Contrast Medium Volume Needed to Reach
Anterior Epidural Space via the Kambin Triangle
or Subpedicular Approach for Transforaminal
Epidural Injection
Authors: Ghai Babita 
Published: March 2021

Background: Transforaminal (TF) lumbar injection is a commonly used minimally invasive
intervention for management of chronic low back pain. TF injection can be performed using
various approaches to inject the drug to the anterior epidural space (AES).
Objectives: To identify the volumes of contrast medium needed to reach the AES and other
landmarks in the Kambin triangle (KB) and subpedicular (SP) approach of TF injection in patients
with lumbosacral radicular pain.
Study Design: Randomized controlled trial.
Setting: Pain clinic and operating room of a tertiary care hospital.
Methods: Seventy-five eligible patients were randomized to receive TF epidural injection either
by SP (SP group; n = 38) or the KB (KB group; n = 37) approach under fluoroscopic guidance. After
confirming the appropriate needle position, contrast medium was injected at 0.5 mL increments
up to 2 mL under intermittent fluoroscopy. Contrast medium volumes needed to reach specific
landmarks, that is, AES, medial to superior pedicle, medial to inferior pedicle, medial aspect of both
the superior, and neural spread, were recorded. Following this, 4 mL of the drug (0.5% lidocaine
1 mL + methylprednisolone 80 mg + 1 mL normal saline solution) was injected. Patients were
evaluated for Visual Analog Scale (VAS) and modified Oswestry Disability Questionnaire (MODQ)
scores after epidural injections at 2 weeks, 1 month, and 2 months.
Results: Average volume of contrast medium needed to reach AES was 1.10 ± 0.46 mL in the KB
approach and 1.10 ± 0.38 mL in the SP approach. Contrast medium volume needed to reach other
landmarks showed comparable results in both groups. AES was seen in 27.02% (10/37) patients
in the KB group and 23.6% (9/38) patients in the SP group with 0.5 mL of contrast medium. This
increased to 56.76% (21/37) and 77.7% (28/38) with 1 mL of contrast medium (P = 0.03, chi-square
test). No anterior spread was seen even after 2 mL of contrast medium in 4 patients in the KB group
and 2 patients in the SP group. Neural spread was seen in 100% of patients in the KB group after
0.5 mL of contrast medium, but in 34 (89.4%) patients in the SP group (P = 0.03, chi-square test).
We did not note any contralateral spread. Short-term effectiveness in pain relief in terms of VAS for
back pain and functional improvement in terms of MODQ score over time showed similar results in
both groups. Intravascular needle puncture and needle paresthesia was comparable in both groups.
Limitations: Small follow-up duration is one the limitations of this study. Future studies will be
needed to assess any long-term differences in outcome between approach methods. Also, use of
intermittent fluoroscopy might have limited detection of intravascular injections of the contrast
medium in comparison to the continuous fluoroscopy.
Conclusions: To conclude, our study revealed that average volume of contrast medium needed
to reach AES and other landmarks were comparable with both approaches of TF injection.
Key words: Transforaminal injection, subpedicular approach, Kambin triangle approach, contrast
medium spread, anterior epidural spread