Anatomical evaluation of the extent of spread in the erector spinae plane block: a cadaveric study

The erector spinae plane (ESP) block is an interfascial analgesic technique first described as an alternative for pain control at the thoracic level. The objective of this observational study was to determine the anatomical spread of dye following a T7 ESP block in a cadaveric model.

An ultrasound-guided ESP block was performed in four fresh human cadavers using an in-plane approach with a linear probe in a longitudinal orientation and a puncture in a craniocaudal direction. Twenty millilitres of an iodinated contrast/methylene blue solution was injected deep to the erector spinae muscle at the distal end of the T7 transverse process bilaterally in two of the specimens, and unilaterally in the other two (six ESP blocks in total). Subsequently, the specimens were subjected to a multi-slice computed tomography (CT) scan with three-dimensional reconstruction. Two of the specimens were dissected to evaluate the distribution of the contrast solution, and a sectional study was performed in the other two.

In the six samples, evaluated by CT scan and anatomical dissection, a craniocaudal spread of the dye was observed in the dorsal region from T1-T11 with lateral extension towards the costotransverse region. No diffusion of contrast solution or dye to the anterior region (paravertebral space) was observed by CT scan or dissection.

The results suggest that the ESP block reaches a wide range of the posterior rami of spinal nerves without diffusion into the paravertebral space or involvement of the anterior rami.