Introduction

Low back pain is one of the most prevalent conditions in pain clinics. Among the different causes that generate this type of pain, discogenic pain is one of the most common and a true challenge for professionals to treat. The diagnosis of discogenic low back pain is usually made through patient history and physical examination, although the most important diagnostic tool is lumbar magnetic resonance imaging (MRI) that classifies according to modified Pfirrmann grades (1). The definitive diagnosis of the cause of pain can be made through provocative discography. This technique allows visualization of the disc image and also provokes pain in the patient, enabling verification of whether the pain is concordant or not with the patient’s symptoms (2).

Discogenic low back pain has been widely treated using various interventional techniques (3), with variable results. Due to the limited evidence of intradiscal treatments and the potential complications associated with the procedures, treatment through bilateral blockage of the L2 dorsal root ganglion (DRG) becomes of particular interest (3). This technique consists of the administration of a determined volume of local anesthetic (with or without corticoisteroids) to the epidural space through a transforaminal approach at the chosen level, in this case at the exit of the L2 dorsal root ganglion bilaterally.

Studies conducted on rats have shown that the ventral portion of the L5-L6 discs is innervated by neurons located in the L1 and L2 DRGs (4). If these results are extrapolated to humans, it appears that nociceptive information from the L4-L5 and L5-S1 discs has multisegmental innervation. On one hand, it is transmitted through the DRG at its respective level, and on the other hand, by neurons located in the bilateral L2 DRGs (5).

Ohtori et al. reported that bilateral L2 DRG blockage is effective in the treatment of discogenic low back pain, with evidence of changes in cerebral metabolic activity following treatment at this lumbar level (6).

The objective of this article is to describe a new technique for accessing the DRG L2 using a fluoroscopy approach in anteroposterior projection as opposed to the traditional approach (oblique an craniocaudal angulation on one side and then the contralateral side) through the description of a clinical case of a patient with discogenic pain. The patient signed the informed consent form and we received approval for publication by the ethics committee of the Jiménez Díaz Foundation.

Clinical case

A 45-year-old female patient, with no relevant personal history, underwent right L5 hemilaminectomy and partial L5-S1 discectomy. The patient had been experiencing low back pain for several years, with right L5S1 root irradiation, after lumbar epidurolysis, radicular pain improves with persistent continuous low back pain. The pain was continuous and worsened when transitioning from a sitting to standing position, especially in the morning and after prolonged periods of rest. The pain was mechanical and did not present any neuropathic radiation. The pain had worsened in recent months without any identifiable cause, reaching a score of 7 out of 10 on the visual analog scale (VAS), where 0 is no pain and 10 is excruciating pain.

Physical examination revealed a normal pain threshold with preserved mobility. Apophyseal tenderness was observed at the L4-L5-S1 level, but there was no pain upon examining facet lines or lumbar muscle exploration. There was no muscular instability dependent on the multifidus muscles. Neurological examination revealed normal sensitivity and strength, with preserved and symmetrical reflexes and no abnormalities.

A lumbar MRI was performed, which showed changes due to right S1 minimal hemilaminectomy and L5-S1 partial discectomy, discopathy at the L4-L5 and L5-S1 levels, with decreased disc height and diffuse disc bulging. No focal herniations were observed, and there was no clear compromise of the canal, lateral recesses, or neural foramina. There were no other significant pathologies.

Based on the clinical presentation, physical examination, and results of the complementary exams, the clinical diagnosis of discogenic low back pain was established, and due to the absence of radicular symptoms and based on the multisegmental innervation of the lumbar discs, we decided to perfom a diagnostic GRD block at the bilateral L2 level using 1 ml of 0.25% bupivacaine per side. After the procedure, the patient reported relief from pain for 3 weeks (VAS 3/10) compared to her baseline pain. It was considered a positive diagnostic block , and was decided to proceed with radiofrequency treatment at the bilateral dorsal root ganglion.

Technique

With the patient in prone position, L2 was identified using the last dorsal vertebra (T12) as a reference in an anteroposterior projection. To perform this approach, it is important to obtain a perfect anteroposterior view, with the spinous processes in the central part of the image and both pedicles equidistant from it. The double contour of the vertebral body, if present, was eliminated by angling the C-arm cranially or caudally. Once this image was obtained, a line was drawn between both L2 pedicles. The laminae at this level are narrower than the vertebral body, which enables the approach in this projection, unlike other levels (Figure 1). The target site is immediately lateral to the central part of both laminae (Figure 2).

Once the targets have been defined, a radiofrequency needle is placed on each side under tunnel vision (CR10- Radiofrequency cannula no temperature control and a medical port, 10 cm, 23 G. y 5 mm tip) in the same projection (Figure 2). In the lateral projection, the needle is inserted until the tip is located in the foramen (Figure 3), in the posterosuperior quadrant (junction between the upper third and the lower two-thirds), while sensory stimulation is tested and should be positive between 0.2-0.5 V (causing paresthesia in the corresponding L2 territory), and motor stimulation should be double the sensory stimulation to elicit a motor response in the corresponding territory, indicating the correct placement of the tips of both needles. The projection is again adjusted to anteroposterior, and the correct placement of both needles is confirmed using non-ionic radiopaque contrast (Iopamiro® iopamidol 300 mg/ml) while ruling out intravascular or intrathecal needle tip position (Figure 4). Medication is then administered (2 ml of 0.125 % bupivacaine and 6 mg of betamethasone per side), and pulsed radiofrequency is applied at 45V for 4 minutes (Figure 5).

During the follow-up evaluation after the procedure, an improvement in the VAS was observed. The patient had a baseline VAS of 7 out of 10, which decreased to 3 out of 10 with the diagnostic block and further decreased to 2 out of 10 with pulsed radiofrequency. The patient reported improved performance in daily activities, with a Likert scale improvement of 7 points, corresponding to a 75-100% improvement.

Discussion

Discogenic pain caused by degeneration is a common cause of low back pain. The pathophysiological process involves increased intradiscal stresses that result in structural damage and subsequent local inflammatory reactions with the release of proinflammatory cytokines, leading to pain (7).

The initial treatment for discogenic low back pain are conservative measures that include physical and pharmacological therapies. If conservative treatment fails, minimally invasive interventional treatments should be initiated. Surgical intervention should be considered if conservative and interventional treatments are unsuccessful. Several interventional treatments have been described for discogenic pain, including intradiscal techniques using corticosteroids, conventional or pulsed radiofrequency, and platelet-rich plasma, as well as intradiscal techniques using devices like IDET or disctrode (1).

Other successful treatments include applying radiofrequency to the sinuvertebral nerve and the communicating branch (8,9). Despite the availability of these minimally invasive interventional treatments, there is currently insufficient scientific evidence to establish a standard treatment. Bilateral treatment targeting the dorsal root ganglion (DRG) at the L2 level has been the subject of recent study (10). The standard technique described for blocking the L2 DRG involves placing the patient in a prone position, then positioning the C-arm in anteroposterior (AP) view to locate the target and then moved cranially to eliminate the double contour. The fluoroscopy arc is then positioned obliquely ipsilateral (20-30°) to the affected side to locate the “scotty dog” image. The target, located at the junction of the head and neck of the “scotty dog” (6 o’clock position), is marked with a radiopaque marker, and the needle is inserted under tunnel vision. The C-arm is then repositioned in the lateral view, and the needle is advanced to the innermost part of the foramen. Real-time radiopaque contrast is administered in the AP view, which should diffuse into the anterior epidural space.

This new approach using only the AP projection facilitates targeting the L2 DRG in several ways. On one hand, it allows the technique to be performed with a single projection, providing access to both ganglia with the subsequent confirmation in the lateral view. On the other hand, it reduces surgical time and the movements of the C-arm, thereby making it easier to reach the target using a tunnel vision technique.

In the standard approach, using the oblique projection for nerve blocks, and particularly in this bilateral approach involving movement of the C-arm from one side to the other, can make needle placement more challenging and potentially lead to complications for the patient. By successfully performing the technique in the AP projection, the technical difficulty is reduced, as are the associated potential complications.

Anatomically, the GRD increases in size as we descend from L1 to S1, being located in the upper part of the intervertebral foramen, below the pedicle. In the upper lumbar region (L1, L2 and L3) it is located slightly more dorsal and medial, while in the lower lumbar region L4 and L5 the ganglion is located more anteriorly and laterally (11). The more dorsal and medial location at the high lumbar level would facilitate the action of the pulsed radiofrequency field of the needle tip on the L2 ganglion with this approach (Figure 6).

Otherwise, the anatomy of the L2 vertebra, with its narrower mid-lamina region located between the pedicle and the lower facet joint, allows for accessibility to the foramen. Performing this type of treatment using an AP projection facilitates a faster and simpler approach, with caudocranial angulation that keeps the needle tip within the plane of the vertebral body, thus avoiding inadvertent intradiscal puncture. It should be noted that it is not always possible to obtain an optimal image due to the patient’s anatomy, and in cases where it is not possible to achieve an optimal fluoroscopic image of both foramina, it is necessary to resort to the traditional approach to ensure proper access. Although surgical time is not of vital importance for the final outcome in patients, reducing the prone position time is significant for patients with chronic pain, as this position often increases lumbar pain.

Conclusion

In this publication, we describe the technique of approach under anteroposterior vision for a diagnostic block of GDR bilaterally at the L2 level for low back pain of discogenic origin and subsequent radiofrequency treatment through a clinical case. We consider the possibility of this treatment as a therapeutic alternative for patients with discogenic pain, before performing an intradiscal treatment and performing this approach as an option for daily practice, due to its greater technical ease, especially as an alternative for those cases in which the oblique approach is difficult to access. There are several limitations in this study. Firstly, it only describes the experience of a single patient, which may result in a lack of external validity. Secondly, the main limitation is the scarce literature available regarding the exact description of these types of techniques, and specifically the lack of documented cases using the proposed approach. Therefore, we consider it necessary to develop studies with a sufficient number of patients and appropriate design to increase the scientific evidence for this treatment, and specifically for this new proposed approach.

Conflict of interest

There was no funding received for writing this manuscript. David Abejón is a consultant for Boston Scientific, Saluda, Cardiva, Abbott, Grunenthal and Medtronic. Eva M. Monzón is a speaker for Cardiva. Alberto Rios, Víctor Fajardo and Cristina Abad have no conflicts of interests.

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