The spread of the ultrasound-guided injectate after a lumbar and thoracic erector spinae plane block. A cadaveric study

Purpose : The erector spinae plane block is a novel block performed at a thoracic level with a spread via the thoracolumbar fascia. The objective of this cadaveric study is to evaluate the spread of the injectate after a lumbar erector spinae plane block. Methods : Four lumbar erector spinae blocks were perfonned in two non-embalmed cadavers with 20 ml of a methylene blue or black ink solution injected in a plane between the transverse processes and the erector spinae muscles. After dissection, the extent of the dye spread, and the staining of neuronal structures were documented. Laminectomy was performed to determine the epidural spread. A thoracic erector spinae plane block was also performed in both cadavers to determine the epidural spread of dye. Results : In the lumbar region, the craniocaudal dye spread underneath the erector spinae muscle varied between two and five intervertebral levels. The staining of the spinal nerves was limited to the level of the intervertebral foramina in one cadaver. Dye was also observed at the inner side of the ligamenta flava at the lumbar region. An epidural spread was present after both thoracic erector spinae blocks, with an extension to the contralateral side in one of them. Conclusion : A lumbar erector spinae block (ESB) can spread over multiple vertebral levels in the proximity of the neuroforamen and the spinal nerves and, potentially to the epidural space. This may suggest analgesia for lower spine surgery. A thoracic ESB may spread epidurally and contralaterally. Further research is desirable.