Contrast Medium Volume Needed to Reach Anterior Epidural Space via the Kambin Triangle or Subpedicular Approach for Transforaminal Epidural Injection

Abstract

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). 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. Randomized controlled trial. Pain clinic and operating room of a tertiary care hospital. 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. 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. 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. 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. Transforaminal injection, subpedicular approach, Kambin triangle approach, contrast medium spread, anterior epidural spread.