Abstract
Objectives
To evaluate the effectiveness and safety of interlaminar versus transforaminal endoscopic lumbar discectomy (IELD versus TELD) in treating L4/5 highly migrated lumbar disc herniation (HM-LDH), and to analyze factors influencing surgical approach selection.
Methods
From January 2022 to June 2024, patients with L4/5 HM-LDH treated with IELD or TELD were retrospectively included. Patients were divided into two groups based on the approach used: IELD (under general anesthesia) and TELD (under local anesthesia with intravenous sedation). Baseline data, perioperative data, radiological data, patient-reported outcomes (PROs) including the visual analogue scale (VAS), Oswestry Disability Index (ODI), and modified MacNab criteria were recorded. All data were compared and analyzed by independent t-tests and χ² tests.
Results
There were 50 patients in the IELD group and 80 patients in the TELD group respectively. The baseline data between the two groups did not show significant difference. The IELD group had relatively wider interlaminar window and thinner intervertebral foramen at L4/5, while there is no significant difference in the height of the intervertebral foramen between the two groups. No significant differences were found in intraoperative blood loss and postoperative length of stay. However, IELD had a shorter operation time (86.6 ± 12.6 min vs.99.4 ± 27.4 min, P < 0.001) and less fluoroscopy times (4.3 ± 1.1 vs. 11.6 ± 1.9, P < 0.001) compared to TELD. Both groups achieved a significant improvement in VAS and ODI after surgery. Satisfaction rates were 92.0% for IELD and 91.3% for TELD (P = 0.816) according to the modified MacNab criteria. As compared to preoperative measurements, both groups showed a significant reduction in the anteroposterior diameter of the intervertebral disc (APDID) and a significant increase in dural sac cross-sectional area (DSCA) at 12 months postoperatively. No significant differences in complications were observed between the two groups. Regarding residual symptoms, there were more patients in the TELD group who reported residual back pain (VAS ≥ 2) during the follow-up periods (33.8% vs. 16.0%, P = 0.026).
Conclusion
Both IELD and TELD can achieve satisfactory clinical and radiological outcomes in treating L4/5 HM-LDH. IELD has advantages of shorter operation time, less fluoroscopy times and fewer residual back pain compared with TELD. Selection of surgical approach for L4/5 HM-LDH depends on anatomical structure, migration characteristics, and the operative skills of the surgeon.
Keywords: Highly migrated lumbar disc herniation, percutaneous endoscopic lumbar discectomy, interlaminar approach, transforaminal approach
Introduction
Lumbar disc herniation (LDH) is a common degenerative spine disorder that causes back pain, radicular leg pain, and disability. Herniated disc fragments, once extruded, might migrate into the spinal canal either upward or downward [1]. Among them, highly migrated LDH (HM-LDH) is the most challenging for spine surgeons. Open fenestration discectomy is traditionally indicated for HM-LDH, but during the surgery, a substantial quantity of soft tissue has to be dissected and a large laminotomy are unavoidable to overcome the anatomic barrier [2, 3], which may lead to iatrogenic segmental instability and related complications [4, 5].
Recently, percutaneous endoscopic lumbar discectomy (PELD) has attracted more and more attention as a minimally invasive spinal surgery, including two classical approaches, such as interlaminar endoscopic lumbar discectomy (IELD) and transforaminal endoscopic lumbar discectomy (TELD) [6]. Zhao et al. [7] compared IELD and TELD for L4/5 LDH and found comparable clinical outcomes in terms of pain relief and disability improvement via either approach. Generally, IELD is preferred for the segment with a large interlaminar space, such as L5/S1 [8]. Conversely, TELD is usually selected for the segment with a larger intervertebral foramen such as LDH at L4/5 or above [9]. Dezawa et al. [2]. advocated that the interlaminar approach was suitable for HM-LDH, but it was necessary to select a large bone window to insert the endoscope. Sun et al. [10] treated LDH with different grades of migration using TELD, achieving favorable clinical outcomes. However, for cases with high-grade migration, foraminoplasty may be inevitable. Although many endoscopic surgical approaches have been proposed, when dealing with L4/5 HM-LDH, due to its unique location and anatomical characteristics, spinal surgeons often hesitate in the selection of IELD or TELD.
Some scholars have previously attempted percutaneous endoscopic treatments for HM-LDH. Shen et al. [11] treated 63 cases of very high-grade migration by TELD combined with targeted puncture and foraminoplasty techniques, resulted in significant postoperative symptom improvement. Khandge et al. [12] proposed a modified interlaminar approach, which avoided the flavectomy and maintain the integrity of the natural spinal anatomy. Some scholars have also suggested that a combined interlaminar and foraminal approach [13]. However, there was limited comparative research on these two approaches for the treatment of L4/5 HM-LDH. Furthermore, few studies strictly analyzed preoperative radiological factors that affect the approach selection.
Therefore, in this study, we retrospectively reviewed a cohort of L4/5 HM-LDH patients treated with either IELD or TELD, and compared the radiological and clinical outcomes of these two full-endoscopic techniques, aiming to provide a reference for the selection of an appropriate surgical approach for this particular pathology.
Methods
We retrospectively reviewed a cohort of patients diagnosed with L4/5 HM-LDH who underwent PELD in our hospital between January 2022 and June 2024 (Fig. 1). This study was approved by the ethics committee of our hospital (2025-0289-01). The inclusion criteria were (1) Obvious lumbar and leg pain without significant improvement after 6 weeks of standard conservative treatment; (2) L4/5 HM-LDH confirmed by magnetic resonance imaging (MRI) according to grade system defined by Ahn et al. [14] (Fig. 2); (3) Patients who received either IELD or TELD; (4) The procedures were performed by the same chief surgeon; and (5) With continuous follow-up for more than one year. The exclusion criteria were (1) One or more segments of LDH in addition to L4/5 requiring surgical treatment; (2) Lumbar spine instability or spondylolisthesis; (3) Previous spinal surgery at L4/5; (4) Extraforaminal or calcified LDH; and (5) Cauda equina syndrome.
Fig. 1.
The flow chart of patient selection and grouping process
Fig. 2.
Schematic illustration of the six migrated lumbar disc herniation grades in the sagittal plane, as divided by Ahn et al. Notes: The light red area refers to the HM-LDH mentioned in this study
Finally, 130 patients were included in this study. They were divided into IELD group and TELD group according to the approaches used. All patients underwent follow-up for more than one year. The average follow-up in the IEDL group was 22.2 ± 5.8 months (range: 12–32 months), and in the TELD group, 23.6 ± 6.7 months (range: 12–36 months).
Preoperative radiological assessment
Preoperative magnetic resonance imaging (MRI) and computed tomography (CT) were performed to determine the characteristics including side of LDH, direction and grade of migration. In addition, preoperative anteroposterior and lateral radiographs of the lumbar spine were used to evaluate the parameters of the interlaminar window and intervertebral foramen, including height, width, and area, with specific measurement methods shown in Fig. 3. Two experienced physicians independently performed all radiological assessments on the Picture archiving and communication system (PACS). The average of three measurements was taken as the measurement result, with a measurement precision of 0.1 mm. The final value for statistical analysis was obtained by using the average of the measurements from the two physicians.
Fig. 3.
Preoperative radiological assessment of the interlaminar window and intervertebral foraminal. A The width of interlaminar window was measured as the distance from the inner edge of the inferior and superior articular processes to the spinous process (solid line). The height of interlaminar window was measured as the vertical distance between the highest point of the lower margin of the lamina and the lowest point of the upper margin of the lamina of the adjacent inferior vertebra (dotted line). B The area of laminar window on the left and right sides were delineated in the PACS. C The height of intervertebral foraminal was measured as the maximum distance between the inferior margin of the pedicle of the superior vertebra and the superior margin of the pedicle of the inferior vertebra (solid line). The width of intervertebral foraminal was measured as the shortest distance between the superior edge of the superior articular process of the caudal vertebra and the posterior edge of the inferior endplate of the cranial vertebra (dotted line). D The area of intervertebral foraminal was delineated in the PACS. Notes: The colors of these pictures are used to distinguish between the left and right sides, with yellow representing the left side and red representing the right side
Surgical technique
All surgeries were performed by the same surgeon (X.S), who has 4 years of experience and over 2,000 cases of minimally invasive surgeries, with an annual surgical volume of approximately 600 cases. Additionally, the surgeon has performed over 1,000 cases of both IELD and TELD. Generally, patients with high iliac crest or wider interlaminar window were preferred for IELD, while patients with foraminal LDH, low iliac crest, or smaller interlaminar window were preferred for TELD.
Interlaminar approach
The procedure was performed under general anesthesia. The patient was positioned in the prone position on a radiolucent table, with mild genuflexion and hip flexion to enlarge the interlaminar space and facilitate access to the surgical site.
The C-arm fluoroscopy was used to confirm the optimal placement of the puncture needle, and the entry site was determined based on the direction and extent of the migrated nucleus pulposus. Generally, the entry point was located at the midpoint of the line connecting the midpoint of the target intervertebral space and the furthest end of the migrated nucleus pulposus. A 1.2-cm-length incision was made and a series of soft tissue dilators were introduced. A working cannula was then placed into the interlaminar space, with fluoroscopic guidance ensuring accurate placement. After that, the endoscope (iLESSYS-Delta, Joimax, Germany) was inserted through the cannula. The ligamentum flavum was identified, and laminotomy was performed by a high-speed burr and a Kerrison rongeur under direct visualization. In cases with very high-grade migration, it was necessary to do a wide laminotomy to enlarge the interlaminar window, with careful attention to preserving the stability of the facet joint and ensuring the integrity of the pars.
After entering the spinal canal, the nerve root, the dural sac and the migrated nucleus pulposus were identified. Then the nerve root was carefully explored by adjusting the working cannula. The migrated nucleus pulposus was then completely removed by forceps, with the angle of the endoscope adjusted to ensure complete visualization and removal. The radiofrequency electrode was used intraoperatively to ablate the ruptured annulus fibrosus, promoting its contraction and shaping, further reducing compression on the nerve root. At the same time, it was employed for hemostasis. After ensuring complete decompression of the nerve roots and relaxation of the dural sac, the endoscope and the working cannula were removed, and the wound was sutured with no need for drainage.
Transforaminal approach
The procedure was performed under local anesthesia (10 ml of 1% lidocaine and 10 ml of 0.75% ropivacaine) combined with intravenous sedation (A loading dose of 1 µg/kg dexmedetomidine was administered via intravenous infusion over 10 min, followed by maintenance at 0.5 µg/kg/h until wound suturing.) The patient was placed in the same prone position as IELD. Based on the C-arm fluoroscopy, the horizontal line of the affected intervertebral disc and the posterior midline of the spine were marked to determine the precise puncture point. The entry point was usually located 8–10 cm lateral to the midline, and the puncture direction was slightly tilted (15–25 degrees) according to the patient’s body type and the anatomical position of the migrated nucleus pulposus. Generally, the direction was designed more tilted for a downward migration and less tilted for an upward migration to ensure accurate targeting at the desired area.
Local infiltration anesthesia was performed layer by layer. An 18-gauge needle was then accurately punctured to the articular process area under C-arm fluoroscopy, ensuring precise needle tip placement. Once the needle tip position was confirmed, a guidewire was placed through the needle. Subsequently, a 7 mm-length incision was made. A series of soft tissue dilators were gradually placed. Then a working cannula and a spinal endoscope (TESSYS, Joimax, Germany) were introduced. If necessary, visualization techniques were used to perform foraminoplasty, and part of the lateral-ventral edge of the superior articular process was removed to enlarge the working area. Under endoscopic guidance, the neural structures and migrated nucleus pulposus were identified. Subsequently, the forceps were used to remove the migrated nucleus pulposus and the probe was used to ensure the relaxation of the nerve root. At the same time, attention was paid to patients’ comfort. Throughout the procedure, a radiofrequency electrode was employed for hemostasis. After ensuring complete decompression of the nerve root and relaxation of the dural sac, the endoscope and the working cannula were removed, and the wound was sutured with no need for drainage.
Postoperative management
Standard postoperative treatment was administered, including medication measures to alleviate pain and reduce swelling. After surgery, all patients were guided to perform lumbar and lower limb functional exercises at bed. After 24 h of bed rest, they were encouraged to sit and then to ambulate under the assistance of a waist brace. They were advised to avoid excessive lifting, bending, and twisting for one month, and also to incorporate moderate lumbar and back muscle exercises into their daily routine activities. All patients underwent regular follow-up lumbar MRI examinations at 3 months and 12 months after the surgery to assess the condition of disc.
Evaluation indicators
Clinical data including operation time, intraoperative blood loss, fluoroscopy times, postoperative length of stay and perioperative complications were collected. Operation time was defined as the time from patient positioning to the closure of the incision, including the time for establishing the channel and fluoroscopy. Intraoperative blood loss was estimated based on the amount of blood absorbed by surgical drapes and suction. Fluoroscopy times was recorded immediately after the surgery. Postoperative length of stay was defined as the time from surgery to discharge. Complications were recorded. Intraoperative complications included dural tear, nerve root irritation and facet joint injury. Postoperative complications included early wound infection, neurological deficit such as decreased muscle strength or impaired sphincter function. Complications during follow-up included residual back pain and recurrence, residual back pain was defined as the visual analog scale (VAS) for back pain ≥ 2 at final follow-up, according to the previous literature [15].
Patient-reported outcomes (PROs) were evaluated using VAS for back and leg pain, and Oswestry Disability Index (ODI). Patient satisfaction was assessed by the modified MacNab criteria at the final follow-up.
Preoperative and 12-month postoperative lumbar MRI T2-weighted axial images were used to measure the anteroposterior diameter of the intervertebral disc (APDID) and dural sac cross-sectional area (DSCA) of the surgical segment through PACS to assess the effectiveness of the decompression (Fig. 4).
Fig. 4.
Schematic diagram for measuring disc size and spinal canal area. A and B The anteroposterior diameter of the intervertebral disc (APDID) at the surgical segment was measured on axial MRI of lumbar spine. The distance from the farthest point of the disc protrusion into the spinal canal to the anterior edge of the disc was recorded, which was indicated by a red bidirectional arrow. The preoperative distance was d, and the postoperative distance was d’. The reduction percentage was calculated as (d-d’)/d×100%; C and D The red area represents the dural sac cross-sectional area (DSCA), which was measured on lumbar MRI. Preoperatively, it was recorded as S, and postoperatively as S’. The increase percentage was calculated as (S’-S)/S×100%
Statistical analysis
SPSS (Version 27.0, Chicago, USA) statistical software was applied for data analyses. Shapiro-Wilk method was used to estimate the normal distribution of data. Continuous variables were expressed as means ± SDs. Independent t-test was used to compare the difference in age, BMI, preoperative symptom duration, radiological data, perioperative data, VAS, and ODI between IELD and TELD groups. Categorical variables were expressed as number. Gender, smoker, alcohol consumption, diabetes, hypertension, condition of migration (side, direction and grade), modified MacNab evaluation, complications and residual back pain between groups were evaluated by the χ² test. Use multivariate regression analysis to identify independent risk factors for postoperative residual back pain. Variables were selected based on clinical relevance and previous literatures [16–18]. Line charts and pie charts were generated through Prism 10 software (GraphPad Software, San Diego, California, USA). P < 0.05 was considered statistically significant.
Results
General information
Table 1 shows the baseline characteristics of the patients in both groups. There were 50 patients (29 males and 21 females) in the IELD group, while 80 patients (45 males and 35 females) in the TELD group. All baseline demographic characteristics did not significantly differ between the two groups. The typical cases of IELD and TELD are presented in Figs. 5 and 6.
Table 1.
Comparison of demographic characteristics between IELD and TELD groups
| Cohort details | IELD group (n = 50) | TELD group (n = 80) | t or χ² value | P-value |
|---|---|---|---|---|
| Age, (years) | 47.5 ± 13.1 | 44.7 ± 14.0 | 1.12 | 0.267 |
| Range | 22–69 | 18–77 | ||
| Gender, n (%) | 0.04 | 0.845 | ||
| Male | 29 (58.0%) | 45 (56.2%) | ||
| Female | 21 (42.0%) | 35 (43.8%) | ||
| BMI, (kg/m2) | 24.8 ± 3.7 | 24.6 ± 3.4 | 0.37 | 0.711 |
| Range | 17.8–37.5 | 17.6–37.5 | ||
| Smoker, n (%) | 0.40 | 0.526 | ||
| Nonsmoker | 39 (78.0%) | 66 (82.5%) | ||
| Smoker | 11 (22.0%) | 14 (17.5%) | ||
| Alcohol consumption, n (%) | 0.27 | 0.641 | ||
| Non | 35 (70.0%) | 62 (77.5%) | ||
| Occasional (≤ 2 times a week) | 12 (24.0%) | 14 (17.5%) | ||
| Frequent (≥ 3 times a week) | 3 (6.0%) | 4 (5.0%) | ||
| Diabetes, n (%) | 1.25 | 0.263 | ||
| No | 44 (88.0%) | 76 (95.0%) | ||
| Yes | 6 (12.0%) | 4 (5.0%) | ||
| Hypertension, n (%) | 0.12 | 0.724 | ||
| No | 42 (84.0%) | 69 (86.2%) | ||
| Yes | 8 (16.0%) | 11 (13.8%) | ||
| Preoperative symptom duration, (months) | 4.1 ± 3.4 | 4.9 ± 3.7 | -1.28 | 0.203 |
| Follow-up time (months) | 22.2 ± 5.8 | 23.6 ± 6.7 | -1.24 | 0.289 |
Abbreviations: BMI Body mass index
Fig. 5.
A patient in IELD group with low back pain and right leg pain for 2 months, which was treated by IELD. A and B, Preoperative MRI scans showing L4/5-disc herniation with very high-grade migration. C and D, Photographs obtained during the surgery. E and F, MRI obtained 15 months after the operation
Fig. 6.
A patient in TELD group with low back pain and right leg pain for 4 months, which was treated by TELD. A and B, Preoperative MRI scans showing L4/5-disc herniation with high-grade migration. C and D, Photographs obtained during the surgery. E and F, MRI obtained 20 months after the operation
Preoperative radiological data
We then compared the preoperative plain radiographs, MRI, and CT images between the two groups and attempted to identify the factors that affected the approach. In the IELD group, there were 8 patients with upward migration and 42 patients with downward migration. In the TELD group, there were 12 patients with upward migration and 68 patients with downward migration. The proportion of very high-grade migration was slightly higher in the IELD group compared to the TELD group (40% vs. 27.5%), although there was no statistically significant difference (P = 0.138, Table 2).
Table 2.
Comparison of preoperative and postoperative radiological characteristics between IELD and TELD groups
| Variables | IELD group (n = 50) | TELD group (n = 80) | t or χ² value | P-value |
|---|---|---|---|---|
| Side of LDH, n (%) | 2.17 | 0.140 | ||
| Left | 31 (62.0%) | 39 (48.8%) | ||
| Right | 19 (38.0%) | 41 (51.2%) | ||
| Direction of migration, n (%) | 0.02 | 0.878 | ||
| Upward | 8 (16.0%) | 12 (15.0%) | ||
| Downward | 42 (84.0%) | 68 (85.0%) | ||
| Grade of migration, n (%) | 2.20 | 0.138 | ||
| High | 30 (60.0%) | 58 (72.5%) | ||
| Very high | 20 (40.0%) | 22 (27.5%) | ||
| Interlaminar window | ||||
| Height (mm) | 11.7 ± 2.6 | 10.3 ± 2.7 | 2.99 | 0.003* |
| Width (mm) | 12.2 ± 2.9 | 10.9 ± 3.7 | 2.07 | 0.004* |
| Area (mm2) | 114.6 ± 19.6 | 98.5 ± 31.3 | 3.60 | < 0.001 * |
| Intervertebral foramen | ||||
| Height (mm) | 18.6 ± 3.3 | 19.7 ± 2.7 | -1.76 | 0.082 |
| Width (mm) | 7.2 ± 2.1 | 8.3 ± 2.5 | -2.64 | 0.009* |
| Area (mm2) | 119.0 ± 49.3 | 149.2 ± 53.3 | -3.23 | 0.002* |
| APDID (mm) | ||||
| Preoperative | 43.5 ± 4.2 | 43.4 ± 3.4 | 0.05 | 0.960 |
| 12 months follow-up | 37.3 ± 5.8 | 37.7 ± 3.0 | -0.46 | 0.647 |
| Reduction (%) | 14.8 ± 11.3 | 13.2 ± 3.9 | 1.21 | 0.228 |
| DSCA (mm2) | ||||
| Preoperative | 124.2 ± 44.3 | 124.5 ± 33.8 | -0.05 | 0.962 |
| 12 months follow-up | 177.7 ± 51.7 | 174.3 ± 38.9 | 0.39 | 0.698 |
| Increase (%) | 52.4 ± 46.3 | 44.1 ± 24.3 | 1.35 | 0.181 |
Abbreviations: LDH Lumbar disc herniation, APDID Anteroposterior diameter of the intervertebral disc, DSCA Dural sac cross-sectional area
*P < 0.05
Of note, the IELD group had a larger interlaminar window height (11.7 ± 2.6 mm vs. 10.3 ± 2.7 mm, P = 0.003), width (12.2 ± 2.9 mm vs. 10.9 ± 3.7 mm, P = 0.004), and area (114.6 ± 19.6 mm² vs. 98.5 ± 31.3 mm², P < 0.001). The TELD group had a significantly larger intervertebral foramen width compared to the IELD group (8.3 ± 2.5 mm vs. 7.2 ± 2.1 mm, P = 0.009) and area (149.2 ± 53.3 mm² vs. 119.0 ± 49.3 mm², P = 0.002), while there was no significant difference in the height of the foramen (19.7 ± 2.7 mm vs. 18.6 ± 3.3 mm, P = 0.082).
Perioperative data
As shown in Table 3, the IELD and TELD groups exhibited comparable intraoperative blood loss (14.6 ± 6.8 ml vs. 13.2 ± 7.7 ml, P = 0.289) and postoperative length of stay (2.8 ± 0.6 days vs. 2.6 ± 0.9 days, P = 0.292). However, the average operation time in the IELD group was 86.6 ± 12.6 min, which was significantly shorter than the 99.4 ± 27.4 min in the TELD group (P < 0.001). The average fluoroscopy times was 4.3 ± 1.1 in the IELD group, which was significantly fewer than the 11.6 ± 1.9 in the TELD group (P < 0.001). Of note, in the further analysis of the IELD and TELD groups, very high-grade migration showed a slight trend of increased operation time, intraoperative blood loss, and fluoroscopic times compared to high-grade migration, though no significant statistical differences were observed (P > 0.05).
Table 3.
Comparison of perioperative data and complications between IELD and TELD groups
| Variables | IELD group (n = 50) | TELD group (n = 80) | t or χ² value | P-value |
|---|---|---|---|---|
| Operation time (min) | 86.6 ± 12.6 | 99.4 ± 27.4 | -3.62 | < 0.001* |
| Intraoperative blood loss (ml) | 14.6 ± 6.8 | 13.2 ± 7.7 | 1.06 | 0.289 |
| Fluoroscopy times | 4.3 ± 1.1 | 11.6 ± 1.9 | -28.20 | < 0.001* |
| Postoperative length of stay (days) | 2.8 ± 0.6 | 2.62 ± 0.9 | 1.06 | 0.292 |
| Intraoperative, n (%) | ||||
| Dural tear | 1 (2.0) | 0 (0.0) | 0.00 | 1.000 |
| Nerve root irritation | 0 (0.0) | 1 (1.3) | 0.00 | 1.000 |
| Facet joint injury | 1 (2.0) | 2 (2.5) | 0.00 | 1.000 |
| Postoperative, n (%) | ||||
| Early wound infection | 0 (0.0) | 0 (0.0) | 0.00 | 1.000 |
| Neurological deficit | 0 (0.0) | 0 (0.0) | 0.00 | 1.000 |
| Follow-up, n (%) | ||||
| Residual back pain | 8 (16.0) | 27 (33.8) | 4.93 | 0.026* |
| Recurrence | 1 (2.0) | 1 (1.3) | 0.00 | 1.000 |
*P < 0.05
Patient-reported outcomes
As shown in Table 4, before surgery, the VAS and ODI scores between the two groups did not show any differences. After surgery, both groups demonstrated significant improvements in pain relief and functional disability. At one-year follow-up, both VAS-back and VAS-leg scores showed further decrease in either group. At the final follow-up, with an average of 22.2 ± 5.8 months for the IELD group and 23.6 ± 6.7 months for the TELD group (Fig. 7), both groups achieved high rates of excellent/good rate as assessed by the modified MacNab criteria, with 92.0% in the IELD group and 91.3% in the TELD group (P = 0.816). However, there was no significant statistical difference in PROs between high and very high-grade migration at any visit in either group (P > 0.05).
Table 4.
Comparison of patient-reported outcomes between IELD and TELD groups
| Variables | IELD group (n = 50) | TELD group (n = 80) | t or χ² value | P-value |
|---|---|---|---|---|
| VAS for back pain | ||||
| Perioperative | 6.9 ± 0.7 | 6.8 ± 0.8 | 0.40 | 0.687 |
| Postoperative 1st day | 3.3 ± 0.5# | 3.2 ± 0.5# | 1.40 | 0.164 |
| 3 months follow-up | 2.5 ± 0.7# | 2.8 ± 0.8# | -1.81 | 0.073 |
| 6 months follow-up | 1.4 ± 0.6# | 1.4 ± 0.7# | 0.34 | 0.732 |
| 12 months follow-up | 1.0 ± 0.6# | 1.2 ± 0.7# | -1.94 | 0.054 |
| Final follow-up | 1.3 ± 1.0# | 1.4 ± 0.9# | -0.51 | 0.614 |
| VAS for leg pain | ||||
| Perioperative | 7.9 ± 1.0 | 8.0 ± 1.0 | -0.46 | 0.648 |
| Postoperative 1st day | 3.3 ± 1.0# | 3.1 ± 0.9# | 0.71 | 0.479 |
| 3 months follow-up | 2.8 ± 0.7# | 3.0 ± 0.7# | -1.76 | 0.082 |
| 6 months follow-up | 1.2 ± 0.5# | 1.1 ± 0.7# | 0.86 | 0.389 |
| 12 months follow-up | 0.9 ± 0.5# | 1.0 ± 0.5# | -1.12 | 0.265 |
| Final follow-up | 1.4 ± 1.0# | 1.2 ± 0.8# | 1.39 | 0.169 |
| ODI (%) | ||||
| Perioperative | 52.6 ± 5.5 | 53.2 ± 6.0 | -0.62 | 0.533 |
| Postoperative 1st day | 21.4 ± 5.2# | 19.8 ± 5.5# | 1.70 | 0.091 |
| 3 months follow-up | 13.9 ± 3.7# | 14.0 ± 3.8# | -0.15 | 0.882 |
| 6 months follow-up | 11.0 ± 3.6# | 11.4 ± 4.0# | -0.57 | 0.571 |
| 12 months follow-up | 10.9 ± 3.7# | 10.8 ± 3.7# | 0.22 | 0.824 |
| Final follow-up | 7.3 ± 4.8# | 7.3 ± 4.5# | -0.02 | 0.988 |
| Modified MacNab evaluation, n (%) | 0.03 | 0.816 | ||
| Excellent | 42 (84.0%) | 66 (82.5%) | ||
| Good | 4 (8.0%) | 7 (8.8%) | ||
| Fair | 3 (6.0%) | 6 (7.5%) | ||
| Poor | 1 (2.0%) | 1 (1.2%) | ||
| Excellent/good rate (%) | 92.0% | 91.3% |
Abbreviations: VAS Visual analog scale, ODI Oswestry Disability Index
#Compared with preoperative, the difference was significant (P < 0.05)
Fig. 7.
VAS and ODI outcomes of IELD and TELD. A Changes in VAS for back pain over time. B Changes in VAS for leg pain over time. C Changes in ODI over time. Abbreviations: VAS, visual analogue scale, ODI, Oswestry disability index
Radiological results
There were no statistically significant differences between the two groups in terms of APDID (43.5 ± 4.2 mm vs. 43.4 ± 3.4, P = 0.960) or DSCA (124.2 ± 44.3mm2 vs. 124.5 ± 33.8mm2, P = 0.962) on axial lumbar MRI preoperatively (Table 2). At 12 months postoperatively, the APDID significantly decreased to 37.3 ± 5.8 mm in the ILED group and 37.7 ± 3.0 mm in the TELD group (P = 0.647), with no significant difference in the reduction rate between the two groups (14.8 ± 11.3% vs. 13.2 ± 3.9%, P = 0.228). Meanwhile, DSCA significantly increased to 177.7 ± 51.7 mm² in the ILED group and 174.3 ± 38.9 mm² in the TELD group, with no significant difference in the improvement rate between the two groups (52.4 ± 46.3% vs. 44.1 ± 24.3%, P = 0.181).
Complications
Table 3 lists complications in the two groups, there were no significant differences in complication rates between two groups. In the IELD group, one case of dural tear required tight suturing of the deep fascia and prolonged bed rest, which was managed successfully, with no further events during follow-up. In the TELD group, one patient experienced nerve root irritation, which was successfully treated with two days of intravenous administration with dexamethasone. There were also facet joint injuries in one patient from the IELD group and two from the TELD group, all of which resolved with conservative treatment and bed rest. No early wound infection or neurological dificit were observed in either group after surgery. Each group had one patient with recurrence at the index segment, but without nucleus pulposus migration. The patient in IELD group underwent transforaminal lumbar interbody fusion, while the patient in TELD received microdiscectomy. Notably, slightly more patients in the TELD group complained of residual back pain during the follow-up (16.0% vs. 33.8%, P = 0.026). Additionally, there was no significant difference in in complication rates between patients with high versus very high-grade migration within either group (P > 0.05). Moreover, we conducted a regression analysis on factors that may contribute to postoperative residual back pain. The results indicated that prolonged operation time and intraoperative facet joint injury may be independent risk factors for postoperative residual back pain (Table 5).
Table 5.
Logistic regression analysis of residual back pain in HM-LDH patients
| Variables | OR | 95%Cl | P-value |
|---|---|---|---|
| Age | 1.005 | 0.970–1.042 | 0.770 |
| Gender | 0.387 | 0.134–1.116 | 0.079 |
| BMI | 1.135 | 0.987–1.306 | 0.076 |
| VAS for back pain | 1.078 | 0.570–2.037 | 0.817 |
| Pfirrmann grade | 1.798 | 0.989–3.269 | 0.054 |
| Migration grade | 0.470 | 0.152–1.458 | 0.191 |
| Operation time | 1.072 | 1.042–1.102 | < 0.001* |
| Facet joint injury | 1.257 | 1.142–1.383 | < 0.001* |
Abbreviations: BMI, body mass index; VAS, visual analog scale
Note: * P < 0.05, statistically significant differences
Discussion
HM-LDH is a more severe type of LDH, characterized by the nucleus pulposus tissue breaking through the annulus fibrosus and posterior longitudinal ligament, and then migrating upward or downward [19]. Due to the anatomical specificity of the L4/5, selection of surgical approach for L4/5 HM-LDH was quite challenging for surgeons [6, 20], especially for full-endoscopic removal of migrated nucleus pulposus. Although TELD was regarded as one of the minimally invasive treatments for LDH, its application in cases of HM-LDH remained limited. Reports indicated that a remnant disc fragment was present in 5%-13% of patients, primarily due to the rather smaller working cannula used in TELD [21, 22]. Lee et al. [23] reported that only 78.9% of patients with HM-LDH achieved excellent or good outcomes based on the MacNab criteria. To overcome this limitation, Choi et al. [22] incorporated foraminoplasty to enlarge the foramen, which improved the success rate to 91.4%. However, 5 out of 59 patients required a second procedure, and 3 experienced persistent leg pain due to incomplete removal of the distal fragment and the injury of the exiting nerve root during foraminoplasty. Ying et al. [24] founded that foraminoplasty, performed through the superior border of the inferior pedicle, could reduce the incidence of facet joint injury and damage to the exiting nerve root. Foraminoplasty was often essential for removing the distal part of a migrated nucleus pulposus, which might have been concealed at the inner edge of the pedicle [25, 26]. While foraminoplasty improved success rates, it also carried the risk of complications such as nerve root injury and segmental instability. In contrast, IELD offered notable advantages for treating HM-LDH, including a more direct approach to the distal portion of the migrated fragment, with a reduced risk of exiting nerve root injury [27]. Despite the L4/5 interlaminar space being smaller than that of L5/S1, laminotomy under endoscope with high-speed burr/Kerrison rongeur could facilitate enlarging the interlaminar space as well as the working area.
In our study, the IELD group exhibited less fluoroscopy times and shorter operation time, which was consistent with Zhao et al. [7] and Huang et al. [28]. The interlaminar approach, with its anatomical familiarity resembling open surgery, allows surgeons to access the migrated disc more efficiently. A study by Jamaleddine et al. [29] found that the learning curve for TELD is much steeper compared to the IELD. Additionally, for cases with very high-grade migration, foraminoplasty was inevitably required, which not only increased the fluoroscopic times but also raised the operation difficulty and time. However, the IELD and TELD groups showed comparable intraoperative blood loss and postoperative length of stay, with no statistically significant differences. At our center, IELD and TELD are performed under different anesthesia methods. IELD is typically conducted under general anesthesia. In contrast, TELD is usually performed under local anesthesia combined with intravenous sedation. General anesthesia suppresses intraoperative pain perception but doesn’t eliminate postoperative nociception, with residual anesthetics potentially masking early pain expression [30]. Local anesthesia provides real-time feedback and effective analgesia but may cause more discomfort and higher early postoperative pain if titration is inadequate [31]. While studies [32, 33] suggest similar long-term outcomes with different anesthesia techniques for PELD, the choice should be tailored to the patient’s characteristics and LDH type. On the one hand, for patients with severe preoperative back pain and leg pain, or even sciatic scoliosis, general anesthesia may be more advantageous for preoperative positioning and puncture localization. On the other hand, for elderly patients with multiple comorbidities, local anesthesia may be more appropriate.
Anatomical factors also play a role in selecting the surgical approach, as the previous study reported [20]. In our study, the IELD group exhibited a larger interlaminar window, which provides a safer surgical corridor, requiring less laminotomy and preserving spinal stability [20, 34]. Conversely, in the TELD group, we found the width and area of intervertebral foramen were larger, while the height showed no significant difference compared to the IELD group. A wider intervertebral foramen offers a more spacious corridor, reducing the risk of nerve root compression or injury [35]. The increased area also improves maneuverability during decompression. However, height of intervertebral foramen is less critical, as it is generally sufficient for instrument passage, with intervertebral foramen width being more important for safe navigation and instrument handling [36]. Although the IELD group had a slightly higher proportion of very high-grade migration, the difference was not statistically significant (P = 0.138), consistent with findings by Zhao et al. [7].
Despite these differences, both techniques demonstrated comparable improvements in PROs including VAS, ODI, and MacNab scores, consistent with the findings Zhao et al. [7]. All patients achieved a high rate of satisfaction at the final follow-up (92.0% vs. 91.3%, P = 0.816). Our results show that the APDID significantly decreased and the DSCA significantly increased compared to preoperative values, which is consistent with the findings reported by Li et al. [37]. This suggests that both ILED and TELD can achieve effective decompression outcomes in managing L4/5 HM-LDH. However, in the IELD group, one patient experienced a dural tear during surgery, and one patient had a facet joint injury, which was consistent with Wasinpongwanich et al. [38]. Due to the relatively narrow interlaminar window at L4/5 and the significant distance of some migrated nucleus pulposus, the procedure often necessitates laminotomy to increase access to the herniated disc, which can lead to unintended trauma to surrounding tissues, including the dura and facet structures. In the TELD group, one case of exiting nerve root irritation occurred during surgery, and two cases experienced facet joint injury, which was consistent with Wang et al. [17]. The nerve root irritation likely resulted from the need for advanced foraminoplasty, which can inadvertently compress or irritate the nerve roots, particularly when enlarging the foramen to access the migrated nucleus pulposus [17]. Additionally, each group had one case of recurrence, which is close to the recurrence rate of 4.8% reported by Huang et al. [28]. However, there was no significant statistical difference in the rate of complications between the two groups.
It should be pointed out that, the TELD group had a higher incidence of residual back pain at the final follow-up, which is consistent with Xu et al. [39]. Longer operation time during TELD can increase tissue trauma and inflammation, which may exacerbate postoperative back pain and delay recovery. Partial resection or disturbance of the facet joints during foraminoplasty may affect the local stability of the facet joint and may also stimulate the posteromedial branches of the lumbar spinal nerves, leading to a higher incidence of residual back pain [15, 17]. In addition, TELD often involves more intradiscal manipulation possibly accelerating disc space collapse, which may be strongly associated with residual back pain [17]. Although a part of the lamina also needs to be resected in some IELD surgeries, the degree of destruction to the stability of the lumbar spine is much lower than that in the TELD group.
This study systematically and comprehensively compared the radiological data, preoperative data, PROs and complications of two different approach methods for treating L4/5 HM-LDH. We found that both IELD and TELD can be effective treatment methods, with comparable satisfied outcomes. IELD allows direct visualization for nerve-root decompression with less impact on lumbar spine stability, shorter operation time, less fluoroscopy times, and fewer residual back pain. The interlaminar window and the intervertebral foramen, are likely the factors influencing the selection of surgical approach. Therefore, a comprehensive preoperative evaluation of radiological information, combined with the patient’s physical characteristics, is essential for making the optimal decision. Our results may offer a theoretical basis for the selection of surgical approach in PELD for L4/5 HM-LDH. Considering the steeper learning curve of TELD and the occasional necessity of foraminoplasty to access the migrated nucleus pulposus, we may recommend that beginners prioritize IELD for managing L4/5 HM-LDH. Once sufficient experience is gained and the endoscopic anatomical structures are well understood, TELD can then be considered.
The present study still has several limitations. First, this is a retrospective study with a relatively small sample size, and the selection of surgical approach was basically based on mainstream standards and surgical experience. There may be some bias in the selections of patients and approaches. Second, all measurements of the anatomical parameters in this study were performed on X-rays, which may affect the accuracy of some results. Therefore, a future study based on CT is needed to verify the accuracy of our findings. Third, all surgeries were performed by the same experienced spine surgeon from single-center, which may limit the generalizability of some of the results. Therefore, a large sample size, prospective, multi-center, randomized controlled trial is needed in the future to further validate our results.
Conclusions
For L4/5 HM-LDH, both IELD and TELD can achieve good clinical and radiological outcomes. IELD was superior to TELD regarding operation time, fluoroscopy times, and postoperative residual back pain. However, selection of surgical approach depends on the anatomical structure, migration characteristics, and the operative skills of the surgeon. Rational preoperative planning of the surgical method can maximize the benefits of minimally invasive surgery for patients.
Acknowledgements
Not applicable.
Abbreviations
- IELD
Interlaminar endoscopic lumbar discectomy
- TELD
Transforaminal endoscopic lumbar discectomy
- HM-LDH
Highly migrated lumbar disc herniation
- LDH
Lumbar disc herniation
- PROs
Patient-reported outcomes
- VAS
Visual analogue scale
- ODI
Oswestry Disability Index
- MRI
Magnetic resonance imaging
- CT
Computed tomography
- PACS
Picture archiving and communication system
- APDID
Anteroposterior diameter of the intervertebral disc
- DSCA
Dural sac cross-sectional area
- PELD
Percutaneous endoscopic lumbar discectomy
Authors’ contributions
Shicheng Zheng gathered the data. Shicheng Zheng, Xu Sun, Zongshan Hu and Qinghua Zhao contributed to writing the manuscript. Bin Wang, Zezhang Zhu and Yong Qiu contributed to the experimental design. All authors approved the final version of the manuscript.
Funding
This study was supported by fundings for Clinical Trials from Nanjing Drum Tower Hospital, Affiliated Hospital of Medical School, Nanjing University (2024-LCYJ-MS-04), fundings for New Clinical Technologies from the Affiliated Drum Tower Hospital, Medical School of Nanjing University (XJSFZLX202303), and Jiangsu Provincial Medical Innovation Center of Orthopedic Surgery (CXZX202214).
Data availability
The datasets generated and/or analyzed during the current study are not publicly available due to limitations of ethical approval involving the patient data and anonymity but are available from the corresponding author on reasonable request.
Declarations
Ethics approval and consent to participate
This study was approved by the ethics committee of Nanjing Drum Tower Hospital (2025-0289-01). The study was performed in accordance with the principles of the Helsinki Declaration of 1964 and its later amendments. All patients provided informed consent for participation in the study and research publication.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The datasets generated and/or analyzed during the current study are not publicly available due to limitations of ethical approval involving the patient data and anonymity but are available from the corresponding author on reasonable request.