Introduction

Cervical radicular pain is defined as radiating pain perceived in the upper extremity, caused by irritation or compression of a cervical nerve, its roots, or both(1,2). The C7 nerve root, followed by C6, are the two most commonly affected roots(3). The most common causes include cervical disc herniation and foraminal stenosis. Most epidemiological studies report an annual prevalence ranging from 15% to 50%, with one systematic review reporting an average rate of 37.2%(4). An epidemiological survey of cervical radiculopathy in Rochester, Minnesota, 1976-90, determined the mean age ± SD to be 47.6 ± 13.1 years for men and 48.2 ± 13.8 years for women.(5)

Conservative treatment of cervical radiculopathy includes analgesic and anti-inflammatory medications, immobilization, and physical therapy, and in cases of acute or subacute pain, cervical epidural steroid injections (CESI) are added (6,7). These CESI have been described using an interlaminar or transforaminal approach; however, the evidence for cervical transforaminal approaches is lacking, and complications with transforaminal CESI occur more frequently and can be fatal(8). In cases of chronic cervical radicular pain, or in cases with poor response to previous therapy, the use of pulsed radiofrequency (PRF) to the cervical dorsal root ganglion (CDRG) is indicated.(9)

The anatomical complexity of the cervical spine and the vascular structures in the cervical intervertebral foramen have limited transforaminal approaches. The vertebral artery is implicated in many reported complications, as embolization within this vascular structure can cause impaired blood flow to the brainstem and cerebellum; therefore, we will now provide a brief anatomical overview.

Anatomy of cervical foramen

The transverse processes form part of the transverse foramen, which is present on both sides of the cervical vertebrae. The boundaries of the transverse foramen are defined by four structures: the pedicle, the anterior root of the transverse process, the posterior root of the transverse process, and the intertubercular lamina. The intervertebral foramina in the cervical region are located between the inferior and superior vertebral notches of the adjacent cervical vertebrae.(10)

The cervical foramina are considered neural canals and are oval in shape, each with an average height of 8.1 mm and an average width of 5.6 mm. However, the foraminal height increases from C3/4 to C7/T1 from 7.4 to 8.6 mm, along with the width from C3/4 to C7/T1 from 4.5 to 7.0 mm (11). Nevertheless, Taitz et al. (1978)(12) found different shapes of intervertebral foramina, which they classified into five types. G D, J R, Chandrupatla M, et al. in 2024(13) studied 150 specimens and found that circular shapes are the most common, accounting for 76%. Oval shapes, with both longitudinal axes perpendicular (AP) and tangential (T) to the main axis, are present in 21% of the samples; narrow circular shapes represent a smaller proportion (3%), while irregular shapes are reported infrequently in a single case. With regard to diameters, Molinet G.M. et al. in 2017 studied 121 cervical vertebrae, all of which had transverse foramina with a maximum and minimum mean diameter of 5.60 mm and 4.40 mm on the right side, respectively, and 5.92 mm and 5.57 mm on the left side. Another important anatomical variable is the accessory transverse foramen, observed most frequently in the C3-C6 segment, with 23.4% and a greater unilateral presentation with a right-sided predominance.(11)

Vascular anatomy

Remember that the vertebral arteries, originating from the first portion of the subclavian artery, supply blood to the upper portion of the spinal cord, brainstem, cerebellum, and posterior brain. Each artery fuses with its contralateral artery at the pons to form the basilar artery. The vertebral arteries and vertebral veins run inside the transverse foramen accompanied by the sympathetic plexus(14). Variations are mainly associated with the width and course of the vascular elements, which can cause alterations such as vertebrobasilar insufficiency or modify blood flow, due to the close relationship between the diameter of the transverse foramen and the blood flow of the vertebral artery. (15,16)

The vertebral artery (VA) can be subdivided into three segments: V1, V2, and V3 (1). The V1 segment represents the distance from the origin of the vertebral artery in the subclavian artery to its entry into the cervical transverse foramen at the level of C6 or C7. Segment V2 represents the area from the entrance into the transverse foramen to its exit through the C2-3 transverse foramen. Segment V3 represents its path through the C1-2 transverse foramen, after which it turns medial and dorsal through the groove on the upper surface of the C1 vertebral body to perforate the posterior atlanto-occipital membrane and dura mater, and then passes through the foramen magnum into the cranial cavity. The vertebral arteries eventually merge to form the basilar artery on the ventral surface of the medulla oblongata, but before this, each artery gives rise to other branches. These branches merge to form the anterior spinal artery (ASA), which runs through the ventral median fissure of the spinal cord. The anterior longitudinal spinal artery must be reinforced by segmental medullary arteries (radicular arteries) that arise mainly from segment V2 of the vertebral artery, but may also originate from the ascending and deep cervical arteries. Segments V2 and V3 of the AV are particularly prone to significant variability in their course. (17)

Anterior transforaminal approach

The technique for the cervical transforaminal approach was initially described via the anterior route. The patient is placed in the supine position. The C-arm of the fluoroscope is positioned so that the X-rays are parallel to the axis of the intervertebral foramen. This view is obtained by starting from an anteroposterior (AP) projection and then tilting the image intensifier between 25 and 50°, with a slight caudal tilt if necessary to optimize the radiolucency of the foramen. The correct level is identified in this view. The needle entry point is determined by projecting a metal marker onto the caudal and posterior part of the target intervertebral foramen. A needle coaxial to the X-ray beam is inserted in tunnel vision. The goal was for the needle to be projected as a single point on the fluoroscopic image. After reviewing the lateral and other projections (e.g., contralateral oblique), an AP projection is obtained in which the needle can be slowly adjusted until the tip protrudes through the center of the ipsilateral cervical facet joint.(3)

Modifications to the above technique have been published with the aim of making it safer and minimizing the risk of vascular complications. Chen et al. stated that the optimal needle entry angle using the anterior oblique approach is approximately 50° in the supine position. However, the risk of vertebral artery perforation persists even with this angulation. On the other hand, Myong-Hwan Karm et al. proposed the cervical transforaminal approach with a well-exposed superior articular process (SAP), where the target of the needle tip is the ventral edge of the SAP, and concluded that an approach angle of 70° is safer, considering injuries to vascular structures such as the vertebral artery (VA), the internal carotid artery (ICA), and the internal jugular vein (IJV) (20).

Methods

A fluoroscopically guided transforaminal cervical approach via the posterolateral route was performed in 10 patients with radicular pain and unilateral radiculopathy secondary to disc herniation and/or degenerative disc disease. Non-particulate corticosteroids and a local anesthetic (1 ml) were administered, along with pulsed radiofrequency neuromodulation; 55 V, 5 Hz, 10 ms, 42 °C, 5 min, depending on the duration of the condition (subacute or chronic, respectively).

In 100 % of the subjects, satisfactory nerve mapping and satisfactory sensory and motor stimulation were achieved (Table I). The most common complication was bradycardia during the procedure, which may be due to stimulation of the periosteum; this occurred in 20% of cases and resolved spontaneously. No other complications were observed. The approach technique involving cervical transforaminal injection via the posterolateral route is described below.

Modified posterolateral approach technique

As mentioned above, the posterolateral approach is an attractive alternative, as it allows access to the roots without exposing the arteries and their potential complications. For this reason, we present below a technical report on the posterolateral transforaminal approach.

Description of the technique:

Equipment and monitoring: Standard ASA monitoring (NIBP, SpO2, ECG), cardiopulmonary resuscitation equipment, oxygen via nasal prongs, patent intravenous line, sterile drapes, and gloves are required.

Medication: Midazolam 1 mg IV, Sufentanil 10 mcg IV. The patient is placed in the prone position on a radiolucent table, exposing the cervical area, and the C-arm is positioned with the intensifier in the upper portion.

Step 1. The true AP projection of the level to be treated is obtained, for example, C6 in our report. In this case, the intensifier is rotated cephalad between 10 and 15°, with the spinous process equidistant from the pedicles. To identify the caudal to cephalic levels. T1 is the vertebra with transverse processes pointing cephalad and C7 with transverse processes pointing caudally, or counting from top to bottom, C2 corresponds to the vertebra with the odontoid process.

Step 2. Ipsilateral oblique angulation 45°, the upper and lower ipsilateral pedicle of the levels of interest must be identified, the transverse process, the lateral edge of the articular pillar, and the lateral edge of the vertebral body, which should not be mistaken for the articular pillar. A useful guide is to draw a line on the upper and lower pedicle edge and enter that line equidistant from both pedicles (upper and lower). Using a 20 G RF cannula with a 10 mm active tip and a curved tip (a cannula or blunt-tipped needle will increase the safety of the procedure), identify the entry point, which will be below the pedicle and the lateral edge of the articular pillar. Enter in tunnel vision, staying medial to the edge of the articular pillar until contact is made with bone, see Figure 1.

Step 3. Contralateral oblique. Once contact is made with the lateral edge of the pillar, rotate the arc in the contralateral oblique 55° (the true contralateral oblique is achieved when the edges of the ventral and dorsal laminae have the same radiological density), thus identifying the foramen. The components of the foramen must be identified, such as the posterior wall corresponding to the SAP (superior articular process), the upper edge of the inferior pedicle, the lower edge of the superior pedicle, the uncinate process, and the posterior edge of the vertebral body. Advance the curved-tip cannula to the posterior and inferior edge of the foramen; this represents the final needle tip position. It is important not to go beyond the anterior half of the foramen, due to the high probability of puncturing the vertebral artery. See Figure 2.

Step 4. True lateral. Starting from the true AP (spinous process equidistant from the pedicles), the intensifier is rotated 90° to obtain the true lateral view, complemented by a wiggle motion (wig-wag). The objective is to align the articular pillars and align the laminae, so that the cannula can be seen in the posterior portion of the foraminal groove. This step allows us to visualize the depth of the needle; however, in lower cervical levels, it is not possible to achieve a satisfactory lateral view, so a contralateral oblique check is usually sufficient. See Figure 3.

Step 5. The final AP projection is taken. The tip of the needle should be medial to the edge of the joint pillar but lateral to the pedicle. It is in this position that the non-ionic contrast medium, 0.5 to 1 ml, is applied. Satisfactory neurography is observed, defined as that in which the contrast medium enters the canal and exits the foramen. In this technical report, in 100% of cases, contrast administration was performed using digital subtraction angiography (DSA). Once the nerve imaging has been verified without vascular capture, neurostimulation tests are performed. Sensory stimulation at 0.3 V to 1 V, 50 Hz, and motor response at 0.7 V to 2 V, 2 Hz. Once this has been verified, contrast medium and the corresponding therapy (corticosteroid or pulsed radiofrequency neuromodulation) are administered as appropriate. See Figure 4 and 5.

Discussion

The current management of chronic cervical radiculopathy, after pharmacological treatments have failed, is epidural corticosteroid injection, as mentioned above. The interlaminar approach is preferred when radiculopathy is subacute, although in this same context, the transforaminal approach has proven to be superior in clinical terms. In addition, the transforaminal approach allows for pulsed radiofrequency neuromodulation of the spinal nerve in the context of chronic radicular pain. Although the transforaminal approach has demostrate superior clinical outcomes, the anterior approach is often feared due to the vascular structures near the puncture site, such as the AV, ascending cervical artery, and deep cervical artery. Because of this, the transforaminal cervical approach (CTFESI) is no longer used as a first-line method due to possible complications. Bearing in mind that transforaminal corticosteroid injection allows access to the anterior epidural space and also allows pulsed radiofrequency of the DRG, thereby improving outcomes in chronic radiculopathy, some solutions for safe approach have been proposed. One of these is the ultrasound-guided approach, which allows direct visualization of the nerve between the anterior and posterior tubercles. However, drug administration could only be perineural and not transforaminal epidural, making its application erratic. A second option for CTFESI is to increase the angle to 70° via the anterior route instead of the traditional 50° oblique angle. This study showed that the risk is reduced as long as the SAP (superior articular process) is better visualized and the needle is directed towards that point. Tomographic calculation allows for a reduction in AV puncture, however, this risk is not completely eliminated. It is important to mention that the 70° anterior approach presents technical difficulties.

The posterolateral transforaminal approach is challenging, yet it is often safer than anterior approaches. Two technical reports have been published on the posterior cervical transforaminal approach, the first described by Liza Xiao et al.(21), in AP pointing to the pillar waist, by lateral verification and evaluating the position of the cannula just in the foraminal groove. Verification with contrast medium allows visualization of the dispersion of the medium laterally, but limited medially in the AP view, which is not considered satisfactory neurography. An additional problem when entering in the AP is the high probability of not contacting bone and puncturing anterior structures such as the AV or esophagus. However, it is possible to achieve adequate nerve stimulation and, consequently, a successful therapeutic approach. W. P. McRoberts and A. Trescot (22) in a letter to the editor provide a technical report on the alternative transforaminal approach, a technique where entry is via the posterior route. It is important to note that in this report, the approach is performed using a double-needle technique, the second needle being blunt-tipped and at a 30° angle, so that it can be directed towards the foramen, thus avoiding puncture of the AV and important structures. Although it is a feasible and reproducible technique, it presents some technical difficulties, such as lateral verification, which is difficult in low cervical levels and especially complex in patients with thick necks. However, it adds a safety factor.

There is sufficient evidence of the effectiveness of the cervical transforaminal approach in the management of subacute and chronic radicular pain. However, due to the complexity and potential complications of fluoroscopy-guided interventions, it has not become popular due to fears of fatal complications. The posterior transforaminal approach is usually a safe option, but previous descriptions omit some safety points, and technically, there is no reliable guide for measuring depth. Two crucial points in our posterolateral approach are: a) the tunnel vision approach, always seeking to make contact with a bone structure just before advancing laterally (this safety point is designed for almost all interventional procedures for pain). This first point increases the safety of the procedure; b) the second point is the visualization of the entire foramen, which helps to identify the inferior and posterior aspects of the foramen. To visualize the cervical foramen, a craniocaudal angulation is required depending on the level to be approached and a contralateral oblique angulation of 45 to 55°. This angulation allows safe advancement by turning the cannula laterally during advancement and medially to remain in the foramen.

It is important to mention that the purpose of this technical report is focused on successfully achieving nerve imaging and stimulation of the spinal nerve in 100% of cases, as well as reducing the risk of vascular puncture, because if performed correctly, i.e., the needle is stopped at the edge of the SAP and below the foramen, in a 55° contralateral oblique view, the vertebral artery is not reached. This technique is not intended to demonstrate effectiveness, since transforaminal corticosteroid injection and pulsed radiofrequency neuromodulation have evidence in subacute and chronic radicular pain, respectively, although the NRS over time shows a clear decrease in pain at 6 months.

Conclusion

The posterolateral transforaminal cervical approach, using advancement and verification in the contralateral oblique view, is a new, feasible, and safe technique that constitutes an alternative in the management of subacute radicular pain and, as a target, in pulsed radiofrequency neuromodulation in chronic radiculopathy.

Bibliography

1. Van Zundert J, Huntoon M, Patijn J, Lataster A, Mekhail N, van Kleef M; Pain Practice. 4. Cervical radicular pain. Pain Pract. 2010;10(1):1-17. DOI: 10.1111/j.1533-2500.2009.00319.x.

2. Bogduk N. The anatomy and pathophysiology of neck pain. Phys Med Rehabil Clin N Am. 2011;22(3):367-82. DOI: 10.1016/j.pmr.2011.03.008.

3. Peene L, Cohen SP, Brouwer B, James R, Wolff A, Van Boxem K, et al. 2. Cervical radicular pain. Pain Pract. 2023;23(7):800-17. DOI: 10.1111/papr.13252.

4. Cohen SP. Epidemiology, diagnosis, and treatment of neck pain. Mayo Clin Proc. 2015;90(2):284-99. DOI: 10.1016/j.mayocp.2014.09.008.

5. Radhakrishnan K, Litchy WJ, O’Fallon WM, Kurland LT. Epidemiology of cervical radiculopathy. A population-based study from Rochester, Minnesota, 1976 through 1990. Brain. 1994;117(Pt 2):325-35. DOI: 10.1093/brain/117.2.325.

6. Caridi JM, Pumberger M, Hughes AP. Cervical radiculopathy: a review. HSS J. 2011;7(3):265-72. DOI: 10.1007/s11420-011-9218-z.

7. Woods BI, Hilibrand AS. Cervical radiculopathy: Epidemiology, etiology, diagnosis, and treatment. J Spinal Disord Tech. 2015;28(5):E251-9. DOI: 10.1097/BSD.0000000000000284.

8. Manchikanti L, Falco FJ, Diwan S, Hirsch JA, Smith HS. Cervical radicular pain: the role of interlaminar and transforaminal epidural injections. Curr Pain Headache Rep. 2014;18(1):389. DOI: 10.1007/s11916-013-0389-9.

9. Kwak SG, Lee DG, Chang MC. Effectiveness of pulsed radiofrequency treatment on cervical radicular pain: A meta-analysis. Medicine (Baltimore). 2018;97(31):e11761. DOI: 10.1097/MD.0000000000011761.

10. Manchikanti l, Kaye AD, Falco FJE, Hirsch JA. Essentials of Interventional Techniques in Managing Chronic Pain. Springer; 2018.

11. Molinet GM, Robles FP, Roa I. Anatomical variations of the foramen transversarium in cervical vertebrae. Int J Morphol. 2017;35(2):719-22. DOI: 10.4067/S0717-95022017000200053.

12. Taitz C, Nathan H, Arensburg B. Anatomical observations of the foramina transversaria. J Neurol Neurosurg Psychiatry. 1978 Feb;41(2):170-6. DOI: 10.1136/jnnp.41.2.170.

13. G D, J RP, Chandrupatla M, G N K, B H S. Unveiling Morphological Diversity: An Anatomical Investigation of the Foramen Transversarium in the Cervical Vertebrae. Cureus. 2024;16(8):e67143. DOI: 10.7759/cureus.67143.

14. Sanchis-Gimeno JA, Martínez-Soriano F, Aparicio-Bellver L. Degenerative anatomic deformities in the foramen transversarium of cadaveric cervical vertebrae. Osteoporos Int. 2005;16(9):1171-2. DOI: 10.1007/s00198-005-1908-2.

15. Das S, Suri R, Kapur V. Double transverse foramen: An osteological study with clinical implications. Rev Méd Internac. 2005;12(4):311-3.

16. Kaya S, Yilmaz ND, Pusat S, Kural C, Kirik A, Izci Y. Double foramen transversarium variation in ancient Byzantine cervical vertebrae: preliminary report of an anthropological study. Turk Neurosurg. 2011;21(4):534-8.

17. Wang S, Ren WJ, Zheng L, Sun ST, Zhang BH, Chen Y, et al. Anatomical Variations of the Vertebral Artery: Analysis by Three-Dimensional Computed Tomography Angiography in Chinese Population. Orthop Surg. 2021;13(5):1556-62. DOI: 10.1111/os.13047.

18. Yabuki S, Kikuchi S. Positions of dorsal root ganglia in the cervical spine. An anatomic and clinical study. Spine (Phila Pa 1976). 1996;21(13):1513. DOI: 10.1097/00007632-199607010-00004.

19. Chen B, Rispoli L, Stitik TP, Foye PM, Georgy JS. Optimal needle entry angle for cervical transforaminal epidural injections. Pain Physician. 2014;17(2):139-44. DOI: 10.36076/ppj.2014/17/139.

20. Karm MH, Park JY, Kim DH, Cho HS, Lee JY, Kwon K, Suh JH. New Optimal Needle Entry Angle for Cervical Transforaminal Epidural Steroid Injections: A Retrospective Study. Int J Med Sci. 2017;14(4):376-81. DOI: 10.7150/ijms.17112.

21. Xiao L, Li J, Li D, Yan D, Yang J, Wang D, Cheng J. A posterior approach to cervical nerve root block and pulsed radiofrequency treatment for cervical radicular pain: a retrospective study. J Clin Anesth. 2015;27(6):486-91. DOI: 10.1016/j.jclinane.2015.04.007.

22. McRoberts WP, Trescot A, Kapural L, Apostol C, Abdul H. An Alternative to the Transforaminal Cervical Epidural: A Selective Dorsal Epidural. Pain Med. 2018;19(2):406-8. DOI: 10.1093/pm/pnx128.