Spread of local anesthetic injected in the paravertebral space, intertransverse processes space, and erector spinae plane: a cadaveric model

Introduction Paraspinal fascial plane blocks have become popular and include the erector spinae plane (ESP) and intertransverse process (ITP) blocks. Controversy exists regarding the exact mechanism(s) of these blocks. We aimed to evaluate the spread of local anesthetic (LA) following ESP and ITP blocks as compared with paravertebral (PV) blocks in a cadaveric model. Method Single-injection ultrasound guided ESP (n=5), ITP (n=5), and PV (n=5) blocks were performed in 15 fresh cadaver hemithoraces. The extent of LA spread within the erector spinae fascial plane, involvement of the dorsal ramus, and distribution within the PV space, were qualitatively described. Results The spread of LA following ESP block extended eight vertebral levels in a cranio-caudal direction, involving the dorsal ramus at each level, but without LA spread into the PV space nor to the ventral rami. LA spread following ITP block extended 1–2 vertebral levels within the PV space and 7 vertebral levels within the erector spinae fascial plane. The spread of LA following PV blocks extended 2–4 vertebral levels, involving the ventral and dorsal ramus at each level, but without LA spread into the ESP. Conclusion Based on the results of this cadaveric experimental model of paraspinal fascial plane blocks, LA spread following ITP blocks extends into both the PV space and the erector spine fascial plane, and thus may offer a more favorable analgesic profile than ESP blocks.