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Clinical Effect of Minimally Invasive Microendoscopic‐Assisted Transforaminal Lumbar Interbody Fusion for Single‐Level Lumbar Disc Herniation

Objective This retrospective study aimed to compare the clinical and radiological outcomes of transforaminal lumbar interbody fusion (TLIF) through the Wiltse approach (W‐TLIF) vs minimally invasive microendoscopy‐assisted transforaminal lumbar interbody fusion (ME‐TLIF) in single‐segment lumbar disc herniation (LDH). Methods A retrospective study was conducted to study the differences in specific clinical outcomes between single‐segment LDH patients receiving W‐TLIF and ME‐TLIF. Single‐segment LDH patients admitted to the Fujian Medical University Union Hospital from March 2015 to June 2018 were included. All the participants were divided into the ME‐TLIF group or the W‐TLIF group according to their TLIF surgery types. Demographic characteristics, the visual analog score (VAS), Oswestry Disability Index (ODI), Japanese Orthopaedic Association (JOA) scale, blood loss volume, postoperative drainage, ambulated time, initial postoperative back pain, hospitalization duration, expenses, and improvement rates of patients in the two groups were collected for analysis. Radiographic fusion was ultimately assessed via the Bridwell interbody fusion grading system. All selected patients with TLIF were followed up for 1 year. Results Fifty‐seven patients were selected, with 26 in the ME‐TLIF group and 31 in the W‐TLIF group, both of whom were followed up for 1 year. The mean age of the included patients was 53.75 ± 9.313 years, and the sex ratio was indiscrimination. There was no significant difference in demographic data or operating time between the two groups prior to surgery. The blood loss volume (ME‐TLIF: 228.5 vs W‐TLIF: 681.3), postoperative drainage (ME‐TLIF:82.1 ± 23.5 vs W‐TLIF: 345.8 ± 65.2), initial postoperative back pain (ME‐TLIF: VAS_3 days: 1.96 ± 0.60 VAS_7 days: 1.73 ± 0.53, W‐TLIF: VAS_3 days: 2.48 ± 0.51 VAS_7 days: 1.87 ± 0.43), and hospitalization duration (ME‐TLIF: 9.04 vs. W‐TLIF: 11.29) were all significantly lower in the ME‐TILF group (p < 0.05). However, there were no statistical differences between the two groups in VAS, ODI, and JOA at 1 month, 3 months, 6 months, and 1 year postoperatively (p > 0.05). The fusion rates of the two groups showed no notable difference (p > 0.05), while the X‐ray exposure time in the ME‐TLIF group was significantly longer than in the W‐TLIF group (p < 0.05). Conclusions ME‐TLIF surgery was an effective and satisfactory surgical technique to manage LDH. Although ME‐TLIF increased the operation time and intraoperative fluoroscopic irradiation volume, it could effectively relieve low back pain from early postoperative onset and promote early postoperative recovery compared with W‐TLIF.


Introduction
L umbar disc herniation (LDH) with lumbar instability is a common cause of low back pain, radiculopathy, and/or neurogenic claudication. 1,2 Patients with LDH prefer to choose surgical decompression of the neural elements and stabilize spinal fusion after invalid non-operative treatment. 3,4 Currently, transforaminal lumbar interbody fusion (TLIF) and posterior lumbar interbody fusion (PLIF) are two widely used types of surgery for LDH therapy. [5][6][7] The indications for lumbar interbody fusion mainly include: low back pain, lumbar disc herniation, neurogenic claudication, radiculopathy due to foraminal stenosis, spinal instability, and lumbar degenerative spinal deformity that includes symptomatic spondylolisthesis, and degenerative scoliosis. [8][9][10] The carragee grading as shown in Figure 1 is helpful in understanding disc herniation and nerve root compression. Cloward firstly proposed PLIF surgery in the 1940s, 11 but Styf and Willén revealed that PLIF surgery would dissect intraoperative paravertebral muscles in a wide range and lead to dural tear, nerve injury, or epidural scarring due to decompression and fixation. 12 To reduce paraspinal muscle injury and promote postoperative recovery, Harms and Rollinger introduced transforaminal lumbar interbody fusion (TLIF) surgery in 1982, 13 which has become a popular and well-established technique. TLIF surgery enters along the intermuscular space of the multifidus and longus muscles into low back, and it requires extensive intraoperative dissection and retraction of the paraspinal muscular ligamentous unit, [14][15][16] which can result in local muscle necrosis, fibers scaring, and increased incidence of low back pain (LBP). [17][18][19] The minimally invasive spine surgery innovation and advanced devices promote the minimally invasive TLIF in LDH. 20,21 Thus, Foley et al. first proposed minimally invasive TLIF aiming to reduce and avoid intraoperative multifidus stripping and stretching. 22 While ME-TLIF induces less damage to paravertebral muscles and has better postoperative outcomes compared with conventional TLIF, several studies reported several limitations of ME-TLIF, including incomplete decompression and longer radiation exposure and operation time. 16,23,24 In 2005, Isaacs 25 pioneered the use of endoscopic discectomy and interbody fusion techniques with intraoperative blunt distension that could better protect the multifidus muscle, paraspinal muscles, and surrounding soft tissue from injury.
However, limited studies have focused on the differences in clinical effects between ME-TLIF and W-TLIF in treating patients with single-stage LDH. Since 2015, our institution has performed ME-TLIF surgery with microendoscopic assistance for LDH. This technique can provide adequate light, 10 times the maximum vision field, and clearer surgical vision field. The tubular working channel can be angled directly to facilitate direct decompression of other areas, such as the contralateral nerve root canal. 26 Furthermore, ME-TLIF surgery has a varied range of surgery applications, including lumbar spinal stenosis, lumbar disc herniation, degenerative lumbar spondylolisthesis. 16,27 Therefore, this study aimed to: (1) compare the perioperative data, clinical results, and imaging findings of ME-TLIF and W-TLIF in the treatment of single-stage LDH; (2) determine the advantages of ME-TLIF surgical method and understand the shortcomings of this method; (3) provide clinical case support for the application of the ME-TLIF surgical method. the participants were diagnosed with single-segment LDH based on image examination. All data were collected postoperatively from an electronic medical record system and included patients were followed up for 1 year. Participants were included according to the following criteria: (1) all patients presented with back or radicular pain refractory and received physical or medical treatment for 4-8 weeks;

Participants and Study Design
(2) patients had a preoperative evaluation with a detailed neurological examination and radiological examinations, including dynamic lumbar radiography (flexion and extension) and static (anterior-posterior and lateral), lumbar MRI, or CT. Participants were excluded according to the following criteria: (1) patients with multi-level lumbar disk degeneration; (2) patients with previous lumbar spine surgery; and (3) patients with diagnoses of spine fractures, tumors, and infections or acute spinal trauma.

Data Preparation and Collection
Before clinical data collection, written informed consent from all the patients was obtained. Demographic characteristics, including age, gender, body mass index (BMI), and comorbidities before surgery were recorded for later analysis.
Ultimately, detailed information about neurological examination, outcome measures, and clinical evaluation of TLIF were collected as well.

Clinical Evaluation of TLIF
Oswestry Disability Index (ODI) Oswestry Disability Index (ODI) is a principal conditionspecific outcome measure used in the management of spinal disorders and to assess patient progress in routine clinical practice. The ODI score system includes 10 sections: pain intensity, personal care, lifting, walking, sitting, standing, sleeping, sex life, social life, and traveling. For each section (consisting of six statements), the total score is 5. Intervening statements are scored according to rank. If more than one box is marked in each section, take the highest score. If all 10 sections are completed, the score is calculated as follows: total scored out of total possible score-Â 100. If one section is missed (or not applicable), the score is calculated as: (total score/ (5 Â number of questions answered)) Â 100%. A score of 0%-20% is considered mild dysfunction, 21%-40% is considered moderate dysfunction, 41%-60% is considered severe dysfunction, and 61%-80% is considered disability. For cases with a score of 81%-100%, they are either long-term bedridden or exaggerating the impact of pain on their lives. 28 Pain Measurement (Visual Analog Scale) The outcomes of symptoms were evaluated through followup interviews at 6 weeks, 6 months, and 1 year after surgery. Low back pain and leg pain were measured using the Visual Analog Scale (VAS) score. It is a continuous scale with a score of zero representing no pain and a score of 10 representing the worst pain. 29 Assessment of the Severity of Clinical Symptoms (JOA Scores) Japanese Orthopaedic Association (JOA) scores were used to assess the severity of clinical symptoms. It is comprised of six domain scores, which are motor dysfunction in the upper extremities, motor dysfunction in the lower extremities, sensory function in the upper extremities, sensory function in the trunk, sensory function in the lower extremities, and bladder function, scaling from 0 to 4, 4, 2, 2, 2, and 3, respectively. The minimum total score is zero and the maximum total score is 17.
The following indicators were conducted to accomplish the clinical evaluation of TLIF: ODI, VAS scores for back pain and leg pain, JOA scores, and the JOA recovery rate (%). They were performed to assess the preoperative and postoperative pain in the back and legs and daily life functions. Data were collected before the operation, at 1 month, 3 months, 6 months, and 1 year after surgery. VAS data for back pain 3 and 7 days after surgery were collected. Postoperative complications were also recorded (e.g., urinary tract infection, deep venous thrombosis, or surgical site infection).

Surgical Techniques
For both groups of patients, the operation was performed by the same surgeons. The W-TLIF utilized a midline open approach and notched a single incision through the Wiltse bilateral approach. Subcutaneous tissue was exposed through the intervertebral joint bilateral muscle space, and the assist of the lamina. The operator avoided extensive peeling of the paraspinal musculature and preserved well posterior ligamentous complex. 30 Minimally invasive surgical instruments for the MET-Rx Microsightoscopy System (Medtronic), Viperl Percutaneous Pedicle Screw Internal Syndromes (DePuy), and Concorde bullet intervertebral fusion and minimally invasive surgical instruments (DePuy) were applied for the implement of ME-TLIF. A representative case and ME-TLIF surgery operation are shown in Figure 2. The surgical steps were as follows: 1. Operative position. Patients were given general anesthesia and then were placed in a prone position. 2. Nailing positioning. The center of the vertebral pedicle was identified by the needle of the c-shaped arm X-ray. 3. Clearance of the disc. With the help of the perspective, the Jamshidi needle was placed in the outer part of the pedicle (3 o'clock or 9 o'clock position) and slowly pulled out the needle core via the MET-Rx microendoscopic system. The intervertebral disc tissue was cleaned.
4. Implant Cage. The cage filled with the cancellous bone was then inserted obliquely into the intervertebral space through the working cannula.  and a brief description of surgery procedure 3303 ORTHOPAEDIC SURGERY VOLUME 14 • NUMBER 12 • DECEMBER, 2022 5. Set Screw. After removing the MET-Rx working channel, the guide needle was percutaneously expanded, then a 6 mm Viperl pedicle screw was screwed and tapped. We used the same method to screw in the other three screws. An appropriate length of the rod was inserted into the subcutaneous tissue. Then the stick was removed and the nut was screwed. The same method was applied to the opposite side.
The visualization process of surgery is shown in Figure 3.

Statistical Analysis
All data were collected retrospectively. Statistical analysis was performed using the SPSS version 10.0. Continuous variables were described as mean AE standard deviation (x AE s) and the categorical variables were presented as sum and percentage (n, %). The Pearson chi square test or Fisher exact test were

Demographic Characteristics of Included Patients
Fifty-seven patients were included in the study, with 26 eligible patients in the ME-TLIF group and 31 eligible patients in the W-TLIF group. No patients were excluded due to incomplete follow-up data. Table 1 and Table 2 describe the demographic characteristics of patients in the two groups. There were no statistical differences in terms of age, gender, body mass index, lumbar fusion position, scores of scales, and comorbidities between the two groups (p > 0.05).

Intraoperative Findings
The details of the operation were as follows: (1)

Comparison of Postoperative Metrics
Blood Loss, Operation Duration, and Fluoroscopy Time Intraoperative blood loss and postoperative drainage in the ME-TLIF group were significantly less than those in the  Abbreviations: ME-TLIF, microendoscopy-assisted transforaminal lumbar interbody fusion; W-TLIF, Wiltse approach-transforaminal lumbar interbody fusion W-TLIF group (p < 0.05). All patients did not receive postoperative or intraoperative blood transfusions. The time lengths of intraoperative fluoroscopy were significantly longer in the ME-TLIF group than in the W-TLIF group, with a medium of 71.2 s in the ME-TLIF group and 14.4 s in the W-TLIF group, respectively (t = 4.272, p < 0.001). The operation duration in the ME-TLIF group was longer than that in the W-TLIF group (t = 2.969, p < 0.05) ( Table 4). Tables 3, 4, and 5 described the spine and lumbar level fusion of patients in the two groups, and it showed a statistical difference between the two groups in spinal fusion position (t = 2.015, p < 0.05). The median number of hospitalization days was 9.04 in the ME-TLIF group and 11.29 in the W-TLIF group, respectively (t = 2.535, p < 0.05).

Clinical Outcomes Comparison of Included Patients
Oswestry Disability Index (ODI), Japanese Orthopaedic Association (JOA), and visual analog score (VAS) Patients in the ME-TLIF and W-TLIF groups were followed up for 1 year. ODI, JOA, and VAS scores at the latest visit  were better than those before the surgery in both groups (p < 0.05). Postoperative VAS of back pain in the ME-TLIF group on day 3 and 7 were significantly less than those in the W-TLIF group (p < 0.05). However, there were no differences in postoperative pain at other observed time points between the two groups. There were also no significant differences in JOA, JOA recovery rate, and ODI score between the two groups at all time points after surgery (Tables 5 and 6).

Bony Fusion Outcomes Comparison of Included Patients
In terms of bony fusion, radiographs were used as the measurement method. Based on Bridwell's criterion, at 6 months, 61.50% of patients achieved grade I fusion and 38.50% of patients achieved grade II fusion in the ME-TLIF group. A total of 54.80% of patients achieved degree I fusion and 45.20% of patients achieved grade II in the W-TLIF group (p = 0.923) ( Table 7). After 1 year, 92.31% of patients in the ME-TLIF group and 87.1% of patients in the W-TLIF group achieved grade I fusion (p = 0.632) ( Table 8). All of the above showed no statistical differences between the two groups. The patients with grade II fusion are still under follow-up. A representative case is shown in Figure 4.

Complications in the Two Groups
There were no patients who suffered severe life-threatening complications on account of the surgery. However, three perioperative complications were reported in the W-TLIF group. The right L5 root palsy of one case had no significant improvement after operation because the pedicle position was compressed by the thecal sac. As a result, she experienced a revision operation that rearranged the pedicle screws and finally recovered completely within 3 months after the operation. One patient was recorded with a urinary tract infection but was successfully treated with antibiotics. The third case had a superficial wound because of an injection and was given dressing nursing every day. Two weeks later, the wound healed well, and the patient was successfully discharged.

Discussion
The Superiority of the MIS-TLIF In order to reduce the damage to posterior midline spinal structures, Foley et al. introduced the concept of minimally invasive TLIF, a modification of PLIF, 22 which had less damage to paravertebral muscles compared with conventional TLIF. In 2005, Mummaneni 31 proposed the application of Medtronic's expandable minimally invasive approach for minimally invasive TLIF surgery. Yan et al. 20,24,32 performed this procedure with the assistance of an intervertebral disc endoscope without lamina injury, or exposing and pulling of the dural sac and nerve root. Zhou et al. 33 carried out the technology in China with micro-endoscopic assistance. Compared with the traditional TLIF, MIS-TLIF provides a higher magnification, a wider vision field, higher resolution images, and a safer and less complicated operation with small trauma, little bleeding, and better curative effect.

Clinical Outcome
Lower Blood Loss in ME-TLIF Surgery In this study, we performed decompression and bone graft fusion surgery via the working sleeve of the METRx disc system without other supporting expandable sleeves. Its 18 mm diameter was smaller than all of the current expandable channel diameters without the bottom expansion, so the paravertebral muscle stretch expansion can be significantly reduced. Compared with W-TLIF surgery, blood loss volume during or after surgery was significantly less in ME-TLIF surgery. No patients required blood transfusions during or after surgery. In addition, surgical recovery in the ME-TLIF group was faster than that in the W-TLIF group. The rehabilitation time of ambulation and the postoperative hospitalization duration were shorter, but there was no significant difference in hospitalization expenses.

VAS, ODI, and JOA Scores all Improved
Previous studies have shown that postoperative low back pain may be caused by excessive multifidus muscle checkpoint stripping, resulting in scarring of muscle fibers, decreased muscle function, poor back muscle function recovery after surgery, 11 and long hospitalization duration. Our study showed that the VAS (back and leg pain), ODI, and JOA scores of both groups were significantly improved compared with those before surgery, but the VAS of the back pain score for initial postoperative pain in the ME-TLIF group was lower than that in the W-TLIF group. Figures 5  and 6 show that after ME-TLIF surgery, the patient's symptoms were significantly relieved, and the VAS, ODI, and JOA scores were significantly improved, and adequate decompression of the nerve was confirmed by reexamination of the MRI.

Longer Radiation Exposure Time during ME-TLIF
In the present study, discectomy and placement of pedicle screws through a small tubular corridor led to more difficulty in the ME-TLIF surgical technique than in MIS-TLIF surgery. With the lack of proficiency in the operation and limited space for the operation, we needed to repeatedly confirm the screw position during surgery, resulting in an increase in intraoperative fluoroscopy time. 34 Bindal 35 did a prospective study about the time and dose of radiographic exposure during MIS-TLIF surgery. It showed that the mean fluoroscopy time was 1.69 min per case (a range of 0.82-3.73 min). However, the results of this study showed that the radiation exposure time was lower than that in Bindal's study. We also found that radiation exposure time in the ME-TLIF group was significantly higher than that in the W-TLIF group.
Smaller Incision with ME-TLIF With the continuous development of minimally invasive spine surgery, micro-endoscopic discectomy (MED) is widely used as an extremely mature and minimally invasive technique. Isaacs firstly applied the combination of endoscopic discectomy and intervertebral fusion in TLIF surgery, which better protected the multifidus muscle, paravertebral muscles, and soft tissues. However, endoscopic microsurgery assisted by percutaneous MIS-TLIF surgery has higher technical requirements due to the limited diameter of the endoscopic working channel and the relatively small operating range. 25 The minimally invasive surgery protected the multifidus muscle and other paravertebral muscles through expansion of the working channel. 25 ME-TLIF was able to minimize iatrogenic soft tissue and muscle injuries around the spine. In the ME-TLIF group, we only notched four 1 cm incisions to expand the paravertebral muscles. In contrast, W-TLIF surgery requires a large midline incision and long-term muscle distraction through the retractor. Thus, most of the patients in the ME-TLIF group started rehabilitating earlier, recovered sooner, and had a shorter hospitalization duration. When comparing the fusion of two groups, there was no significant difference between the two groups when followed up to 1 year. A representative case of interbody fusion 1 year after ME-TLIF surgery is shown in Figure 7.

No Perioperative Complications in ME-TLIF
In the present study, none of the patients in the ME-TLIF group had perioperative complications. In contrast, one urinary tract infection, one incision infection, and one wrong placement of a screw occurred in the W-TLIF group. The reported rate of complications varied between 9.5% and 52% for the W-TLIF procedure and between 0.6% and 31.6% for MIS-TLIF. 36 Due to the small sample size, postoperative complications were not formally accepted as a part of this study.

Technical Advantages and Experience
Advantages: (1) compared with W-TLIF, ME-TLIF better protects paravertebral muscles (because the incision is smaller and the stripping range is more limited); Preoperative MRI grading of Pfirrmann lumbar disc herniation was grade IV. (C) and (D) showed no disc herniation observed in the MRI of the lumbar spine 1 year after the microendoscopy-assisted transforaminal lumbar interbody fusion surgery, the height of the intervertebral space was restored, and the symptoms of lumbar and leg pain were relieved.
(2) compared with W-TLIF, the bleeding volume of ME-TLIF is smaller. In addition to the smaller stripping range, it may be related to the placement of the working cannula that can compress muscle tissue and avoid blood leakage between muscles; (3) ME-TLIF has less drainage flow and early drainage and extraction time, which is conducive to the patient's recovery as soon as possible; and (4) there is less low back pain caused by intraoperative muscle stripping after ME-TLIF, and the patient goes to the ground earlier, which is also conducive to the patient's recovery as soon as possible. Experience: (1) after placing the body position, try to use the perspective positioning of the G-arm and insert Kirschner wire to shorten the nail placement time. If there is no G-arm, two C-arms can also be used to cross place fluoroscopy; (2) when placing the working channel, it is necessary to locate the main parts accurately; and (3) fluoroscopy may still be needed before dealing with the endplate because the previous decompression operation may have made the channel swing. It is necessary to confirm that the channel is parallel to the intervertebral space, so as to avoid endplate injury.
Limitation of ME-TLIF Some limitations may not be ignored in this study. First, the sample size in this retrospective study was small, so further multicenter prospective studies with a larger sample size are required to confirm our results. Second, the inclusion criteria of patients in this study are not complete. Patients with multiple lumbar spinal canal stenosis and lumbar spondylolisthesis should be further studied in future research.

Conclusion
In summary, microendoscopy-assisted ME-TLIF provides patients with more beneficial perioperative clinical outcomes compared with W-TLIF. Despite the fact that both surgical methods improved fusion rates, ODI, and VAS, microendoscopy-assisted ME-TLIF is superior to W-TLIF in terms of less iatrogenic injury, less intraoperative or postoperative blood loss, and earlier rehabilitation. We will overcome the indiscriminate disadvantages of microendoscopy-assisted ME-TLIF on increased operative duration and radiologic exposure in the future. We also anticipate that the difference in surgical time between the two groups will be gradually reduced.

Conflicts of Interest
T he authors have no conflicts of interest to declare.

Ethics Statement
T he experimental protocols were approved by Ethics Committee of Fujian Medical University Union Hospital (reference number: 2020KY0016).