Pathological Patterns and Technical Considerations in Transforaminal Endoscopic Lumbar Foraminotomy for Fusion-Segment Radicular Pain

Abstract

Purpose

This study aimed to describe the predominant pathological patterns observed intraoperatively, the endoscopic decompression techniques used, and the clinical outcomes of transforaminal endoscopic lumbar foraminotomy (TELF) for fusion-segment radicular pain.

Patients and Methods

This retrospective descriptive case series included 14 consecutive patients who underwent TELF for unilateral radicular pain caused by foraminal pathology within a previously fused lumbar segment. The compressive pathology was assessed preoperatively using magnetic resonance imaging and computed tomography scan. Then, it was confirmed or further characterized intraoperatively via direct endoscopic visualization. Clinical outcomes were evaluated using the visual analog scale (VAS), Oswestry Disability Index (ODI), and modified MacNab criteria during a 12-month follow-up period.

Results

The pathological findings were categorized as perineural adhesion (n = 8, 57.1%), screw-related impingement (n = 4, 28.6%), and foraminal disc herniation (n = 2, 14.3%). The mean VAS score for leg pain decreased from 8.29 ± 0.61 preoperatively to 1.86 ± 1.23 at 12 months postoperatively (p < 0.001). The mean ODI decreased from 71.83% ± 4.79% to 16.89% ± 11.08% (p < 0.001). According to the modified MacNab criteria, 85.7% of the patients achieved excellent or good outcomes. Two patients developed transient postoperative dysesthesia, and one case of incidental dural tear was successfully managed endoscopically. None of the patients required revision fusion or repeat decompression during the 12-month follow-up.

Conclusion

TELF may offer a minimally invasive treatment option for fusion-segment radicular pain while preserving the existing fusion construct. Identifying the predominant compressive pathology may facilitate pathology-oriented endoscopic decompression in appropriately selected patients.

Introduction

Persistent or recurrent radicular pain after lumbar fusion surgery remains a clinical challenge for patients and surgeons. Adjacent segment disease is a widely recognized major cause of postoperative symptoms. However, some patients can develop nerve root compression within the previously fused segment itself. This condition is relatively rare and has gained considerably less attention compared with adjacent segment pathology.^1–6 The management of fusion-segment radicular pain can be challenging. The affected neural foramen is often narrowed by postoperative remodeling processes, including fibrosis, bony overgrowth, and disc space collapse, combined with hardware-related changes. Because these lesions develop in a previously operated segment, revision surgery may involve extensive tissue dissection through scarred planes and, in selected cases, hardware revision or extension of the fusion construct.^7–13 Consequently, surgeons are often reluctant to recommend revision surgery unless symptoms are severe and clearly attributed to a specific pain generator.

Transforaminal endoscopic lumbar foraminotomy (TELF) has emerged as a minimally invasive treatment option for lumbar foraminal pathology, with previous studies reporting favorable clinical outcomes while limiting the disruption of the surrounding anatomical structures.^14–18 After lumbar fusion, endoscopic decompression has been applied in two clinically distinct settings. For foraminal pathology at an adjacent segment, transforaminal or full-endoscopic decompression has been considered as a targeted treatment option without routine extension of the existing fusion construct.^19–21 For foraminal pathology arising within the fused and instrumented segment itself, TELF has been described as a tissue-sparing salvage procedure that permits targeted decompression while preserving the existing instrumentation.^22–24

However, previous studies have primarily focused on surgical feasibility, technical approaches, and clinical outcomes rather than on the spectrum and distribution of the compressive pathologies encountered intraoperatively within fused segments. Radicular pain arising within a fused lumbar segment may involve different mechanisms of exiting nerve root compression, including perineural adhesion or fibrosis, screw-related impingement, and foraminal disc herniation.^23,25–30 These pathological findings may affect intraoperative decision-making without necessarily representing mutually exclusive entities or requiring separate predetermined techniques. Therefore, this study aimed to describe the predominant pathological patterns observed intraoperatively, the endoscopic decompression techniques used, and the clinical outcomes of TELF for fusion-segment radicular pain.

Materials and Methods

Study Design and Patient Selection

This retrospective case series included 14 consecutive patients who underwent TELF for unilateral radicular pain caused by foraminal pathology within a previously fused lumbar segment. All procedures were performed by a single senior surgeon between January 2024 and April 2025. The study protocol was approved by the Institutional Review Board (approval no. KHNMC 2026–04-033), and the requirement for informed consent was waived because of the retrospective nature of the study.

The inclusion criteria for this study were as follows: 1) persistent unilateral radiating leg pain in the distribution of the affected exiting nerve root despite appropriate conservative treatment, including the use of medications and selective nerve root block; 2) concordant foraminal pathology within a previously fused and instrumented lumbar segment confirmed on computed tomography (CT) scan and magnetic resonance imaging (MRI); and 3) availability of clinical follow-up data at 12 months after TELF. Foraminal stenosis was evaluated using MRI and CT scan findings based on previously described radiologic criteria.^31,32 Patients with gross hardware failure requiring structural revision, severe cage migration, active infection, tumors, high-grade spondylolisthesis, symptomatic central canal stenosis requiring open decompression, or predominant axial back pain without concordant radicular symptoms were excluded from the analysis.

Pathological Assessment and Categorization

Preoperative MRI and CT scan findings were used to assess the location and underlying mechanism of foraminal exiting nerve root impingement and to plan the endoscopic approach. During TELF, the presumed compressive pathology was confirmed or further characterized by the operating surgeon via direct endoscopic visualization of the exiting nerve root and surrounding structures. The final pathological assessment was based primarily on the intraoperative endoscopic findings, interpreted in conjunction with the preoperative imaging findings. If more than one pathological finding was present, the lesion considered to be the predominant source of exiting nerve root compression in the endoscopic surgical field was used for categorization.

Surgical Technique

All surgical procedures were conducted using a percutaneous transforaminal endoscopic approach under local anesthesia with conscious sedation. The patients were placed in the prone position on a radiolucent table. The entry point and trajectory were planned on the basis of preoperative CT scan and MRI images, with particular attention to the location of the pedicle screws, rods, fusion mass, and target foramen (Figures 1 and 2).

Figure 1.

Representative case of adhesion-dominant nerve root compression within the fusion segment. (A) Plain radiographic image showing previous L3–S1 fusion. (B) Preoperative magnetic resonance imaging (MRI) revealing left L5–S1 foraminal stenosis (arrows). (C) Intraoperative fluoroscopic images showing the placement of a working sheath at the left L5–S1 foramen. (D) Endoscopic views. The initial view (upper) showed severe fibrotic adhesion causing foraminal stenosis (dashed line). The final view (lower) demonstrated decompression of the exiting nerve root (ENR).

Figure 2.

Representative case of screw-related nerve root impingement within the fusion segment. (A) Plain radiographic image showing previous L5–S1 fusion. (B) Preoperative magnetic resonance imaging (MRI) demonstrating right L5–S1 foraminal stenosis (arrows). (C) Intraoperative fluoroscopic image revealing the placement of a working sheath at the right L5–S1 foramen. (D) Endoscopic views. The initial view (upper) showed foraminal stenosis with hypertrophic ligamentum flavum (LF) and an exposed pedicle screw thread. The final view (lower) demonstrated separation of the exiting nerve root (ENR) from the screw thread (arrow).

A posterolateral transforaminal approach was used to reach the symptomatic foramen. In most cases, a relatively lateral trajectory was selected to bypass the existing instrumentation and safely dock on the outer foraminal zone. An 18-gauge spinal needle was advanced toward the target foraminal area under fluoroscopic guidance. After the guidewire was placed and serial dilation was performed, a bevel-ended working sheath was introduced and positioned such that the opening faced away from the exiting nerve root to minimize neural irritation.

Endoscopic decompression was conducted under continuous visualization. Hypertrophic bone, facet overgrowth, foraminal ligaments, and fibrotic scar tissues were excised using endoscopic burrs, punches, forceps, and radiofrequency probes. In adhesion-dominant cases, cautious adhesiolysis and neural mobilization were performed until the exiting nerve root was released from the surrounding fibrotic tissue (Figure 1). In cases of screw impingement, decompression was directed around the screw-related conflict zone, and the nerve root was separated from the offending structure (Figure 2). If present, focal disc fragments compressing the exiting nerve root were also removed as part of the decompression.

The endpoints of decompression were the circumferential release of the exiting nerve root, the visible restoration of neural mobility, and the absence of residual mechanical compression along the foraminal course. Postoperative CT scan or MRI was selectively performed if residual compression or atypical postoperative symptoms were suspected.

Assessment of Clinical Outcome

Clinical outcomes were evaluated preoperatively and at 6 weeks, 6 months, and 1 year postoperatively. Leg pain was examined using the visual analog scale (VAS), and functional disability was assessed using the Oswestry Disability Index (ODI).³³ Global clinical outcomes at the final follow-up were graded according to the modified MacNab criteria.³⁴ Excellent and good outcomes were considered as successful clinical outcomes. The perioperative variables included operative time, length of hospital stay, complications, reoperation, and postoperative instability. The complications included postoperative dysesthesia, dural tears, infection, neurological deterioration, and any event requiring additional surgery. Segmental instability was assessed via follow-up radiography.

Statistical Analysis

Continuous variables were expressed as mean ± standard deviation, and categorical variables were presented as number and percentage. Changes in the VAS scores and ODI over time were evaluated using the Friedman test. A formal subgroup comparison was not performed among pathology types because of the small sample size and the descriptive purpose of the pathological categorization. A p value of < 0.05 indicated statistically significant differences. Statistical analyses were conducted using the Statistical Package for the Social Sciences software (version 22.0; IBM Corp., Armonk, NY, USA).

Results

Demographic and Perioperative Characteristics

The baseline demographic and perioperative characteristics of the 14 consecutive patients who underwent TELF for unilateral radicular pain caused by foraminal pathology within a previously fused lumbar segment are summarized in Table 1. The mean age of the patients was 68.5 ± 7.1 (range: 60–82) years, and nine (64.3%) patients were women. L5–S1 (42.9%) was the most frequently treated level, followed by L4–L5 (35.7%) and L3–L4 (21.4%). Previous fusion involved a single level in 11 (78.6%) patients and multiple levels in 3 (21.4%). The mean interval between the index lumbar fusion and TELF was 4.41 ± 3.59 years. All procedures were successfully completed using a transforaminal endoscopic approach under local anesthesia with conscious sedation. The mean operative time was 59.39 ± 11.99 min, and the mean length of hospital stay was 1.28 ± 0.47 days. None of the patients required intraoperative conversion to open surgery, hardware removal, or revision fusion. During the 12-month follow-up, no patient exhibited radiographic progression of segmental instability or required subsequent extension of the fusion construct. Representative radiologic and endoscopic findings are presented in Figures 1 and 2.

Table 1.

Baseline Characteristics and Perioperative Data

Participants (n = 14)	Value
Age (yr)	68.5 ± 7.1 (range, 60–82)
Sex	Female 9 (64.3%)
	Male 5 (35.7%)
Treated level	L3–4: 3 (21.4%)
	L4–5: 5 (35.7%)
	L5–S1: 6 (42.9%)
Side	Right: 8 (57.1%)
	Left: 6 (42.9%)
Previous fusion	Single-level 11 (78.6%)
	Multi-level 3 (21.4%)
Interval from fusion to TELF (yr)	4.41 ± 3.59
Operative time (min)	59.39 ± 11.99
Hospital stay (days)	1.28 ± 0.47
Baseline leg pain (VAS)	8.29 ± 0.61
Baseline disability (ODI, %)	71.83 ± 4.79

Notes: Continuous variables are presented as mean ± standard deviation (SD), with ranges where provided, and categorical variables as n (%).

Abbreviations: TELF, transforaminal endoscopic lumbar foraminotomy; ODI, Oswestry Disability Index; VAS, visual analog scale.

Clinical Outcomes

All patients had available clinical follow-up data at 12 months. The clinical outcomes improved significantly after surgery. The mean VAS score for leg pain decreased from 8.29 ± 0.61 preoperatively to 4.14 ± 2.07 at 6 weeks, 3.21 ± 1.48 at 6 months, and 1.86 ± 1.23 at 12 months postoperatively (p < 0.001). Similarly, the mean ODI improved from 71.83% ± 4.79% preoperatively to 30.86% ± 19.37% at 6 weeks, 24.82% ± 18.72% at 6 months, and 16.89% ± 11.08% at 12 months (p < 0.001). Based on the modified MacNab criteria, 4 patients (28.6%) achieved excellent outcomes and 8 patients (57.1%) achieved good outcomes at the final follow-up, whereas 2 patients (14.3%) had fair outcomes and none had poor outcomes. Consequently, 12 of the 14 patients (85.7%) achieved successful clinical outcomes, defined as excellent or good results. Table 2 depicts the detailed longitudinal outcome data, and Table 3 shows the global clinical outcomes and postoperative complications. Supplementary Table 1 presents the individual patient trajectories for the VAS score for leg pain and ODI across all assessment points.

Table 2.

Longitudinal Clinical Outcomes

Variable	Preoperative	6 weeks	6 months	12 months	p-value
VAS (leg pain)	8.29 ± 0.61	4.14 ± 2.07	3.21 ± 1.48	1.86 ± 1.23	< 0.001
ODI (%)	71.83 ± 4.79	30.86 ± 19.37	24.82 ± 18.72	16.89 ± 11.08	< 0.001

Note: Data are presented as mean ± SD. P values were calculated using the Friedman test.

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

Table 3.

Modified MacNab Outcomes and Postoperative Complications

Variable	n (%)
Excellent	4 (28.6%)
Good	8 (57.1%)
Fair	2 (14.3%)
Poor	0 (0%)
Successful outcome (Excellent + Good)	12 (85.7%)
Dysesthesia	2 (14.3%)
Dural tear	1 (7.1%)

Pathological Characteristics

According to the predominant compressive pathology, the intraoperative endoscopic findings were descriptively categorized as perineural adhesion or fibrosis, screw-related impingement, or foraminal disc herniation (Figure 3). Table 4 shows the distribution of these findings. Perineural adhesion or fibrosis was the most frequent pattern observed in eight patients (57.1%), and was characterized by dense fibrotic tissues or scar adhesion surrounding or tethering the exiting nerve root, occasionally accompanied by hypertrophic bony overgrowth contributing to foraminal narrowing.^23–26 Screw-related impingement was observed in four (28.6%) patients and was characterized by direct mechanical conflict between the exiting nerve root and a prominent or exposed pedicle screw within the foraminal corridor.^29,30 Foraminal disc herniation was observed in two (14.3%) patients and was characterized by focal compression of the exiting nerve root by residual, recurrent, or newly developed disc material within the fused segment.^27,28

Figure 3.

Pathological patterns of foraminal nerve root compression within the fusion segment. (A) Perineural adhesion (arrows) with dense fibrotic tissues surrounding the exiting nerve root. (B) Screw-related impingement (arrows) caused by pedicle screw prominence. (C) Foraminal disc herniation (arrows) causing focal compression of the exiting nerve root within the fusion segment.

Table 4.

Distribution of Pathological Findings

Pathological Finding	n (%)
Perineural adhesion	8 (57.1%)
Screw-related impingement	4 (28.6%)
Foraminal disc herniation	2 (14.3%)
Total	14 (100%)

Complications

Postoperative complications were infrequent. Two patients (14.3%) developed transient postoperative dysesthesia, which resolved with conservative treatment during the 12-month follow-up. One patient (7.1%) with severe perineural adhesion experienced an incidental dural tear during adhesiolysis. The defect was successfully managed by intraoperative endoscopic sealing, and the patient recovered without cerebrospinal fluid leakage, neurological deterioration, or the need for additional surgery. Deep wound infection, postoperative motor deficit, hardware failure, symptomatic instability, revision fusion, or repeat decompression was not observed during the 12-month follow-up.

Discussion

Clinical Implication of TELF in Fusion-Segment Radicular Pain

Revision surgery after lumbar fusion is often more demanding than primary decompression because of dense epidural scarring, altered anatomy, existing instrumentation, and obscured tissue planes.^7–13 Consequently, some patients undergo extensive revision procedures, including hardware removal and extension of fusion, despite having a focal compressive lesion confined to the neural foramen. This discrepancy between the localized pain generator and the magnitude of revision surgery emphasizes the need for less invasive alternatives.

TELF provides a direct transforaminal corridor to the exiting nerve root while avoiding the posterior scar tissue and previously instrumented surgical field. This approach is particularly suitable for patients with unilateral radicular symptoms, imaging-confirmed foraminal compression, and no evidence of gross instability or hardware failure requiring reconstructive surgery. Previous studies have revealed the efficacy of TELF for lumbar foraminal stenosis and post-fusion foraminal lesions.^14–24 Our findings further support this concept by showing that targeted endoscopic decompression can provide clinically significant improvement in carefully selected patients with pathology confined to the fused segment while preserving the existing fusion construct. The observed improvements exceeded established thresholds for clinically meaningful improvement in pain and disability.^35–37 Although this study was limited by its retrospective design and the absence of a control group, the findings support the application of TELF as a practical tissue-sparing salvage option for appropriately selected patients with fusion-segment foraminal nerve root compression causing radicular pain.

Pathological Spectrum of Foraminal Nerve Root Compression Causing Radicular Pain Within the Fusion Segment

An important finding of the present study is that fusion-segment foraminal nerve root compression causing radicular pain should not be regarded as a single pathological entity. Instead, the intraoperative findings were descriptively grouped according to the predominant compressive pathology as perineural adhesion, screw-related impingement, or foraminal disc herniation. Perineural adhesion or fibrosis was the predominant finding, accounting for 57.1% of cases, followed by screw-related impingement (28.6%) and foraminal disc herniation (14.3%). This descriptive grouping provides a practical framework for understanding the underlying mechanisms of neural compression and considering the corresponding endoscopic decompression maneuvers.

In adhesion-dominant cases, the exiting nerve root is often surrounded by dense scar tissues and tethered within a narrowed foramen. Accordingly, surgical treatment should focus not only on enlarging the bony corridor but also on the circumferential release of the nerve root from the surrounding fibrotic tissue. This pathological process is likely related to chronic postoperative remodeling, foraminal collapse, facet or pedicular overgrowth, and progressive perineural fibrosis.^23–26

Screw-related impingement represents a different mechanism of neural compression. The exiting nerve root may be irritated by screw prominence, malposition, or relative screw exposure following disc space collapse or loss of foraminal height.^29,30 In these cases, the primary surgical target is the conflict zone between the nerve root and the implant. When gross instability or significant hardware failure is absent, endoscopic decompression and neural release may provide effective symptom relief without removal of the existing instrumentation.

Foraminal disc herniation was the least common pathological finding in our series. Nevertheless, it was retained as a separate descriptive category because it represents a discrete compressive lesion rather than a fibrotic or implant-related mechanism. Although solid fusion reduces segmental motion, disc herniation may still occur because of residual disc material, incomplete fusion, local micromotion, or progressive structural changes. Previous reports have likewise described this pathology as an uncommon but clinically important cause of fusion-segment radicular pain.^27,28

Pathology-Oriented Endoscopic Decompression Strategy

TELF within a fused segment is technically more challenging than conventional endoscopic foraminotomy. This is because the working space is narrow, anatomical landmarks may be distorted, and the surgical trajectory can be constrained by pedicle screws, rods, and the fusion mass. Accordingly, a successful surgery is dependent on not only meticulous preoperative planning but also the selection of a decompression strategy tailored to the underlying pathology.

A fundamental technical principle is to establish a safe transforaminal working corridor while minimizing irritation of the exiting nerve root. The working sheath may be positioned in the outer foraminal zone, with decompression performed under continuous endoscopic visualization. In most cases, adequate bony decompression is required before neural manipulation. Hypertrophic bone, facet overgrowth, foraminal ligaments, and fibrotic scar tissues should be removed sequentially to create a sufficient working space, after which adhesiolysis and neural mobilization can be performed safely.

In adhesion-dominant pathology, the primary objective is circumferential (360°) decompression of the exiting nerve root. Hypertrophic bone, foraminal ligaments, and dense fibrotic tissues surrounding the nerve root were meticulously resected to achieve complete neural release. Simply enlarging the bony foramen is often insufficient because persistent perineural tethering may remain despite adequate bony decompression. Therefore, decompression was continued until the exiting nerve root was completely mobilized circumferentially without residual fibrotic attachment. The restoration of free neural mobility, rather than the amount of bone removal, was used as the operative endpoint in these cases.

In screw-related impingement, the key operative objective was to separate the exiting nerve root from the exposed screw thread while preserving the existing instrumentation whenever feasible, rather than performing routine screw removal. Decompression was performed to create a safe margin between the nerve root and the implant. If necessary, limited smoothing of the exposed screw thread may reduce mechanical irritation. The placement of a protective barrier, such as a fibrin sealant patch and an absorbable gelatin sponge, may be considered if persistent contact between the nerve root and the implant is anticipated.

In the two cases of foraminal disc herniation, the operative goal was complete removal of the offending disc fragment and release of the exiting nerve root. Adequate disc decompression facilitates complete neural release and minimizes persistent mechanical compression of the exiting nerve root.

Across the three pathological patterns, TELF was directed toward complete neural release while preserving the existing fusion construct. In this series, decompression was considered complete when free neural mobility was restored and no residual mechanical compression was visible along the foraminal course.^38–40 These technical considerations reflect the operative experience of the authors in a small descriptive cohort and should not be interpreted as evidence-based recommendations. Their safety, reproducibility, and comparative efficacy must be evaluated in larger studies.

Study Limitations

This study has several limitations. First, it was a retrospective case series conducted at a single institution with a relatively small sample size. However, fusion-segment foraminal nerve root compression causing radicular pain is an uncommon condition, and the present cohort represents a highly selected group of patients who underwent TELF. Second, the follow-up period was limited to 1 year; therefore, longer-term studies are needed to determine the durability of symptom relief and the risk of late instability or recurrent foraminal stenosis. Third, the absence of a control group precludes direct comparison with open revision surgery or continued nonoperative treatment. Finally, although three pathological patterns were identified, the small number of patients in each category precluded meaningful subgroup analysis. Accordingly, these pathological groupings should be regarded as descriptive observations rather than a validated classification or a basis for comparative outcome analysis. Future multicenter studies with larger cohorts may help validate these findings and further clarify the role of pathology-oriented TELF in fusion-segment radicular pain.

Conclusion

TELF may offer a minimally invasive treatment option for fusion-segment radicular pain while preserving the existing fusion construct. The identification of the predominant compressive pathology may facilitate pathology-oriented endoscopic decompression in appropriately selected patients.

Funding Statement

This work was supported by a grant from Kyung Hee University in 2026 (KHU-20262306).

Abbreviations

TELF, transforaminal endoscopic lumbar foraminotomy; CT, computed tomography; MRI, magnetic resonance imaging; VAS, visual analog scale; ODI, Oswestry Disability Index.

Data Sharing Statement

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Ethics Approval and Informed Consent

The study was conducted in accordance with the principles of the Declaration of Helsinki. The study was approved by the Institutional Review Board of Kyung Hee University Hospital at Gangdong (KHNMC 2026-04-033). The requirement for informed consent was waived because of the retrospective nature of the study. Patient data confidentiality was maintained throughout the study, and all data were de-identified before analysis.

Author Contributions

All authors made a significant contribution to the work reported, whether in the conception, study design, execution, data acquisition, analysis, and interpretation, or in all these areas; took part in drafting, revising, or critically reviewing the article; gave final approval of the version to be published; agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work. H.A. and Y.A. conceived and designed the study. H.A., Y.A., and B.N. contributed to study methodology, data collection, data analysis, and interpretation. H.A. drafted the manuscript. H.A. and Y.A. critically revised the manuscript. Y.A. supervised the study. All authors read and approved the final manuscript.

Disclosure

Dr Hajin An reports Support for the manuscript from KHU-20262306, during the conduct of the study. Prof. Dr. Yong Ahn reports Support for the manuscript from Kyung Hee University, during the conduct of the study. The authors declare that they have no competing interests.