Lumbar spinal stenosis affects more than 200,000 adults in the United States yearly, resulting in substantial pain and disability.^[1] Generally, patients experience radiating pain in the lower limbs secondary to narrowed intervertebral foramen. Pain is partially caused by physical compression from degenerative changes and thickening of the ligamentum flavum, zygapophysial joint, and surrounding soft tissues; however, no unifying theory explains the exact etiology of the pain in lumbar spinal stenosis.^[1] Theories include inflammatory changes around nerve roots, venous congestion, and hematogenous disability.

“Given the high risk of complications, selecting the safest technique for performing a transforaminal ESI is important.”

One of the mainstays of interventional treatment is an epidural steroid injection (ESI). Steroids interrupt the synthesis of prostaglandins, block conduction of nociceptive fibers, and decrease edema around the nerve root, thereby potentially decreasing pain.^[2] ESIs use two common approaches: midline interlaminar and transforaminal. The transforaminal approach has shown excellent clinical efficacy, with improved pain scores, improved ability to complete activities of daily living, and decreased pain-related anxiety and depression.^[2–3] The transforaminal method is often preferred because the injection can be directed toward the more relevant side and nerve root to maximize localized drug concentration.^[4] Comparative studies have shown that transforaminal ESIs are either equal or superior to midline interlaminar ESIs in efficacy and that they are effective in reducing pain, restoring function, and avoiding surgery in a substantial proportion of patients with lumbar radicular pain.^[5] This article compares and contrasts the merits and flaws of the two approaches in technique for transforaminal ESI: the safe triangle method and Kambin’s triangle method.

The transforaminal approach, although proven to have better clinical efficacy, has the potential for significant complications, including air emboli, cerebral thrombosis, epidural hematoma, nerve root injury, vascular transection, and vasospasm. However, the most devastating complications are cord ischemia or vascular injury from needle trauma or intravascular injection of particulate matter.^[3] The spinal cord’s blood supply is complex, with large arteries such as the artery of Adamkiewicz originating between T8–L1 and smaller segmental arteries, which increases the potential risk of vascular damage or ischemia during procedures. Given the high risk of complications, selecting the safest technique for performing a transforaminal ESI is important.

Safe Triangle Technique

The most commonly used technique is the safe triangle or supraneural/subpedicular approach, performed under fluoroscopy. First, the classic Scottie dog view is obtained; then the needle is directed through the skin toward the inferior lateral boundary of the pedicle. The needle is advanced in the lateral view until the needle enters the superior/posterior aspect of the foramen. This approach is generally safe and avoids many dangerous areas such as the radiculomedullary artery. However, it has been associated with reports of devastating neurologic and ischemic complications.^[4]

Figure 1: Schematic image of Kambin’s triangle. The base is the caudad vertebral body, the height is the traversing nerve root, and the hypotenuse is the exiting nerve.

Adapted with permission from Park JW, Nam HS, Cho SK, Jung HJ, Lee BJ, Park Y. Kambin's triangle approach of lumbar transforaminal epidural injection with spinal stenosis. Ann Rehabil Med. 2011;35(6):833–843. https://doi.org/10.5535/arm.2011.35.6.833

Kambin's Triangle Approach

Another technique, based on a critical reanalysis of the anatomy of the neuroforamen, is an approach termed Kambin’s triangle, which is thought to be safer than the “safe triangle” technique.^[4] The landmark is described as a right triangle over the dorsolateral disc. The exiting nerve root forms the hypotenuse of the triangle, the superior border of the caudad vertebral body forms the base or width of the triangle, and the dura/transversing nerve root forms the height (Figure 1).^[6]

To reach Kambin’s Triangle, the fluoroscopic image is created in the oblique view, which aligns the superior articulate process (SAP) in the center of the intervertebral disc, then the needle is advanced in a lateral, inferior direction to the SAP. When the needle contacts the SAP, the direction of the needle is changed to the lateral aspect of the bony landmark. Needle advancement and final placement are confirmed with a lateral view and contrast imaging (Figure 2).

Figure 2: Kambin’s triangle approach of l4 nerve root under fluoroscopy. 2A: Oblique view, where the needle is advanced past the superior articular process (SAP). 2B: Anteroposterior view, which demonstrates the tip in the interpedicular line. 2C: Lateral view used to advance past the SAP to minimize risk of penetration until the needle is at the posterior, inferior aspect of the interverterbral foramen. 2D: Contrast is injected to confirm epidural spread.

Adapted with permission from Park JW, Nam HS, Cho SK, Jung HJ, Lee BJ, Park Y. Kambin's triangle approach of lumbar transforaminal epidural injection with spinal stenosis. Ann Rehabil Med. 2011;35(6):833–843. https://doi.org/10.5535/arm.2011.35.6.833

This technique has been offered as an alternative to the traditional safe triangle approach based on a theoretically superior anatomical argument. Park et al compared Kambin’s triangle to the subpedicular approach in terms of frequency of complications during the procedure and the effect of the transforaminal ESI at two and four weeks.

The researchers found no statistical difference in pain relief efficacy between the two methods at two and four weeks, but they did find that the Kambin’s triangle method resulted in less nerve root pricking, but not long-term damage.^[4] However, cases of intradiscal injections have been reported with Kambin’s triangle.^[7] In another study, researchers found that the Kambin’s triangle method was useful in situations where placing the needle at the anterior epidural space was difficult.^[6]

Kambin’s triangle offers an alternative method to the classic safe triangle approach for transforaminal ESI. Although both methods have pros and cons, Kambin’s triangle is less frequently used. However, it may have potential for being efficacious in situations where the safe triangle method is more technically difficult or more dangerous for patients. Larger-scale studies are required to effectively compare the two techniques head to head.

References

1. Lurie J, Tomkins-Lane C. Management of lumbar spinal stenosis. BMJ. 2016;352:h6234. https://doi.org/10.1136/bmj.h6234.
2. Vad VB, Bhat AL, Lutz GE, Cammisa F. Transforaminal epidural steroid injections in lumbosacral radiculopathy: a prospective randomized study. Spine (Phila Pa 1976). 2002;27(1):11–16. https://doi.org/10.1097/00007632-200201010-00005
3. Smith CC, Booker T, Schaufele MK, Weiss P. Interlaminar versus transforaminal epidural steroid injections for the treatment of symptomatic lumbar spinal stenosis. Pain Med. 2010;11(10):1511– 1515. https://doi.org/10.1111/j.1526-4637.2010.00932.x
4. Botwin KP, Gruber RD, Bouchlas CG, et al. Fluoroscopically guided lumbar transformational epidural steroid injections in degenerative lumbar stenosis: an outcome study. Am J Phys Med Rehabil. 2002;81(12):898–905. https://doi.org/10.1097/00002060-200212000-00003
5. MacVicar J, King W, Landers MH, Bogduk N. The effectiveness of lumbar transforaminal injection of steroids: a comprehensive review with systematic analysis of the published data. Pain Med. 2013;14(1):14–28. https://doi.org/10.1111/j.1526-4637.2012.01508.x
6. Park JW, Nam HS, Cho SK, Jung HJ, Lee BJ, Park Y. Kambin's triangle approach of lumbar transforaminal epidural injection with spinal stenosis. Ann Rehabil Med. 2011;35(6):833–843. https://doi.org/10.5535/arm.2011.35.6.833
7. Zhu J, Falco FJ, Formoso F, Onyewu O, Irwin FL. Alternative approach for lumbar transforaminal epidural steroid injections. Pain Physician. 2011;14(4):331–341.