Anatomical evaluation of injectate spread in thoraco-lumbar interfascial plane block and lumbar erector spinae plane block: A cadaveric study.

Background and Aims: The erector spinae plane (ESP) block and the thoraco-lumbar interfascial plane (TLIP) block are commonly used for providing analgesia in spine surgeries. The extent of drug spread and its possible mechanism in TLIP block still remain to be elucidated. The aim of this study was to assess and analyse the spread of dye in classical TLIP block and ESP block in cadavers. Methods: This was an interventional study in six fresh frozen cadavers. Ultrasound-guided ESP and TLIP block was given at the L3 level on either side with 20 ml of methylene blue solution. Posterior lumbar region dissection was performed to analyse the dispersion and impregnation of the blue solution. Results: The multifidus and the longissimus were stained in both the blocks, while the iliocostalis was involved in ESP block. Craniocaudal block was similar in both the blocks from L2 to L4. The incidence of spread to the main trunk of dorsal rami was higher in ESP block (100%) versus TLIP block (33.3%). The spread to ventral rami was less consistent in ESP block (33.3%), while it was absent in the TLIP block. There was no reported dye stain in the epidural or paravertebral space. Conclusion: Both TLIP and ESP blocks show consistent L2-L4 craniocaudal spread. The anterior spread to the main trunk of dorsal rami was minimal and absent to ventral rami with TLIP block. On the other hand, the dorsal rami were stained consistently and lateral spread reached till iliocostalis in the ESP block.