Abstract
Background A lumbar disc herniation is the primary cause of sciatica, affecting 1% to 5% of the population annually. Epidural corticosteroid injections, whether via the transforaminal or interlaminar route, are an option for patients with refractory sciatica pain. The transforaminal route has the advantage of directly addressing the site of pathology in the anterior epidural space, between the disc herniation and the nerve root.
Purpose To evaluate the efficacy of transforaminal infraneural epidural injections using corticosteroids in the treatment of radiculopathy secondary to acute lumbar disc herniation.
Study Design Descriptive, nonrandomized, retrospective, and uncontrolled single-center study.
Patient Sample Patients with radiculopathy secondary to acute lumbar disc herniation who underwent transforaminal epidural infiltrations between 2022 and 2024 were included.
Main Outcome Measures Efficacy of transforaminal infraneural epidural injections using corticosteroids in the treatment of radiculopathy secondary to acute lumbar disc herniation.
Methods The inclusion criteria were (1) patients with onset of radiculopathy symptoms in the lower limbs less than 12 weeks prior; (2) patients with persistent radiculopathy symptoms in the lower limbs for more than 8 weeks; (3) clinical signs and symptoms of radiculopathy; (4) lumbar spine magnetic resonance imaging showing discopathy compatible with the clinical examination; and (5) minimum age of 18 years. From a technical standpoint, the entire procedure was performed in the operating room with sedation and local anesthesia.
Conclusions Radicular blocks are minimally invasive forms of treatment for radiculopathy refractory to medication-based analgesia due to an acute lumbar disc herniation. Transforaminal blocks offer the advantage of providing analgesia with a smaller amount of corticosteroid and represent a nonsurgical alternative that appears to be effective in treating radiculopathy secondary to acute lumbar disc herniation.
Clinical Relevance This study highlights that infraneural transforaminal epidural steroid injection provides effective analgesia for acute lumbar radiculopathy secondary to disc herniation while using a smaller corticosteroid dose. This approach may help reduce systemic exposure and procedural risks, offering a safer alternative for patients requiring minimally invasive pain management.
Level of Evidence 3.
Introduction
Sciatica pain has been known since antiquity, but it was only in the early 20th century that its correlation with lumbar disc herniation was established. Disc herniation can be defined as a focal displacement not only of the nucleus pulposus but also of the annulus fibrosus or a fragment of the vertebral endplate beyond the margins of the adjacent vertebral bodies.1
The etiology of sciatica pain is multifactorial. From an electrophysiological standpoint, it is equivalent to ectopic action potentials triggered by various stimuli, such as nerve root compression caused by the herniated intervertebral disc or inflammatory cytokines released by the nucleus pulposus.2
Lumbar disc herniation is a common condition in medical offices and clinics, accounting for about two-thirds of the causes of low back pain, and is the leading cause of sciatica, which affects 1% to 5% of the population annually.3 Acute lumbar disc herniation typically has a benign natural course, with spontaneous resorption occurring in 85% of cases, and clinical pharmacological treatment being the primary therapeutic approach.4
Some indications for surgical treatment of acute disc herniation include cauda equina syndrome, severe paresis characterized by a Medical Research Council scale score of less than 3, and failure of clinical treatment to control sciatica pain. Epidural corticosteroid injections, either via the transforaminal or interlaminar route, are an option for patients who are refractory to clinical pharmacological treatment prior to surgical intervention, as they provide better control of the local inflammatory process.5
There are various forms of epidural corticosteroid injections, such as the caudal approach, where the corticosteroid is administered through the sacrococcygeal ligament via the sacral hiatus, requiring a larger amount of medication to reach the anatomical target. The interlaminar approach delivers the corticosteroid directly at the level in question but in the posterior epidural space, which often makes it difficult for the medication to transition to the anterior epidural space due to the presence of epidural ligaments and scar tissue.6 The transforaminal approach, however, has the advantage of directly targeting the site of pathology in the anterior epidural space, between the disc herniation and the nerve root.7
There are various forms of transforaminal approaches to the epidural space, such as the classic “Scotty dog” approach, where access to the foramen is obtained above the exiting nerve root. In this approach, the safety triangle is formed by the superior vertebral pedicle as the superior margin, the lateral border of the vertebral body as the lateral margin, and the exiting nerve root as the hypotenuse and medial margin. Another approach is via the infraneural route, below the exiting nerve root, called Kambin’s triangle approach. Kambin’s triangle is formed medially by the descending nerve root and/or the dural sac, inferiorly by the pedicle of the lower vertebra, and the hypotenuse/lateral margin by the exiting nerve root.8
The present study aims to evaluate the efficacy of infraneural transforaminal epidural injection with corticosteroids in the treatment of radiculopathy secondary to acute lumbar disc herniation.
Methods
This was a descriptive, nonrandomized, retrospective, and uncontrolled single-center study. There was no control group for comparison with another surgical technique. The primary objective of the study was to present a case series of patients who underwent epidural corticosteroid injections and their respective clinical outcomes.
Patients and Setting
Transforaminal epidural injections performed from 2022 to 2024 in patients with radiculopathy secondary to acute lumbar disc herniation were retrospectively evaluated. All procedures were performed by the same neurosurgeon, a specialist in spinal surgery.
The inclusion criteria were (1) onset of radiculopathy symptoms in the lower limbs for less than 12 weeks; (2) persistent radiculopathy symptoms in the lower limbs for more than 8 weeks; (3) clinical signs and symptoms of radiculopathy; (4) lumbar spine magnetic resonance imaging (MRI) showing disc disease consistent with the clinical examination; and (5) minimum age of 18 years.
Exclusion criteria included (1) lumbar canal stenosis and/or neurogenic claudication; (2) adjacent level disease; (3) inflammatory spondyloarthropathies; (4) segmental instability on dynamic x-ray imaging; (5) suspected infectious conditions (such as spondylodiscitis); and (6) radiological findings inconsistent with clinical examination.
Procedures
During the preoperative consultation, the Numeric Pain Rating Scale (NPRS) was applied prospectively at baseline, on the day of the procedure, and during follow-up, along with a thorough physical examination including provocative tests (such as the straight leg raise—Lasègue test). All patients underwent lumbar spine MRI.
From a technical standpoint, the entire procedure was performed in the operating room, with sedation and local anesthesia, as well as monitoring of vital signs. Before positioning the patient, preoperative planning was conducted using the hospital’s imaging system to determine, based on lumbar spine MRI, the distance from the midline where the foraminal needle insertion would be made. The patient was positioned in a horizontal prone position, with a pillow under the chest and feet, so as to maintain an average 30-degree knee semiflexion. After positioning the patient, meticulous asepsis was performed, and sterile drapes were placed.
Initially, guided by fluoroscopy, the location of the iliac crest on the ipsilateral side of the procedure was marked in an absolute anteroposterior view, particularly in procedures directed at the L5 to S1 level, where higher iliac crests may require a more vertical angulation of the needle. Depending on the level, the Ferguson view was adjusted, which consisted of aligning the superior endplate of the lower vertebra at the level into a single line, without a double contour, by means of cranial angulation of the fluoroscope. Additionally, the oblique view was adjusted according to the vertebral rotation angle, especially in patients with degenerative scoliosis. A Kirschner wire was then used to mark the path for the foraminal needle, with the tip of the wire on the midline of the superior endplate of the lower vertebra.
The planned midline distance from the preoperative imaging was then marked with a ruler, followed by local infiltration at the entry point on the skin with 2% lidocaine. Next, a 22-gauge Quincke spinal needle was introduced at the same marked location, following the previously determined direction on the x-ray image, to infiltrate the entire pathway the foraminal needle would travel through the tissues. Finally, the foraminal cannula was introduced at the entry point, and using the Ferguson anteroposterior view that aligns the superior endplate of the lower vertebra into a single line, the foraminal needle was advanced toward the superior articular process of the lower vertebra until bone resistance was felt. At this point, a lateral view was obtained to assess the correct positioning relative to the superior articular process. Once the correct position was confirmed, the cannula tip was moved cranially to enter the foramen, marked by a loss of bone resistance. At this stage, with rotational movements of the bevel, the cannula was advanced toward the pedicle line. To finish, another Ferguson view was taken to confirm the correct positioning, and a corticosteroid (Triamcinolone and Depo-Medrol) was injected (Figure 1).
Fluoroscopy demonstrating the step-by-step technique of transforaminal epidural injection using corticosteroids in lumbar radiculopathy. (a) A Kirschner wire was used to mark the path for the foraminal needle, with the tip of the wire on the midline of the superior endplate of the lower vertebra. (b) The foraminal cannula was introduced at the entry point, and using the Ferguson anteroposterior view that aligns the superior endplate of the lower vertebra into a single line, the foraminal needle was advanced toward the superior articular process of the lower vertebra until bone resistance was felt. (c) At this point, a lateral view was obtained to assess the correct positioning relative to the superior articular process. (d) Once the correct position was confirmed, the cannula tip was moved cranially to enter the foramen, marked by a loss of bone resistance. (e) To finish, another Ferguson view was taken to confirm the correct positioning, and a corticosteroid was injected with a 360-degree rotational movement of the cannula to ensure maximum coverage of the area by the medication.
Follow-up
After hospital discharge, these patients returned to the clinic, where the NPRS was used to follow up on their cases at intervals of 10 days, 3 months, and 6 months. At the end of this follow-up, the Oswestry Disability Index (ODI, Brazilian-Portuguese validated version) was also applied. Patients reported both their current functional status (at 6 months) and retrospectively recalled their functional status before the procedure, providing both a retrospective preoperative score and a postoperative score. A physiotherapy rehabilitation program was prescribed from the time of hospital discharge. A satisfactory clinical outcome was considered for patients who, at the end of 6 months, remained free of radicular pain (100% improvement in pain symptoms).
Data Analysis
The data were exported from the evaluation forms to an Excel spreadsheet. Then, they were transferred to the jamovi software version 2.3, which was used for data analysis and graphical plotting. Descriptive analysis of categorical variables are presented as absolute (n) and relative (%) frequency distributions. Continuous variables are presented as mean ± SD.
Results
A total of 455 lumbar spine injections were performed in the years 2022, 2023, and 2024. After applying the inclusion criteria, 110 patients were identified for inclusion in the study, 11 of whom met exclusion criteria and were thus excluded from the study: 6 patients were excluded because they had lumbar canal stenosis, 2 because of adjacent segment disease, 2 because of segmental instability on dynamic lumbar spine x-ray, and 1 because they presented with associated seronegative spondyloarthritis. Thus, 99 patients were included in the final analysis (Figure 2).
Patient selection flowchart.
The clinical profile of these 99 patients according to segment level, location, and type of lumbar disc herniation is shown in Table 1. Additionally, information regarding the participants’ age and sex prevalence is presented. Specifically, the sample had a mean age of 53.9 ± 17.6 years (range, 20–91 years). Women showed a slight predominance (54.5%; n = 54) over men.
Description of the clinical profile of patients with disc herniation considered eligible for the study (n = 99).
Most lumbar disc herniations occurred at the L5 to S1 (42.4%) and L4 to L5 (36.4%) levels, with a lower incidence at the higher levels, L3 to L4 (10.1%) and L2 to L3 (9.1%). The L1 to L2 and L4 to transitional vertebra (TV) levels were the least affected (1.0% each; Figure 3). Regarding location, posterolateral herniations were predominant, representing 86.9% of cases, followed by foraminal herniations (12.1%) and extraforaminal herniations (1.0%). In terms of herniation type, most were classified as extrusions (75.8%).
Graphical plot representing the relative distribution (%) of the segmental levels of herniations in the included patients (n = 99). Abbreviation: TV, transitional vertebra.
Table 2 and Figure 2 indicate the clinical outcome (positive or negative). The results show that among the 99 patients with disc herniation considered eligible for the study, the vast majority (85.9%) had a positive clinical outcome (patients who, at the end of the 6-month follow-up, remained free of radicular pain, with a score of 0 on the NPRS). Only 14.1% of the patients experienced a negative clinical outcome (they experienced a recurrence of radicular pain during these 6 months of follow-up; Table 2).
Clinical outcome (positive or negative) evaluated in patients with disc herniation considered eligible for the study.
Regarding functional improvement, at baseline, patients presented a mean ODI score of 52.4 ± 12.7, consistent with moderate to severe disability. At the 6-month follow-up, the mean ODI significantly decreased to 14.7 ± 10.5 (P < 0.001), with a mean improvement of 37.7 points. Overall, 88.9% of patients (88/99) migrated to the category of minimal disability, 7.1% (7/99) were in the moderate category, and 4.0% (4/99) remained in the severe category at follow-up (Table 3).
ODI outcomes.
Discussion
Radicular blocks are minimally invasive forms of treatment for radiculopathy refractory to medication-based analgesia due to an acute lumbar disc herniation. Among the different techniques described (interlaminar, transforaminal, and caudal), the efficacy in reducing sciatic pain is well established, with variations in complications, the degree of pain intensity reduction, and the duration of the analgesic effect.9
Transforaminal blocks offer the advantage of an analgesic effect with a smaller amount of corticosteroid, due to the closer proximity of the needle to the compressive focus of the lumbar disc herniation in the anterior epidural space.10 Some described complications of transforaminal blocks include accidental nerve root injuries, corticosteroid injection into the venous plexus, or even direct vascular injury from the foraminal cannula.11 Among the transforaminal techniques, we have the classic subpedicular (“Scotty dog transforaminal approach”) and an infraneural approach through Kambin’s safety triangle. As the subpedicular approach targets the anterior and superolateral portion of the neuroforamen, it is more susceptible to vascular complications.12
However, as the needle tip is directed more caudally, the risk of these complications decreases.12 According to some researchers, this classic “safety triangle” cannot be considered completely safe, as the emerging nerve root, segmental artery, and, in rare cases, even the artery of Adamkiewicz may pass through this triangle at more caudal levels, such as L2 to L4.13 The infraneural approach targets Kambin’s triangle, located at the dorsolateral aspect of the intervertebral disc.14 As an advantage, it presents a lower risk of vascular injury, including injury to the artery of Adamkiewicz, or inadvertent injury to the emerging nerve root.15 On the other hand, it increases the risk of inadvertent injury to the annulus fibrosus of the intervertebral disc and even the possibility of intradiscal administration of the depot corticosteroid.16
In our study, the retrodiscal (infraneural) foraminal infiltration technique was used in patients who were refractory to conservative medication treatment as a way to avoid surgical procedures, even minimally invasive ones. The marked reduction in ODI scores demonstrates that the intervention led to a clinically meaningful improvement in functional status, with the vast majority of patients transitioning to minimal disability by 6 months. With a sample of 99 patients, 85.9% of the patients remained free of radicular pain after 6 months of follow-up and physiotherapy rehabilitation, with no vascular and/or neurological complications observed. When compared to other epidural infiltration techniques, such as interlaminar, in patients with acute radiculopathy refractory to disc herniation, the retrodiscal transforaminal infiltration showed slightly higher success rates. For example, Nunes et al, in a Brazilian study from 2016, followed 124 patients who underwent interlaminar epidural infiltration for 6 months and reported a success rate of 75.9%.17
One of the reasons cited by several authors for a more significant clinical response in transforaminal infiltrations is the fact that the corticosteroid injection is administered directly at the anatomical site of the disc herniation, in the anterior epidural space. Previous studies using the retrodiscal transforaminal technique for refractory acute sciatica show results similar to those in this study, such as the study by Vad et al in 2002, where 25 patients underwent transforaminal infiltration with an average follow-up of 16 months, reporting a success rate of 84%.18
Regarding the patients who did not achieve satisfactory clinical control with foraminal infiltration, 3 out of the 14 patients who underwent the block engaged in high-impact activities, such as horseback riding, shortly after the procedure, resulting in a new acute disc herniation episode at the same level. If these patients had been excluded from the study, the clinical success rate would have been slightly higher, and it can be stated that the 85.9% success rate is likely underestimated.
The objective of our study was to evaluate the functional improvement and control rate of refractory acute radiculopathy due to lumbar disc herniation in patients who underwent retrodiscal transforaminal epidural infiltration. Some limitations of this study include the absence of a comparative technique and/or group; being a single-center study, and being a nonblinded study in which the same physicians who diagnosed acute lumbar disc herniation were the ones performing the procedures.
Conclusion
Radicular blocks are minimally invasive forms of treatment for radiculopathy refractory to medication-based analgesia due to an acute lumbar disc herniation. Transforaminal blocks offer the advantage of an analgesic effect with a smaller amount of corticosteroid when compared to interlaminar blocks and constitute a nonsurgical alternative that appears to be effective in the treatment of radiculopathy secondary to acute lumbar disc herniation.
Footnotes
Funding The authors received no financial support for the research, authorship, and/or publication of this article.
Declaration of Conflicting Interests The authors report no conflicts of interest in this work.
- This manuscript is generously published free of charge by ISASS, the International Society for the Advancement of Spine Surgery. Copyright © 2025 ISASS. To see more or order reprints or permissions, see http://ijssurgery.com.
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