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Background and Aims TLIP blocks the dorsal rami of the thoracolumbar nerves, as they pass through paraspinal musculature. The ESP block is performed by depositing the local anaesthetic between the deep fascia of the erector spinae muscle and the transverse vertebral process targeting the dorsal rami. Both are proven useful for spine surgeries. This study compares injectate spread of these interfascial plane blocks to better understand their mechanisms and to establish if there is any difference in the drug spread.

Methods Ultrasound guided TLIP or ESP block were given at L3 or L4 level in 4 cadavers (4 blocks each) with 20 ml of methylene blue. Classical TLIP was given between multifidus and longissimus and ESP was given between transverse process and erector spinae muscle. Anatomical dissection was carried out to look for spread to muscles, dorsal and ventral rami and epidural space

Results The dye spread has been demonstrated in table 1. Higher number of dorsal rami at the origin were stained in ESP block. However, the branches of dorsal rami between multifidus and longissimus were stained in all the blocks with similar craniocaudal spread. No spread was seen in the epidural space

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Abstract EP047 Figure 1

Spread in TLIP block

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Abstract EP047 Figure 2

Staining of dorsal rami (DR) with visualization of dorsal root ganglion (DRG) and ventral rami (VR) in ESP block

Conclusions TLIP block is an effective alternative to ESP block for spine surgery. The dorsal rami branches between the erector spinae group of muscles were equally involved in both the blocks. Surgeries involving the back with midline incision and no lateral extension may be well covered by TLIP block which is easier and superficial than ESP block