients demonstrated solid interbody fusion at the last follow-up, indicating a fusion rate of 92.9%. Conclusion: Application of a narrow-surface fusion cage in full endoscopic MIS-TLIF for the treatment of lumbar degenerative disease is feasible and effective. The clinical outcome and fusion success of this procedure were acceptable and promising. © 2017 IJS Publishing Group Ltd. Published by Elsevier Ltd. All rights reserved.
Keywords: Minimally invasive spine surgery Endoscopy Lumbar interbody fusion Fusion cage
1. Introduction
* Corresponding author. Spine Surgery, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, China. E-mail address: [email protected] (E.-x. He). 1 The first two authors contributed equally to this work.
Current endoscopic techniques in spine surgery use varied minimally invasive working trocars to establish the surgical approach, which cause much less trauma to the paraspinal muscle compared with open surgery [1e3]. The endoscope can clearly
http://dx.doi.org/10.1016/j.ijsu.2017.04.053 1743-9191/© 2017 IJS Publishing Group Ltd. Published by Elsevier Ltd. All rights reserved.
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show the fine structures in the deep surgical field and provide excellent visualization [4,5]. Spinal endoscopy has been widely applied in lumbar discectomy and decompression [6e9]. However, reports on endoscopic lumbar interbody fusion are still in paucity. Endoscopic spine surgery differs from open surgery due to the limited space and consequently, requires specialized skills and instruments, especially for fusion cage implantation [5,10]. Meanwhile, the neural elements should be retracted and protected during the operation. Therefore, the placement of a regular infusion cage of open surgery remains a technical challenge in minimally invasive endoscopic surgery using a trocar diameter usually of 20e22 mm [11e13]. Although using larger-diameter trocars or expandable retractors could somewhat improve the operating environment, the selection of a trocar-matched narrow-surface cage of suitable size may be a solution to this problem. The objective of this study was to investigate the feasibility and effectiveness of application of a narrow-surface (8-mm-wide) interbody fusion cage in full endoscopic minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) for the treatment of lumbar degenerative disease.
2. Materials and Methods 2.1. Patient data From Jun 2013 to Dec 2014, a total of 42 patients underwent full endoscopic minimally invasive transforaminal lumbar interbody fusion at our hospital was recruited. The inclusion criteria were as follows: 1) lumbar disc herniation with segmental instability or intervertebral disc space narrowing; 2) lumbar canal stenosis with intermittent claudication; 3) degenerative spondylolisthesis with low back and/or leg pain; 4) symptoms not improved after nonsurgical treatment for at least 3 months. Patients with severe osteoporosis, 3 or more segments affected, revision surgery, and bilateral lateral recesses stenosis requiring concurrent bilateral decompression were excluded. The cohort consisted of 23 males and 19 females, with a mean age of 64.2 ± 12.8 years (range: 37e75 years) (Table 1). Thirty-four of these patients were diagnosed as lumbar canal stenosis, 6 patients were diagnosed as degenerative spondylolisthesis, and 2 patients were lumbar disc herniation with segmental instability. One segment was involved in 28 patients as follows: L3-4 in 4 patients, L4-5 in 11 patients, and L5-S1 in 13 patients. Two segments were involved in 14 patients as follows: L3-4 and L4-5 in 5 patients and L4-5 and L5-S1 in 9 patients. In this series, all surgeries were performed by one senior surgeon (E.X.H.), who is proficient in minimally invasive spine surgery with more than 10 years' experience. This study was approved by the Institutional Ethic
Table 1 Clinical demographics of patients. Parameters
Values
Number of patients Mean age (y) Sex ratio (M/F) Diagnosis Lumbar canal stenosis Degenerative spondylolisthesis Lumbar disc herniation Level of fusion L3-4 L4-5 L5-S1
42 64.2 ± 12.8 (range 37e75) 23/19 34 (81.0%) 6 (14.3%) 2 (4.8%) 9 (16.1%) 25 (44.6%) 22 (39.3%)
Note: Data are presented as n (%) or mean ± standard deviation; M ¼ Male, F ¼ Female.
Committee of our hospital, and informed consents were obtained from all participants. 2.2. Surgical technique The patient was positioned prone on top of surgical pads with the abdomen free. The operative field was disinfected and draped, and the location of the targeted segmental space was marked on the skin according to preoperative fluoroscopy. First, a stab incision was made 3e4 cm away from the midline. A guide needle was then inserted into the desired location, which was determined by C-arm fluoroscopy. The incision was extended longitudinally to a length of 25 mm. A series of dilation probes ranging from small to large were inserted through the paraspinal muscle to enlarge the approach (Fig. 1A). Finally, a 22-mm working trocar was inserted and secured with the mounting system (Fig. 1B). Fluoroscopy was repeated to align the working trocar directly aiming the targeted intervertebral space on the lateral view (Fig. 1C). A electrical cautery was used to remove the remaining soft tissue on the bone surface, and a 25 rigid endoscope was then placed to identify anatomical structures under appropriate visualization (Fig. 1D). Resection of the inferior and superior facet joints, along with laminectomy and removal of ligamentum flavum were performed to accomplish canal decompression (Fig. 2A and B). If contralateral decompression was indicated, the working trocar was tilted to the medial side and further removal of the contralateral inner layer of the lamina was achieved. After removal of intervertebral disc and preparation of endplates (Fig. 2C and D), the previously resected autologous bone were mixed with allogeneic bone and grounded into bone chips, which was then packed into the intervertebral space via a specialized cannula (Fig. 3A). Finally, an 8-mm-wide narrow-surface fusion cage made of polyetheretherketone (PEEK) (Double Medical Technology Inc, Xiamen, China) was selected with different heights corresponding to the targeted intervertebral space (Fig. 3B). The cage was firmly packed with bone chips and then gently hammered toward anteromedial direction into the intervertebral space while protection of the nerves and cord was carefully noted under endoscopic monitoring (Fig. 3C). Lateral radiograph was obtained to secure the satisfactory position of the implanted fusion cage (Fig. 3D). Long-arm pedicle screws and connecting rods (Double Medical Technology Inc, Xiamen, China) were inserted percutaneously under C-arm fluoroscopic guidance. Bilateral compression was performed before final tightening of the pedicle screw-rod construct. 2.3. Clinical assessment and statistical analysis One independent observer, who was blinded to all included cases, evaluated the following parameters: operation time, intraoperative blood loss, incision length, perioperative complications, hospital stay and postoperative ambulatory time. Visual analog scale (VAS) and Oswestry disability index (ODI) scores were also recorded before surgery, 3 months after surgery, and at the last follow-up. Comparisons on clinical outcomes before and after surgery were tested by paired sample t-test. At the last follow-up, Nakai grading system [14] was applied to assess patients' satisfaction; meanwhile, interbody fusion was evaluated using computed tomography (CT) [15]. In this study, statistical analysis was performed using SPSS version 16.0 (SPSS, Chicago, IL, USA) and significance was defined as P < 0.05. 3. Results A total of 42 patients were included in this study. The mean operation time was 233.1 ± 69.5 min (range: 120e340 min). The
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Fig. 1. Photographs showing intraoperative setup of the endoscopic system. (A) A series of sequential dilators were inserted through the paraspinal muscle to enlarge the approach; (B) A 22-mm working trocar was then applied and secured with the mounting system; (C) Lateral radiograph was performed to align the working trocar directly aiming the targeted intervertebral space; (D) A 25 rigid endoscope was placed to view deep anatomical structures.
mean operation time for one segment procedure was 133.9 ± 16.1 min, whereas the mean time for two segments procedure was 241.3 ± 36.5 min. The mean blood loss during surgery was 221.8 ± 98.5 ml (range: 100e550 ml), and the mean incision length was 3.3 ± 1.2 cm (range: 2.5e5 cm). The mean hospital stay was 9.6 ± 1.3 days (range: 7e12 days), whereas the mean postoperative ambulatory time was 2.3 ± 0.3 days (range: 2e4 days). The mean volume of bone chips filled in the intervertebral space was 8.4 ± 3.7 ml (range: 6e16 ml), and the mean amount of bone chips in the fusion cage was 2.1 ± 0.3 ml (range: 1.5e2.5 ml). Two patients developed postoperative neurological complications. One patients suffered from declined muscle strength (level II) upon dorsiflexion of the toe and ankle immediately after surgery, which was considered as the result of intraoperative nerve retraction injury. At 6 months after surgery, the patient demonstrated significant improvement of the symptoms but still had a muscle strength of level IV. Another patient developed severe radiating pain to the right leg after surgery, which was subsequently confirmed as a 5-mm medial penetration of the right S1 pedicle screw. Revision surgery was performed to reposition this screw, and the symptom of the patient resolved finally. The mean follow-up period was 27.6 ± 3.8 months (range: 24e36 months). The ODI scores were 42.3 ± 5.7 before surgery, and decreased significantly 3 months after surgery (31.4 ± 13.2, P ¼ 0.024), and at the last follow-up (28.6 ± 11.1, P ¼ 0.015) (Table 2). The VAS scores were 7.2 ± 1.7, 3.1 ± 1.1, and 1.5 ± 1.2 before surgery, 3 months after surgery, and at the final follow-up, respectively (P < 0.05) (Table 2). Based on the Nakai grading system, the outcome of surgery was graded as excellent for 32 patients, good for 8 patients, and acceptable for 2 patients, corresponding to a success rate (“good” and “excellent”) of 95.2%.
Thirty-nine of the 42 patients demonstrated solid interbody fusion at the last follow-up, indicating a fusion rate of 92.9%. No screw loosening, rod breakage, or other hardware failures was found in postoperative follow-ups.
4. Discussion In 1997, Foley first carried out lumbar discectomy using a small rigid endoscope with an 18-mm working trocar. This technique was well-known as lumbar micro-endoscopic discectomy (MED) [6]. Since then, minimally invasive lumbar discectomy and decompression under endoscopy have become more and more popular in spine surgery worldwide [6e9]. However, the use of endoscopy for lumbar interbody fusion still remains a challenge in clinical practice. In 2003, Khoo et al. [11] successfully performed minimally invasive posterior lumbar interbody fusion (MIS-PLIF) with a 20mm trocar in cadavers and 3 patients preliminarily. After that, Issac et al. [4] and Yang et al. [2] have both reported minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) with a 20-mm trocar under the assistance of endoscopy. Generally, lumbar endoscopic interbody fusion is technically demanding for most spine surgeons. The diameter of the working trocar and size of the infusion cage are 2 important factors to be considered in operation. A small-diameter trocar has limited space and the endoscope may be easily obstructed by instruments. Conversely, a large-diameter trocar is convenient for surgery but increases surgical trauma to the soft tissue. Thus, a narrow-surface fusion cage may help to facilitate implantation and improve surgical safety. However, most fusion cages used in conventional open surgery are wider than 10 mm, and few studies have reported the selection of a small-size cage for endoscopic lumbar interbody
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Fig. 2. Photographs showing surgical manipulations under endoscopic monitoring. (A) Facetectomy and laminectomy were performed to remove bony compression and obtain access to the canal; (B) Ligamentum flavum was resected to clearly reveal the underlying nerve root (black arrow); (C) Slight medial retraction of the nerve root was acquired to expose the intervertebral disc (black arrow); (D) After disc resection and endplate preparation, the intervertebral space was ready for bone grafting and cage implantation (black arrow).
fusion. In the current study, we used an 8-mm-wide narrowsurface fusion cage in full endoscopic MIS-TLIF for the treatment of lumbar degenerative disease (Fig. 4AeF). All cages were placed successfully and safely under endoscopic monitoring. Only 1 patient demonstrated neurological deficit probably due to nerve root retraction during cage implantation. The fusion rate with a minimal follow-up of 2 years was as high as 92.9%. Our results indicated that the application of a narrow-surface cage in full endoscopic MIS-TLIF is a feasible and effective technique for minimally invasive spine surgery. The application of pedicle screws combined with a variety of fusion cages has been shown to achieve adequate vertebral stability [16,17]. However, different combinations may affect the stress distribution in the fixation system. A large weight-bearing surface (area of direct contact surface between the endplate and fusion cage) of a fusion cage can share the endplate stress and reduce the load of posterior pedicle screw fixation system to improve intervertebral stability. Thus, the risk of endplate collapse and the breakage of the screw or the rod is minimized. Conversely, a fusion cage with a small weight-bearing surface cannot share excessive stress on the endplate and may cause endplate collapse. This stress then directly acts on the posterior fixation system. If this stress exceeds the maximum limit, complications of the screw and rod fixation system may occur [18]. Interbody fusion with double fusion cages can increase the total weight-bearing surface, but requires bilateral approaches and the surgical trauma is also increased.
Experimental and clinical studies have demonstrated that the application of a single fusion cage combined with pedicle screw fixation stabilizes the spine in either open TLIF or PLIF surgery [19]. For open procedures, a fusion cage with an at least 10-mm-wide weight-bearing surface is commonly used if only a single fusion cage is required. Moreover, Fogel et al. [20] reported that a 9-mmwide fusion cage was the only choice in some cases due to the limited operation space. The long-term follow-up results of their study showed that the application of a single narrow-surface fusion cage can maintain the stability of vertebral segments when combined with pedicle screw fixation. Moreover, the reported endoscopic fusion procedure varies by surgeons. Khoo et al. [11] preferred using double fusion cages via bilateral approaches for the MIS-PLIF procedure. However, Isacc et al. [4] preferred using double fusion cages via a lateral approach, and Yang et al. [2] preferred using a single fusion cage. To date, no well-accepted study exists on how small weightbearing surface a fusion cage should at least have for effective lumbar interbody fusion. Considering the physical characteristics of Chinese population, we selected an 8-mm wide fusion cage with a bullet-shape head (22 or 26 mm in length). This type of fusion cage features a smaller weight-bearing surface in width than conventional cages. It is suitable for endoscopic implantation and consequently defined as narrow-surface fusion cage. Our study showed that a narrow-surface fusion cage combined with percutaneous pedicle screw fixation can sufficiently stabilize the spine, and avoid
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Fig. 3. Photographs showing interbody bone grafting and cage implantation. (A) A specialized cannula was used to pack bone chips into the intervertebral space; (B) An 8-mm-wide narrow-surface fusion cage was selected and firmly packed with bone chips; (C) The cage was then gently hammered into the intervertebral space under endoscopic monitoring with medial protection of the nerve root; (D) Lateral radiograph was obtained to secure the satisfactory position of the fusion cage.
Table 2 Comparison of ODI and VAS scores before and after surgery.
Preoperation 3 months postop Last follow-up
ODI
P
VAS
P
42.3 ± 5.7 31.4 ± 13.2 28.6 ± 11.1
e 0.024* 0.015*
7.2 ± 1.7 3.1 ± 1.1 1.5 ± 1.2
e 0.011* 0.003*
Note: * Comparing with preoperation; ODI ¼ Oswestry disability index; VAS ¼ Visual analog scale.
significant intervertebral space collapse and internal fixation failure. The amount of bone graft in the intervertebral space will positively affect the fusion of the affected segments after surgery [21,22]. Moreover, bone grafts should cover more than 30% of the endplate surface to allow appropriate stability for daily activity after surgery [23]. Filling the intervertebral space with sufficient bone grafts may also prevent the ingrowth of scar tissue, which can interfere with bone fusion. A narrow-surface fusion cage may reduce the amount of bone graft impacted in the cage, but can increase the intravertebral space outside of cage for bone grafting. Fogel et al. [20] reported that the total success rate of interbody fusion was 91.1% in patients implanted with single or double 9-mm narrow-surface fusion cages, whereas it was 96.5% in patients
implanted with wide-surface conventional cages. However, interestingly, the fusion rate was 100% in 6 patients implanted with a single narrow-surface fusion cage. We speculated that bone grafts outside of the cage were exposed in a better growing environment because they were not disturbed by the cage itself. Therefore, the intervertebral space outside of the cage should be filled as many bone grafts as possible in order to make up with the limitations of using a narrow-surface fusion cage. In this study, the volume of bone graft implanted in the intervertebral space ranged from 6 to 16 ml (with an average of 8 ml), which far exceeded the volume of bone graft in the cage (average 2 ml). The fusion rate at the last follow-up was found to be 92.9%, which was comparable to those reported in previous researches. In the current study, an 8-mm wide fusion cage was easily implanted via the 22-mm working trocar, and a 25 endoscope provided clear visualization during surgery for nerve protection. Khoo et al. [11] reported a mean operation time and blood loss of 5.4 h (324 min) and 185 ml, respectively; whereas Yang et al. [2] reported a mean operation time of 178.5 ± 17.7 min and a mean blood loss of 183.9 ± 24.2 ml. Our results showed that the mean operation time and blood loss was 233.1 ± 69.5 min and 221.8 ± 98.5 ml, respectively, which was similar to previous reports. For single segment fusion, the mean operation time was only 133.9 ± 16.1 min, and most of the patients did not require blood
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Fig. 4. A 67-year-old male suffering from low back pain for 2 years and neurological intermittent claudication for 6 months. (A and B) Preoperative MR images showing pathological lumbar canal stenosis at L4/5 level; (C) Postoperative axial CT scan showing decompression of the spinal canal and implantation of a narrow-surface cage; (D and E) Postoperative anteroposterior and lateral radiographs showing excellent internal fixation; (F) Twenty-six months postoperation, sagittal reconstruction of CT scan showing the formation of trabecular bony bridges between adjacent vertebral endplates, indicating fusion.
transfusion during or after surgery. The patients quickly recovered and usually began ambulation 3 days after surgery, with significant relief of the symptoms. At 3 months postoperation and last followup, the improvements in ODI and VAS scores were statistically significant. Moreover, 95.2% of the surgeries were rated as “excellent” or “good” based on the Nakai grading system. The clinical outcome of using a narrow-surface (8-mm wide) cage in full endoscopic MIS-TLIF for treatment of lumbar degenerative disease was satisfactory and promising. Some limitations of our study should be acknowledged. First, the data were collected from one senior spine surgeon who had more than 10 years' experience of endoscopic surgery. Universal involvement of spine fellows and residents in current clinical practice may limits the comparison to our results. Second, our study lacks control group of conventional wide-surface fusion cages, because full endoscopic lumbar interbody fusion has now become a routine procedure in our center and few cases of open surgery with comparable demographics and diagnoses were encountered. Multicenter prospective studies may be conducted in a likely fashion to address this issue. 5. Conclusion Application of a narrow-surface fusion cage in full endoscopic MIS-TLIF for the treatment of lumbar degenerative disease is feasible and effective. This procedure bears several advantages,
including minimal trauma to paraspinal muscle, improved intraoperative visualization, low risk of nerve damage, and sufficient volume of bone grafts in intervertebral space. The clinical outcome and fusion success of using a narrow-surface interbody cage in full endoscopic MIS-TLIF were acceptable and promising. Ethical approval This study was approved by the Institutional Ethic Committee of The First Affiliated Hospital of Guangzhou Medical University (N2013035). Sources of funding This work was supported by Collaborative Innovation Project of The First Affiliated Hospital of Guangzhou Medical University (201506-gyfyy). Author contribution Er-xing HE: Study design, writing. Jing GUO: Data collection, writing. Qin-jie LING: Study design, data analysis. Zhi-xun YIN: Data analysis. Ying WANG: Data collection. Ming LI: Data collection.
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Conflicts of interest No conflict of interest exits in this manuscript. Guarantor Er-xing HE. Acknowledgements This work was supported by Collaborative Innovation Project of The First Affiliated Hospital of Guangzhou Medical University (201506-gyfyy). References [1] Y.T. Wang, X.T. Wu, H. Chen, C. Wang, Endoscopy-assisted posterior lumbar interbody fusion in a single segment, J. Clin. Neurosci. 21 (2014) 287e292. [2] Y. Yang, B. Liu, L.M. Rong, R.Q. Chen, J.W. Dong, P.G. Xie, L.M. Zhang, F. Feng, Microendoscopy-assisted minimally invasive transforaminal lumbar interbody fusion for lumbar degenerative disease: short-term and medium-term outcomes, Int. J. Clin. Exp. Med. 8 (2015) 21319e21326. [3] B.S. Xu, Y. Liu, H.W. Xu, Q. Yang, X.L. Ma, Y.C. Hu, Intervertebral fusion with Mobile Microendoscopic discectomy for lumbar degenerative disc disease, Orthop. Surg. 8 (2016) 241e245. [4] R.E. Isaacs, V.K. Podichetty, P. Santiago, F.A. Sandhu, J. Spears, K. Kelly, L. Rice, R.G. Fessler, Minimally invasive microendoscopy-assisted transforaminal lumbar interbody fusion with instrumentation, J. Neurosurg. Spine 3 (2005) 98e105. [5] N. Yao, W. Wang, Y. Liu, Percutaneous endoscopic lumbar discectomy and interbody fusion with B-Twin expandable spinal spacer, Arch. Orthop. Trauma Surg. 131 (2011) 791e796. [6] M.M. Smith, K.T. Foley, Microendoscopic discectomy: surgical technique and initial clinical results, Clin. Neurol. Neurosurg. 99 (1997), 105e105(101). [7] M.J. Perezcruet, K.T. Foley, R.E. Isaacs, L. Ricewyllie, R. Wellington, M.M. Smith, R.G. Fessler, Microendoscopic lumbar discectomy: technical note, Neurosurgery 51 (2002) 129e136. [8] L.T. Khoo, R.G. Fessler, Microendoscopic decompressive laminotomy for the treatment of lumbar stenosis, Neurosurgery 51 (2002) S146. [9] V. Popov, D.G. Anderson, Minimal invasive decompression for lumbar spinal
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stenosis, Adv. Orthop. 2012 (2012) 645321. [10] F. Jacquot, D. Gastambide, Percutaneous endoscopic transforaminal lumbar interbody fusion: is it worth it? Int. Orthop. 37 (2013) 1507e1510. [11] L.T. Khoo, S. Palmer, D.T. Laich, R.G. Fessler, Minimally invasive percutaneous posterior lumbar interbody fusion, Neurosurgery 52 (2003) 1512. [12] J.D. Schwender, L.T. Holly, D.P. Rouben, K.T. Foley, Minimally invasive transforaminal lumbar interbody fusion (TLIF): technical feasibility and initial results, J. Spinal Disord. Tech. 18 (Suppl) (2005) S1eS6. [13] B.M. Ozgur, K. Yoo, G. Rodriguez, W.R. Taylor, Minimally-invasive technique for transforaminal lumbar interbody fusion (TLIF), Eur. Spine J. 14 (2005) 887e894. [14] O. Nakai, A. Ookawa, I. Yamaura, Long-term roentgenographic and functional changes in patients who were treated with wide fenestration for central lumbar stenosis, J. Bone Jt. Surg. Am. 73 (1991) 1184e1191. [15] R.R. Shah, S. Mohammed, A. Saifuddin, B.A. Taylor, Comparison of plain radiographs with CT scan to evaluate interbody fusion following the use of titanium interbody cages and transpedicular instrumentation, Eur. Spine J. 12 (2003) 378e385. [16] W. Cho, C. Wu, A.A. Mehbod, E.E. Transfeldt, Comparison of cage designs for transforaminal lumbar interbody fusion: a biomechanical study, Clin. Biomech. 23 (2008) 979e985. [17] P.P. Tsitsopoulos, H. Serhan, L.I. Voronov, G. Carandang, R.M. Havey, A.J. Ghanayem, A.G. Patwardhan, Would an anatomically shaped lumbar interbody cage provide better stability? An in vitro cadaveric biomechanical evaluation, J. Spinal Disord. Tech. 25 (2012) 240e244. [18] J.S. Tan, C.S. Bailey, M.F. Dvorak, C.G. Fisher, T.R. Oxland, Interbody device shape and size are important to strengthen the vertebra-implant interface, Spine 30 (2005) 638. [19] C.P. Ames, F.L. Acosta Jr., J. Chi, J. Iyengar, W. Muiru, E. Acaroglu, C.M. Puttlitz, Biomechanical comparison of posterior lumbar interbody fusion and transforaminal lumbar interbody fusion performed at 1 and 2 levels, Spine 30 (2005) E562eE566. [20] G.R. Fogel, J.S. Toohey, A. Neidre, J.W. Brantigan, Outcomes of posterior lumbar interbody fusion with the 9-mm width lumbar I/F cage and the variable screw placement system, J. Surg. Orthop. Adv. 18 (2009) 77e82. [21] K.Y. Ha, J.S. Lee, K.W. Kim, Bone graft volumetric changes and clinical outcomes after instrumented lumbar or lumbosacral fusion: a prospective cohort study with a five-year follow-up, Spine 34 (2009) 1663. [22] P.M. Lin, Posterior lumbar interbody fusion technique: complications and pitfalls, Clin. Orthop. Relat. Res. 193 (1985) 90e102. [23] R.F. Closkey, J.R. Parsons, C.K. Lee, M.F. Blacksin, M.C. Zimmerman, Mechanics of interbody spinal fusion. Analysis of critical bone graft area, Spine 18 (1993) 1011e1015.
Contents lists available at ScienceDirect
International Journal of Surgery journal homepage: www.journal-surgery.net
Original Research
Application of a narrow-surface cage in full endoscopic minimally invasive transforaminal lumbar interbody fusion Er-xing He, M.D. a, b, *, 1, Jing Guo a, b, 1, Qin-jie Ling a, b, Zhi-xun Yin a, b, Ying Wang a, b, Ming Li a, b a b
Spine Surgery, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, China Guangzhou Orthopaedic Institute, Guangzhou, China
h i g h l i g h t s Endoscopic lumbar interbody fusion still remains a technical challenge. An 8-mm-wide narrow-surface cage was selected for 42 cases underwent endoscopic lumbar interbody fusion. All procedures were performed safely and successfully with minimal trauma and improved visualization. Clinical outcome and fusion rate of narrow-surface cage were acceptable and promising.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 March 2017 Accepted 14 April 2017 Available online 27 April 2017
Background: Spinal endoscopy has been widely applied in lumbar discectomy and decompression. However, endoscopic lumbar interbody fusion still remains a technical challenge due to the limited space within the working trocar for cage implantation. The purpose of this study was to investigate the feasibility and effectiveness of using a narrow-surface fusion cage in full endoscopic minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) for the treatment of lumbar degenerative disease. Materials and Methods: From Jun 2013 to Dec 2014, a total of 42 patients (23 males, 19 females) underwent full endoscopic MIS-TLIF at our hospital was recruited. An 8-mm-wide narrow-surface fusion cage was selected for all cases. Perioperative parameters and complications were recorded. Comparisons on visual analog scale (VAS) and oswestry disability index (ODI) scores before and after surgery were performed. At the last follow-up, Nakai grading system was applied to assess patients' satisfaction; meanwhile, interbody fusion was evaluated by computed tomography. Results: Mean operation time was 233.1 ± 69.5 min, and mean blood loss during surgery was 221.8 ± 98.5 ml. Two patients (4.8%) developed neurological complications. Postoperative follow-up ranged from 24 to 36 months (mean 27.6 ± 3.8 months). VAS and ODI scores were significantly improved 3 months after surgery and at the final follow-up, respectively (P < 0.05). Outcome of surgery was graded as excellent for 32 patients, good for 8 patients, and acceptable for 2 patients, corresponding to a success rate (“good” and “excellent”) of 95.2%. Thirty-nine of the 42 patients demonstrated solid interbody fusion at the last follow-up, indicating a fusion rate of 92.9%. Conclusion: Application of a narrow-surface fusion cage in full endoscopic MIS-TLIF for the treatment of lumbar degenerative disease is feasible and effective. The clinical outcome and fusion success of this procedure were acceptable and promising. © 2017 IJS Publishing Group Ltd. Published by Elsevier Ltd. All rights reserved.
Keywords: Minimally invasive spine surgery Endoscopy Lumbar interbody fusion Fusion cage
1. Introduction
* Corresponding author. Spine Surgery, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, China. E-mail address: [email protected] (E.-x. He). 1 The first two authors contributed equally to this work.
Current endoscopic techniques in spine surgery use varied minimally invasive working trocars to establish the surgical approach, which cause much less trauma to the paraspinal muscle compared with open surgery [1e3]. The endoscope can clearly
http://dx.doi.org/10.1016/j.ijsu.2017.04.053 1743-9191/© 2017 IJS Publishing Group Ltd. Published by Elsevier Ltd. All rights reserved.
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show the fine structures in the deep surgical field and provide excellent visualization [4,5]. Spinal endoscopy has been widely applied in lumbar discectomy and decompression [6e9]. However, reports on endoscopic lumbar interbody fusion are still in paucity. Endoscopic spine surgery differs from open surgery due to the limited space and consequently, requires specialized skills and instruments, especially for fusion cage implantation [5,10]. Meanwhile, the neural elements should be retracted and protected during the operation. Therefore, the placement of a regular infusion cage of open surgery remains a technical challenge in minimally invasive endoscopic surgery using a trocar diameter usually of 20e22 mm [11e13]. Although using larger-diameter trocars or expandable retractors could somewhat improve the operating environment, the selection of a trocar-matched narrow-surface cage of suitable size may be a solution to this problem. The objective of this study was to investigate the feasibility and effectiveness of application of a narrow-surface (8-mm-wide) interbody fusion cage in full endoscopic minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) for the treatment of lumbar degenerative disease.
2. Materials and Methods 2.1. Patient data From Jun 2013 to Dec 2014, a total of 42 patients underwent full endoscopic minimally invasive transforaminal lumbar interbody fusion at our hospital was recruited. The inclusion criteria were as follows: 1) lumbar disc herniation with segmental instability or intervertebral disc space narrowing; 2) lumbar canal stenosis with intermittent claudication; 3) degenerative spondylolisthesis with low back and/or leg pain; 4) symptoms not improved after nonsurgical treatment for at least 3 months. Patients with severe osteoporosis, 3 or more segments affected, revision surgery, and bilateral lateral recesses stenosis requiring concurrent bilateral decompression were excluded. The cohort consisted of 23 males and 19 females, with a mean age of 64.2 ± 12.8 years (range: 37e75 years) (Table 1). Thirty-four of these patients were diagnosed as lumbar canal stenosis, 6 patients were diagnosed as degenerative spondylolisthesis, and 2 patients were lumbar disc herniation with segmental instability. One segment was involved in 28 patients as follows: L3-4 in 4 patients, L4-5 in 11 patients, and L5-S1 in 13 patients. Two segments were involved in 14 patients as follows: L3-4 and L4-5 in 5 patients and L4-5 and L5-S1 in 9 patients. In this series, all surgeries were performed by one senior surgeon (E.X.H.), who is proficient in minimally invasive spine surgery with more than 10 years' experience. This study was approved by the Institutional Ethic
Table 1 Clinical demographics of patients. Parameters
Values
Number of patients Mean age (y) Sex ratio (M/F) Diagnosis Lumbar canal stenosis Degenerative spondylolisthesis Lumbar disc herniation Level of fusion L3-4 L4-5 L5-S1
42 64.2 ± 12.8 (range 37e75) 23/19 34 (81.0%) 6 (14.3%) 2 (4.8%) 9 (16.1%) 25 (44.6%) 22 (39.3%)
Note: Data are presented as n (%) or mean ± standard deviation; M ¼ Male, F ¼ Female.
Committee of our hospital, and informed consents were obtained from all participants. 2.2. Surgical technique The patient was positioned prone on top of surgical pads with the abdomen free. The operative field was disinfected and draped, and the location of the targeted segmental space was marked on the skin according to preoperative fluoroscopy. First, a stab incision was made 3e4 cm away from the midline. A guide needle was then inserted into the desired location, which was determined by C-arm fluoroscopy. The incision was extended longitudinally to a length of 25 mm. A series of dilation probes ranging from small to large were inserted through the paraspinal muscle to enlarge the approach (Fig. 1A). Finally, a 22-mm working trocar was inserted and secured with the mounting system (Fig. 1B). Fluoroscopy was repeated to align the working trocar directly aiming the targeted intervertebral space on the lateral view (Fig. 1C). A electrical cautery was used to remove the remaining soft tissue on the bone surface, and a 25 rigid endoscope was then placed to identify anatomical structures under appropriate visualization (Fig. 1D). Resection of the inferior and superior facet joints, along with laminectomy and removal of ligamentum flavum were performed to accomplish canal decompression (Fig. 2A and B). If contralateral decompression was indicated, the working trocar was tilted to the medial side and further removal of the contralateral inner layer of the lamina was achieved. After removal of intervertebral disc and preparation of endplates (Fig. 2C and D), the previously resected autologous bone were mixed with allogeneic bone and grounded into bone chips, which was then packed into the intervertebral space via a specialized cannula (Fig. 3A). Finally, an 8-mm-wide narrow-surface fusion cage made of polyetheretherketone (PEEK) (Double Medical Technology Inc, Xiamen, China) was selected with different heights corresponding to the targeted intervertebral space (Fig. 3B). The cage was firmly packed with bone chips and then gently hammered toward anteromedial direction into the intervertebral space while protection of the nerves and cord was carefully noted under endoscopic monitoring (Fig. 3C). Lateral radiograph was obtained to secure the satisfactory position of the implanted fusion cage (Fig. 3D). Long-arm pedicle screws and connecting rods (Double Medical Technology Inc, Xiamen, China) were inserted percutaneously under C-arm fluoroscopic guidance. Bilateral compression was performed before final tightening of the pedicle screw-rod construct. 2.3. Clinical assessment and statistical analysis One independent observer, who was blinded to all included cases, evaluated the following parameters: operation time, intraoperative blood loss, incision length, perioperative complications, hospital stay and postoperative ambulatory time. Visual analog scale (VAS) and Oswestry disability index (ODI) scores were also recorded before surgery, 3 months after surgery, and at the last follow-up. Comparisons on clinical outcomes before and after surgery were tested by paired sample t-test. At the last follow-up, Nakai grading system [14] was applied to assess patients' satisfaction; meanwhile, interbody fusion was evaluated using computed tomography (CT) [15]. In this study, statistical analysis was performed using SPSS version 16.0 (SPSS, Chicago, IL, USA) and significance was defined as P < 0.05. 3. Results A total of 42 patients were included in this study. The mean operation time was 233.1 ± 69.5 min (range: 120e340 min). The
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Fig. 1. Photographs showing intraoperative setup of the endoscopic system. (A) A series of sequential dilators were inserted through the paraspinal muscle to enlarge the approach; (B) A 22-mm working trocar was then applied and secured with the mounting system; (C) Lateral radiograph was performed to align the working trocar directly aiming the targeted intervertebral space; (D) A 25 rigid endoscope was placed to view deep anatomical structures.
mean operation time for one segment procedure was 133.9 ± 16.1 min, whereas the mean time for two segments procedure was 241.3 ± 36.5 min. The mean blood loss during surgery was 221.8 ± 98.5 ml (range: 100e550 ml), and the mean incision length was 3.3 ± 1.2 cm (range: 2.5e5 cm). The mean hospital stay was 9.6 ± 1.3 days (range: 7e12 days), whereas the mean postoperative ambulatory time was 2.3 ± 0.3 days (range: 2e4 days). The mean volume of bone chips filled in the intervertebral space was 8.4 ± 3.7 ml (range: 6e16 ml), and the mean amount of bone chips in the fusion cage was 2.1 ± 0.3 ml (range: 1.5e2.5 ml). Two patients developed postoperative neurological complications. One patients suffered from declined muscle strength (level II) upon dorsiflexion of the toe and ankle immediately after surgery, which was considered as the result of intraoperative nerve retraction injury. At 6 months after surgery, the patient demonstrated significant improvement of the symptoms but still had a muscle strength of level IV. Another patient developed severe radiating pain to the right leg after surgery, which was subsequently confirmed as a 5-mm medial penetration of the right S1 pedicle screw. Revision surgery was performed to reposition this screw, and the symptom of the patient resolved finally. The mean follow-up period was 27.6 ± 3.8 months (range: 24e36 months). The ODI scores were 42.3 ± 5.7 before surgery, and decreased significantly 3 months after surgery (31.4 ± 13.2, P ¼ 0.024), and at the last follow-up (28.6 ± 11.1, P ¼ 0.015) (Table 2). The VAS scores were 7.2 ± 1.7, 3.1 ± 1.1, and 1.5 ± 1.2 before surgery, 3 months after surgery, and at the final follow-up, respectively (P < 0.05) (Table 2). Based on the Nakai grading system, the outcome of surgery was graded as excellent for 32 patients, good for 8 patients, and acceptable for 2 patients, corresponding to a success rate (“good” and “excellent”) of 95.2%.
Thirty-nine of the 42 patients demonstrated solid interbody fusion at the last follow-up, indicating a fusion rate of 92.9%. No screw loosening, rod breakage, or other hardware failures was found in postoperative follow-ups.
4. Discussion In 1997, Foley first carried out lumbar discectomy using a small rigid endoscope with an 18-mm working trocar. This technique was well-known as lumbar micro-endoscopic discectomy (MED) [6]. Since then, minimally invasive lumbar discectomy and decompression under endoscopy have become more and more popular in spine surgery worldwide [6e9]. However, the use of endoscopy for lumbar interbody fusion still remains a challenge in clinical practice. In 2003, Khoo et al. [11] successfully performed minimally invasive posterior lumbar interbody fusion (MIS-PLIF) with a 20mm trocar in cadavers and 3 patients preliminarily. After that, Issac et al. [4] and Yang et al. [2] have both reported minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) with a 20-mm trocar under the assistance of endoscopy. Generally, lumbar endoscopic interbody fusion is technically demanding for most spine surgeons. The diameter of the working trocar and size of the infusion cage are 2 important factors to be considered in operation. A small-diameter trocar has limited space and the endoscope may be easily obstructed by instruments. Conversely, a large-diameter trocar is convenient for surgery but increases surgical trauma to the soft tissue. Thus, a narrow-surface fusion cage may help to facilitate implantation and improve surgical safety. However, most fusion cages used in conventional open surgery are wider than 10 mm, and few studies have reported the selection of a small-size cage for endoscopic lumbar interbody
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Fig. 2. Photographs showing surgical manipulations under endoscopic monitoring. (A) Facetectomy and laminectomy were performed to remove bony compression and obtain access to the canal; (B) Ligamentum flavum was resected to clearly reveal the underlying nerve root (black arrow); (C) Slight medial retraction of the nerve root was acquired to expose the intervertebral disc (black arrow); (D) After disc resection and endplate preparation, the intervertebral space was ready for bone grafting and cage implantation (black arrow).
fusion. In the current study, we used an 8-mm-wide narrowsurface fusion cage in full endoscopic MIS-TLIF for the treatment of lumbar degenerative disease (Fig. 4AeF). All cages were placed successfully and safely under endoscopic monitoring. Only 1 patient demonstrated neurological deficit probably due to nerve root retraction during cage implantation. The fusion rate with a minimal follow-up of 2 years was as high as 92.9%. Our results indicated that the application of a narrow-surface cage in full endoscopic MIS-TLIF is a feasible and effective technique for minimally invasive spine surgery. The application of pedicle screws combined with a variety of fusion cages has been shown to achieve adequate vertebral stability [16,17]. However, different combinations may affect the stress distribution in the fixation system. A large weight-bearing surface (area of direct contact surface between the endplate and fusion cage) of a fusion cage can share the endplate stress and reduce the load of posterior pedicle screw fixation system to improve intervertebral stability. Thus, the risk of endplate collapse and the breakage of the screw or the rod is minimized. Conversely, a fusion cage with a small weight-bearing surface cannot share excessive stress on the endplate and may cause endplate collapse. This stress then directly acts on the posterior fixation system. If this stress exceeds the maximum limit, complications of the screw and rod fixation system may occur [18]. Interbody fusion with double fusion cages can increase the total weight-bearing surface, but requires bilateral approaches and the surgical trauma is also increased.
Experimental and clinical studies have demonstrated that the application of a single fusion cage combined with pedicle screw fixation stabilizes the spine in either open TLIF or PLIF surgery [19]. For open procedures, a fusion cage with an at least 10-mm-wide weight-bearing surface is commonly used if only a single fusion cage is required. Moreover, Fogel et al. [20] reported that a 9-mmwide fusion cage was the only choice in some cases due to the limited operation space. The long-term follow-up results of their study showed that the application of a single narrow-surface fusion cage can maintain the stability of vertebral segments when combined with pedicle screw fixation. Moreover, the reported endoscopic fusion procedure varies by surgeons. Khoo et al. [11] preferred using double fusion cages via bilateral approaches for the MIS-PLIF procedure. However, Isacc et al. [4] preferred using double fusion cages via a lateral approach, and Yang et al. [2] preferred using a single fusion cage. To date, no well-accepted study exists on how small weightbearing surface a fusion cage should at least have for effective lumbar interbody fusion. Considering the physical characteristics of Chinese population, we selected an 8-mm wide fusion cage with a bullet-shape head (22 or 26 mm in length). This type of fusion cage features a smaller weight-bearing surface in width than conventional cages. It is suitable for endoscopic implantation and consequently defined as narrow-surface fusion cage. Our study showed that a narrow-surface fusion cage combined with percutaneous pedicle screw fixation can sufficiently stabilize the spine, and avoid
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Fig. 3. Photographs showing interbody bone grafting and cage implantation. (A) A specialized cannula was used to pack bone chips into the intervertebral space; (B) An 8-mm-wide narrow-surface fusion cage was selected and firmly packed with bone chips; (C) The cage was then gently hammered into the intervertebral space under endoscopic monitoring with medial protection of the nerve root; (D) Lateral radiograph was obtained to secure the satisfactory position of the fusion cage.
Table 2 Comparison of ODI and VAS scores before and after surgery.
Preoperation 3 months postop Last follow-up
ODI
P
VAS
P
42.3 ± 5.7 31.4 ± 13.2 28.6 ± 11.1
e 0.024* 0.015*
7.2 ± 1.7 3.1 ± 1.1 1.5 ± 1.2
e 0.011* 0.003*
Note: * Comparing with preoperation; ODI ¼ Oswestry disability index; VAS ¼ Visual analog scale.
significant intervertebral space collapse and internal fixation failure. The amount of bone graft in the intervertebral space will positively affect the fusion of the affected segments after surgery [21,22]. Moreover, bone grafts should cover more than 30% of the endplate surface to allow appropriate stability for daily activity after surgery [23]. Filling the intervertebral space with sufficient bone grafts may also prevent the ingrowth of scar tissue, which can interfere with bone fusion. A narrow-surface fusion cage may reduce the amount of bone graft impacted in the cage, but can increase the intravertebral space outside of cage for bone grafting. Fogel et al. [20] reported that the total success rate of interbody fusion was 91.1% in patients implanted with single or double 9-mm narrow-surface fusion cages, whereas it was 96.5% in patients
implanted with wide-surface conventional cages. However, interestingly, the fusion rate was 100% in 6 patients implanted with a single narrow-surface fusion cage. We speculated that bone grafts outside of the cage were exposed in a better growing environment because they were not disturbed by the cage itself. Therefore, the intervertebral space outside of the cage should be filled as many bone grafts as possible in order to make up with the limitations of using a narrow-surface fusion cage. In this study, the volume of bone graft implanted in the intervertebral space ranged from 6 to 16 ml (with an average of 8 ml), which far exceeded the volume of bone graft in the cage (average 2 ml). The fusion rate at the last follow-up was found to be 92.9%, which was comparable to those reported in previous researches. In the current study, an 8-mm wide fusion cage was easily implanted via the 22-mm working trocar, and a 25 endoscope provided clear visualization during surgery for nerve protection. Khoo et al. [11] reported a mean operation time and blood loss of 5.4 h (324 min) and 185 ml, respectively; whereas Yang et al. [2] reported a mean operation time of 178.5 ± 17.7 min and a mean blood loss of 183.9 ± 24.2 ml. Our results showed that the mean operation time and blood loss was 233.1 ± 69.5 min and 221.8 ± 98.5 ml, respectively, which was similar to previous reports. For single segment fusion, the mean operation time was only 133.9 ± 16.1 min, and most of the patients did not require blood
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Fig. 4. A 67-year-old male suffering from low back pain for 2 years and neurological intermittent claudication for 6 months. (A and B) Preoperative MR images showing pathological lumbar canal stenosis at L4/5 level; (C) Postoperative axial CT scan showing decompression of the spinal canal and implantation of a narrow-surface cage; (D and E) Postoperative anteroposterior and lateral radiographs showing excellent internal fixation; (F) Twenty-six months postoperation, sagittal reconstruction of CT scan showing the formation of trabecular bony bridges between adjacent vertebral endplates, indicating fusion.
transfusion during or after surgery. The patients quickly recovered and usually began ambulation 3 days after surgery, with significant relief of the symptoms. At 3 months postoperation and last followup, the improvements in ODI and VAS scores were statistically significant. Moreover, 95.2% of the surgeries were rated as “excellent” or “good” based on the Nakai grading system. The clinical outcome of using a narrow-surface (8-mm wide) cage in full endoscopic MIS-TLIF for treatment of lumbar degenerative disease was satisfactory and promising. Some limitations of our study should be acknowledged. First, the data were collected from one senior spine surgeon who had more than 10 years' experience of endoscopic surgery. Universal involvement of spine fellows and residents in current clinical practice may limits the comparison to our results. Second, our study lacks control group of conventional wide-surface fusion cages, because full endoscopic lumbar interbody fusion has now become a routine procedure in our center and few cases of open surgery with comparable demographics and diagnoses were encountered. Multicenter prospective studies may be conducted in a likely fashion to address this issue. 5. Conclusion Application of a narrow-surface fusion cage in full endoscopic MIS-TLIF for the treatment of lumbar degenerative disease is feasible and effective. This procedure bears several advantages,
including minimal trauma to paraspinal muscle, improved intraoperative visualization, low risk of nerve damage, and sufficient volume of bone grafts in intervertebral space. The clinical outcome and fusion success of using a narrow-surface interbody cage in full endoscopic MIS-TLIF were acceptable and promising. Ethical approval This study was approved by the Institutional Ethic Committee of The First Affiliated Hospital of Guangzhou Medical University (N2013035). Sources of funding This work was supported by Collaborative Innovation Project of The First Affiliated Hospital of Guangzhou Medical University (201506-gyfyy). Author contribution Er-xing HE: Study design, writing. Jing GUO: Data collection, writing. Qin-jie LING: Study design, data analysis. Zhi-xun YIN: Data analysis. Ying WANG: Data collection. Ming LI: Data collection.
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Conflicts of interest No conflict of interest exits in this manuscript. Guarantor Er-xing HE. Acknowledgements This work was supported by Collaborative Innovation Project of The First Affiliated Hospital of Guangzhou Medical University (201506-gyfyy). References [1] Y.T. Wang, X.T. Wu, H. Chen, C. Wang, Endoscopy-assisted posterior lumbar interbody fusion in a single segment, J. Clin. Neurosci. 21 (2014) 287e292. [2] Y. Yang, B. Liu, L.M. Rong, R.Q. Chen, J.W. Dong, P.G. Xie, L.M. Zhang, F. Feng, Microendoscopy-assisted minimally invasive transforaminal lumbar interbody fusion for lumbar degenerative disease: short-term and medium-term outcomes, Int. J. Clin. Exp. Med. 8 (2015) 21319e21326. [3] B.S. Xu, Y. Liu, H.W. Xu, Q. Yang, X.L. Ma, Y.C. Hu, Intervertebral fusion with Mobile Microendoscopic discectomy for lumbar degenerative disc disease, Orthop. Surg. 8 (2016) 241e245. [4] R.E. Isaacs, V.K. Podichetty, P. Santiago, F.A. Sandhu, J. Spears, K. Kelly, L. Rice, R.G. Fessler, Minimally invasive microendoscopy-assisted transforaminal lumbar interbody fusion with instrumentation, J. Neurosurg. Spine 3 (2005) 98e105. [5] N. Yao, W. Wang, Y. Liu, Percutaneous endoscopic lumbar discectomy and interbody fusion with B-Twin expandable spinal spacer, Arch. Orthop. Trauma Surg. 131 (2011) 791e796. [6] M.M. Smith, K.T. Foley, Microendoscopic discectomy: surgical technique and initial clinical results, Clin. Neurol. Neurosurg. 99 (1997), 105e105(101). [7] M.J. Perezcruet, K.T. Foley, R.E. Isaacs, L. Ricewyllie, R. Wellington, M.M. Smith, R.G. Fessler, Microendoscopic lumbar discectomy: technical note, Neurosurgery 51 (2002) 129e136. [8] L.T. Khoo, R.G. Fessler, Microendoscopic decompressive laminotomy for the treatment of lumbar stenosis, Neurosurgery 51 (2002) S146. [9] V. Popov, D.G. Anderson, Minimal invasive decompression for lumbar spinal
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