Transforaminal Percutaneous Endoscopic Discectomy for L3/4 and L4/5 Foraminal and Extraforaminal Lumbar Disc Herniation: Clinical Outcomes and Technical Note

Abstract

Study Design

Retrospective cohort study.

Background

Foraminal and extraforaminal disc herniations account for 7 to 12% of lumbar herniated discs. Various surgical methods, including midline approaches with facetectomy and paramedian techniques, involve significant bone removal, risking spinal instability. The percutaneous transforaminal approach for endoscopic access to lateral disc herniations presents several advantages over traditional techniques and may be more suitable for these cases.

Objectives

This article evaluates the clinical outcomes and potential complications associated with the treatment of foraminal and extraforaminal lumbar disc herniations at the L3/4 and L4/5 levels in patients who have undergone transforaminal percutaneous endoscopic lumbar discectomy.

Materials and Methods

Between 2016 and 2020, a total of 32 patients diagnosed with single-level lumbar disc herniation at the L3/4 or L4/5 foraminal or extraforaminal levels, who had not responded to conservative management, underwent transforaminal endoscopic discectomy. Follow-up evaluations were performed on postoperative day 1 and at 2 weeks, 6 weeks, 3 months, and 12 months. Both pre- and postoperative assessments employed the visual analog scale (VAS) and the Oswestry Disability Index (ODI) to quantify pain levels and functional outcomes. Clinical outcomes were assessed according to the MacNab criteria to determine the efficacy of the surgical intervention.

Results

The average age of patients was 52.6 years, with L4/5 (81.3%) and L3/4 (18.7%) being the most affected levels. The median follow-up was 18.2 months (range, 1–44 months). There was a significant reduction in VAS and ODI scores at follow-ups compared to preoperative levels (p < 0.01). All patients with preoperative neurological deficits improved, though six patients (18.7%) experienced transient dysesthesia that resolved in 6 weeks. Per the MacNab criteria, clinical efficacy was excellent in 56.3% of patients, good in 37.5%, and fair in 6.2%.

Conclusion

Transforaminal endoscopic lumbar discectomy is a safe and effective minimally invasive procedure for foraminal and extraforaminal lumbar disc herniations at the L3/4 and L4/5 levels. It preserves spinal stability, minimizes blood loss, reduces postoperative pain, and allows for quicker recovery, presenting a strong alternative for patients needing surgery for these conditions.

Keywords

foraminal lumbar disc herniation - far lateral lumbar disc herniation - transforaminal endoscopic discectomy

Introduction

Foraminal and extraforaminal disc herniations account for 7 to 12% of all lumbar herniated discs.[1] [2] They typically manifest with radicular symptoms attributed to the involvement of the rostral nerve root exiting at the adjacent neural foramen. The posterior root ganglion is commonly affected, leading to more severe symptoms compared to patients with the more prevalent paramedian, intracanalicular disc herniations. Various surgical approaches, such as midline approaches involving partial or complete facetectomy, intramuscular extraforaminal, and paramedian approaches, have been documented.[3] [4] [5] [6] [7] However, these approaches often entail significant bone removal, posing a risk of spinal instability.[8] [9] [10] [11] [12]

The percutaneous transforaminal approach for accessing lateral disc herniations endoscopically presents several theoretical advantages over traditional approaches. These include reduced trauma, clear operative vision, nerve root decompression under direct vision, and complete removal of the herniated disc.[13] [14] Additionally, this approach is associated with reduced postoperative pain and scarring,[15] while eliminating the risk of spinal destabilization due to the absence of bone removal.[16] The use of a working channel allows for the safe removal of contained or extruded disc material under endoscopic visualization using various tools.

This study aims to evaluate the clinical outcomes and complications of treating foraminal and extraforaminal lumbar disc herniations at the L3/4 and L4/5 levels in a series of patients who underwent transforaminal percutaneous endoscopic lumbar discectomy.

Materials and Methods

A total of 32 patients who underwent transforaminal endoscopic lumbar discectomy for a single level of L3/4 or L4/5 levels of foraminal or extraforaminal lumbar disc herniation by a senior spine surgeon at our institution between 2016 and 2020 were enrolled in this study. The surgical technique was performed by using a 6.9-mm working channel endoscope (Richard-Wolf, Knittlingen, Germany). Patient selection criteria included unilateral, single-level lumbar disc herniations lateral to the dura (foraminal or extraforaminal) visualized on magnetic resonance imaging and signs and symptoms consistent with nerve root involvement. Additionally, the patients had to show failure of appropriate conservative therapies. Exclusion criteria comprised multilevel or recurrent disc herniations and evident spinal instability on dynamic lumbar radiography.

Preoperative data, including demographic information, symptom duration, neurological signs, and vertebral levels of herniation, were collected. Intraoperative findings, operative time, blood loss, and length of hospital stay were retrospectively analyzed. Follow-up evaluations were conducted 2 weeks, 6 to 12 weeks, 6 months, and 12 months postoperatively. These assessments utilized neurological examination findings, the visual analog pain scale (VAS), the Oswestry Disability Index (ODI), and the MacNab criteria.[17]

The MacNab criteria categorized patient outcomes as follows:

• Excellent: no pain and no restriction of activity

• Good: occasional back or leg pain interfering with normal work or leisure

• Fair: intermittent pain curtails work or leisure activities but shows improved functional capacity

• Poor: unimproved symptoms, insufficient improvement to allow increased activity or requirement of reoperation at the same level.

Statistical Analysis

The data were summarized using a median with range for continuous variables and frequency with percentage for categorical variables. Changes in patients' VAS scores and ODI scores from preoperation to postoperation were assessed using paired t-tests. A two-tailed p-value of less than 0.05 was considered statistically significant.

Surgical Technique

All patients underwent the surgical procedure under general anesthesia. The patient was positioned prone with hip and knee flexion on the Jackson spinal surgical table, ensuring abdominal freedom to prevent pressure on the inferior vena cava. This positioning widened the intervertebral foramen without causing tension in the lumbar nerve roots.

Fluoroscopic monitoring in true posteroanterior and lateral views was crucial to verify the accurate placement of the instrumentation at each stage. The skin entry point was identified on a line parallel to the intervertebral disc space in the true posteroanterior view and the line between the tip of the spinous process and the dorsal facet in the true lateral view ([Fig. 1]).

Fig. 1 The skin entry point is determined by a line parallel to the intervertebral disc space in a true posteroanterior view and a line between the tip of the spinous process and the dorsal facet in a true lateral view (A). The true posteroanterior view of the L4/5 level should demonstrate the spinous processes centrally aligned between the pedicles and parallel vertebral endplates (B). In a true lateral view, the vertebral endplates should be parallel, and the pedicles should be superimposed (C).

An 18-gauge spinal needle was directed toward the Kambin triangle from the skin entry point under posteroanterior and lateral fluoroscopic guidance. Ideally, on the posteroanterior view, the needle tip should align with the lateral border of the pedicle. On the lateral fluoroscopic view, the needle tip should be positioned at the base of the superior articular process on the superior border of the pedicle. After removing the stylet of the needle, a guidewire was inserted, followed by the introduction of a dilator and then a beveled working sleeve at the base of the superior articular process ([Fig. 2]). This area was chosen for its ample space from the exiting nerve root, providing a safer approach to avoid injury.[18] A caudal approach along the superior facet surface was employed to prevent damage to the exiting nerve root.

Fig. 2 The working sleeve is inserted into the base of the superior articular process. This area is relatively safe from iatrogenic nerve root injury as it provides the widest space from the exiting nerve root (A and B).

Additionally, while advancing the working sleeve, it was simultaneously turned to retract the exiting nerve root posterolaterally, safeguarding it from the working area. Subsequently, an endoscope was introduced to identify and clear anatomical landmarks such as the pedicle, superior articular process, and exiting nerve root using a flexible radiofrequency probe. To further reduce the risk of nerve injury, it is advisable to approach the foramen with a less perpendicular trajectory ([Fig. 3]).

Fig. 3 Case illustration: A 62-year-old female presented with intense radiating left leg pain after twisting her back while attempting to reach for an object. The straight leg raise test produced negative results, while the femoral stretch test yielded positive findings. Magnetic resonance imaging in both sagittal (A) and axial (B) views revealed an extraforaminal disc herniation at the left side of the L4/L5 level (arrow). In the course of the transforaminal percutaneous endoscopic discectomy procedure (C), verification through posteroanterior (D) and lateral (E) C-arm images confirmed the precise advancement of a 6.9-mm working cannula to the base of the superior articular process. Subsequently, the endoscopic view demonstrated the removal of disc fragments located beneath the L4 exiting nerve root, resulting in the visual liberation of the tensioned nerve root (F–H).

In cases of intraforaminal disc herniation, the disc extrusion is typically situated precisely in this anatomical area—below the superior articular process and cranially toward the superior surface of the pedicle. The removal of the intraforaminal disc fragment reveals the posterior longitudinal ligament, traversing nerve root, and epidural fat, which should be unobstructed and pulsating. Once all the disc material had been cleared, the endoscope was withdrawn, and a sterile dressing was applied.

Results

In a total of 32 patients, comprising 18 females and 14 males, with an average age of 52.6 years (range 32–69 years), the predominantly affected levels were L4/5 (81.3%) and L3/4 (18.7%) ([Table 1]). Preoperatively, the average VAS scores for radicular pain, back pain, and ODI were 7.3 (range 5–10), 5.4 (range 2–10), and 55.6 (range 38–84), respectively. Notably, 12 patients (37.5%) presented with associated neurologic deficits, characterized by muscle weakness or sensory deficits in the affected nerve root distribution, with an average symptom duration of 5.3 months. The median follow-up period was 18.2 months (1–44 months). After the intervention, patients exhibited an average VAS of 1.6 (range of 0–4) for radicular pain, a VAS of 1.8 (range 0–5) for back pain, and an average ODI of 9.9 (range 0–40) at the 12-month follow-up ([Table 2]). Statistically significant improvements were observed in VAS and ODI (p < 0.05 for both values) ([Table 3]). The mean operative time and postoperative hospital stay were 50.8 minutes (range 40–90 minutes) and 1.1 days, respectively. Noteworthy, all 12 patients with preoperative neurologic deficits demonstrated neurologic improvement, with recovery times ranging from 1 to 6 months. Postoperatively, 2 patients (6.2%) experienced residual leg pain, while 6 patients (18.7%) developed transient leg dysesthesia in the same dermatomal distribution as the preoperative radicular pain. However, all dysesthesias resolved within a 6-week period. Importantly, no instances of infection, instability, or herniation recurrence were recorded at the last follow-up. The final outcome was excellent in 18 patients (56.3%), good in 12 patients (37.5%), and fair in 2 patients (6.2%) ([Table 4]).

Table 1 Demographic data and surgical data of the patients

Data	Values
Sex  Male  Female	14 (43.7%) 18 (56.3%)
Age (y)	52.6
BMI (kg/m2)	23.9
Duration of symptoms (mo)	5.3
SLRT positive	18 (56.3%)
Neurological deficits	12 (37.5%)
Level of herniation  L3/4  L4/5  L5/S1	6 (18.7%) 26 (81.3%) 0
Operative time (min)	50.8
Duration of postoperative stay (d)	1.1
Mean follow-up period (mo)	18.2
Postoperative dysesthesia	6 (18.7%)

Abbreviations: BMI, body mass index; SLRT, straight leg raise test.

Table 2 Clinical outcomes

Variables	Preop	Postop
		1 d	2 wk	6 wk	3 mo	6 mo	12 mo
Mean VAS score Back Leg	5.4 7.3	0 1.8	2 3.2	2.5 3.4	2.3 2.0	2.2 1.8	1.8 1.6
Mean ODI score	55.6	17.1	22.9	16.6	14.5	9.7	9.9

Abbreviations: ODI, Oswestry Disability Index; VAS, visual analog scale.

Table 3 VAS score and ODI score compared with preoperation

Variables	Mean difference (SD)	95% CI	p-Value
2-week postoperation  VAS-back  VAS-leg  ODI	3.45 (3.07) 4.09 (3.81) 30.73 (23.98)	1.38–5.52 1.53–6.64 14.61–46.84	0.004 0.005 0.002
1-year postoperation  VAS-back  VAS-leg  ODI	3.72 (3.25) 5.54 (3.20) 43.73 (18.24)	1.53–5.91 3.39–.69 31.46–55.98	0.003 0.001 0.000

Abbreviations: CI, confidence interval; ODI, Oswestry Disability Index; SD, standard deviation; VAS, visual analog scale.

Table 4 Clinical efficacy according to MacNab criteria

	Excellent	Good	Fair	Poor
Number (%)	18 (56.3)	12 (37.5)	2 (6.2)	0 (0)

Discussion

Lumbar disc herniation occurring at the foraminal level involves the compression of the nerve root by sequestrated fragments that migrate superiorly within the neural foramen. Diagnosing these lateral protrusions presents a challenge as they are not typically visualized through myelography and are situated beyond the scope of conventional surgical procedures. The presence of lumbar disc herniation beyond the confines of the vertebral canal was initially demonstrated in a cadaver study by Lindblom in 1944.[19] Subsequently, in 1971, MacNab documented unsuccessful attempts to explore the L4/5 level in patients with L4 radicular symptoms caused by the extraforaminal protrusion of the L4/5 disc. In 1974,[17] Abdullah et al[1] first described the clinical phenomenon of lateral lumbar disc herniation, illustrating its manifestation on discography as “extreme lateral” disc herniation below the facet at the same level or laterally adjacent to the intervertebral disc space.

The incidence of foraminal and extraforaminal disc herniation ranges from 7 to 12%.[1] [2] [20] The highest absolute occurrence rate is observed at the L4/5 and L5/S1 levels. Cephalad involvement of L1/2 or L2/3 is uncommon, except as indicated in the study by An et al,[21] which reported an unusually high incidence of 28%. Additionally, foraminal disc herniation tends to occur in older patients, with the highest occurrence in the sixth decade, in contrast to classical paramedian disc herniation, which peaks in the fifth decade.[22]

Foraminal lumbar disc herniation is characterized by the compression of the nerve root at the same level, distinguishing it from the more common posterolateral disc herniation, which affects the nerve root at a lower level. Clinical symptoms arise from the compression of the nerve root ganglion, predominantly impacting a single nerve root and leading to intense pain, motor deficits, and sensory impairments.[22] Conservative treatment, combining steroidal and nonsteroidal anti-inflammatory drugs, can be effective for foraminal disc herniation. However, if medical therapy fails, persistent pain, significant sensory deficit, or progressive motor weakness occurs, and surgical intervention is necessary. Numerous surgical approaches, such as midline approaches involving partial or complete facetectomy, intramuscular extraforaminal, and paramedian approaches, have been documented.[3] [4] [5] [6] [7] These approaches often involve substantial bone removal, posing a risk of spinal instability.[9] [10] [11] [12]

Accessing lateral disc herniations endoscopically through a percutaneous transforaminal approach presents several potential advantages over traditional methods. These advantages include reduced trauma, enhanced visibility during surgery, nerve root decompression under direct vision, and complete removal of the herniated disc.[13] [14] Postoperative pain and scarring are minimized, and there is no risk of spinal destabilization due to the absence of bone removal.[15] [16] Additionally, the use of a working channel allows for the safe removal of contained or extruded disc material under endoscopic visualization. Several studies have examined the outcomes of endoscopic surgery in treating patients with foraminal and extraforaminal lumbar disc herniation. In one study, 45 patients with soft disk herniation at L1/2 and L2/3 underwent percutaneous endoscopic discectomy, resulting in excellent outcomes for 46.7% of patients, good outcomes for 31.1% of patients, fair outcomes for 13.3% of patients, and poor outcomes for 8.9% of patients.[23] The investigators underscored the importance of patient selection in achieving successful surgical outcomes.

A retrospective analysis of minimally invasive endoscopic surgery for far lateral lumbar disc herniation reported the procedure to be safe and efficacious. However, complications included two cases of incidental dural tear without cerebrospinal fluid leakage and one residual sequestered disk that required repeat discectomy.[24] In a recent prospective study, percutaneous endoscopic discectomy, combined with the new foraminal retreat technique, was employed to address lateral or far lateral disc herniations in 22 patients.[25] The study found that, at the last follow-up, 81.8% of the patients experienced excellent or good outcomes. Another prospective study focused on the treatment of foraminal or extraforaminal lumbar disc herniations in 35 patients using percutaneous endoscopic discectomy.[26] Results showed that, at an average follow-up of 18 months, 85.7% of the patients achieved good or excellent outcomes.

This current study evaluated the outcomes of 32 patients with L3/4 or L4/5 foraminal and extraforaminal lumbar disc herniation who underwent transforaminal percutaneous endoscopic surgery. All patients reported satisfactory results, with 56.3% experiencing excellent outcomes, 37.5% having good outcomes, and 6.2% having fair outcomes. The study concluded that the observed satisfactory results were consistent with those reported in previous studies. Notably, no cases of infection, instability, or recurrent herniation were reported at the time of the last follow-up. During the study, it was observed that six patients (18.7%) experienced temporary dysesthesia in the leg, occurring in the same dermatomal distribution as the preoperative shooting radicular pain. This postoperative dysesthesia (POD) is a unique complication associated with percutaneous transforaminal endoscopic discectomy, with a reported incidence of approximately 1 to 6.7% in published case series.[27] The occurrence of POD is attributed to potential injury to the exiting dorsal root ganglion (DRG) during the procedure. The DRG may be compressed or pierced during guidewire or cannula insertion, leading to inadvertent contact or compression of the exiting nerve root due to the lack of direct visual control. To mitigate the risk of exiting nerve root injury, an alternative caudal approach along the superior facet surface has been recommended.[28] Furthermore, the foraminoplasty technique is suggested to prevent manipulation of the cannula in the presence of foraminal stenosis or facet hypertrophy.

This study presents several limitations that must be acknowledged. First, it was conducted with a limited sample size at a single center, and the follow-up duration was relatively brief. Therefore, there is a clear need for further prospective investigations that encompass a larger patient population, multicenter collaboration, and extended follow-up periods to validate these findings. Second, the cohort consisted exclusively of patients with extraforaminal disc herniations at the L3/4 and L4/5 levels, with no inclusion of cases at the L5/S1 level during the study timeframe. This oversight suggests a necessity for additional research to encompass this specific area.

In conclusion, transforaminal endoscopic lumbar discectomy has been demonstrated to be a safe and efficacious minimally invasive intervention for managing both foraminal and extraforaminal lumbar disc herniation at the L3/4 and L4/5 levels. The procedure offers several notable advantages, including the avoidance of spinal destabilization linked to traditional bone removal, reduced intraoperative blood loss, minimal postoperative discomfort, a swift recovery to preoperative activity levels, and a low rate of complications.

Conflict of Interest

None declared.

Ethical Approval

The study was approved by the ethics committee of Lerdsin Hospital.

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Publication History

Article published online:
10 March 2025