Percutaneous Transforaminal Epidural Injection Method in an Experimental Rat: Minimally Invasive Drug Delivery Method to Spinal Epidural Space

OBJECTIVE To compare a newly developed minimally-invasive method for percutaneous transforaminal epidural injection (INJ group) with the existing method for lumbar epidural catheterization (CATH group). METHOD Through anatomical review of experimental rats, the cephalic one fourth of the neural foramen was selected as the target point for drug delivery. After the rats had undergone lumbar epidural catheterization, lidocaine, and 1% methylene blue were injected through the unilateral or bilateral L5/6 neural foramen in the INJ group, and through an epidural catheter in the CATH group. Measurement of body weight and the mechanical allodynia test before and after injection of lidocaine, and fine dissection after injection were performed. RESULTS Results of the mechanical allodynia test of 1.0% lidocaine 50 µl injection in the CATH group were statistically similar to those of 0.5% lidocaine 100 µl injection in the INJ group. The results of 2.0% lidocaine 50 µl injection in the CATH group were statistically similar to those of 1.0% lidocaine 100 µl injection in the INJ group. After dissection, only one distal partial spinal nerve was stained by methylene blue 50 µl through the transforaminal pathway. However, the dorsal root ganglion, nerve root, and adjacent hemi-partial spinal cord were stained by methylene blue 100 µl through the transforaminal pathway. CONCLUSION The percutaneous transforaminal epidural injection is practical, easy, and safe, and, in particular, does not cause significant pain compared to the existing lumbar epidural catheterization. We expect this method to be effective in an animal study showing that drug delivery to the spinal epidural space is necessary.