Anatomical evaluation of the extent of spread in the erector spinae plane block: a cadaveric study Translated title: Évaluation anatomique de la propagation du bloc du plan des muscles érecteurs du rachis: une étude cadavérique

In this overview, new and existent material on the organization and composition of the thoracolumbar fascia (TLF) will be evaluated in respect to its anatomy, innervation biomechanics and clinical relevance. The integration of the passive connective tissues of the TLF and active muscular structures surrounding this structure are discussed, and the relevance of their mutual interactions in relation to low back and pelvic pain reviewed. The TLF is a girdling structure consisting of several aponeurotic and fascial layers that separates the paraspinal muscles from the muscles of the posterior abdominal wall. The superficial lamina of the posterior layer of the TLF (PLF) is dominated by the aponeuroses of the latissimus dorsi and the serratus posterior inferior. The deeper lamina of the PLF forms an encapsulating retinacular sheath around the paraspinal muscles. The middle layer of the TLF (MLF) appears to derive from an intermuscular septum that developmentally separates the epaxial from the hypaxial musculature. This septum forms during the fifth and sixth weeks of gestation. The paraspinal retinacular sheath (PRS) is in a key position to act as a 'hydraulic amplifier', assisting the paraspinal muscles in supporting the lumbosacral spine. This sheath forms a lumbar interfascial triangle (LIFT) with the MLF and PLF. Along the lateral border of the PRS, a raphe forms where the sheath meets the aponeurosis of the transversus abdominis. This lateral raphe is a thickened complex of dense connective tissue marked by the presence of the LIFT, and represents the junction of the hypaxial myofascial compartment (the abdominal muscles) with the paraspinal sheath of the epaxial muscles. The lateral raphe is in a position to distribute tension from the surrounding hypaxial and extremity muscles into the layers of the TLF. At the base of the lumbar spine all of the layers of the TLF fuse together into a thick composite that attaches firmly to the posterior superior iliac spine and the sacrotuberous ligament. This thoracolumbar composite (TLC) is in a position to assist in maintaining the integrity of the lower lumbar spine and the sacroiliac joint. The three-dimensional structure of the TLF and its caudally positioned composite will be analyzed in light of recent studies concerning the cellular organization of fascia, as well as its innervation. Finally, the concept of a TLC will be used to reassess biomechanical models of lumbopelvic stability, static posture and movement.

The erector spinae plane block (ESPB) was first described in 2016 as a regional block for thoracic neuropathic pain. Given its short history, there are a paucity of controlled clinical trials, yet an abundance of case reports. The primary aim of this review is to examine pooled clinical data from published literature to gain an understanding of ESPB characteristics.

Postoperative pain after bariatric surgery can be significant and yet difficult to manage. These patients frequently have associated obstructive sleep apnea and are at risk of respiratory depression with opioid analgesia. Abdominal wall blocks such as the subcostal transversus abdominis plane block are not of significant benefit, probably in part because they provide only somatic analgesia. The ultrasound-guided erector spinae plane (ESP) block is a recently described regional anesthetic technique for providing thoracic analgesia when performed at the level of the T5 transverse process. Local anesthetic injected into the fascial plane deep to the erector spinae muscle spreads in a craniocaudal fashion over several levels. Local anesthetic also penetrates anteriorly through the intertransverse connective tissue and enters the thoracic paravertebral space where it can potentially block not only the ventral and dorsal rami of spinal nerves but also the rami communicantes that transmit sympathetic fibers. Coupled with the fact that the erector spinae muscle and ESP extend down to the lumbar spine, this suggests that the ESP block could result in both visceral and somatic abdominal analgesia if the injection were performed at a lower thoracic level. We describe a series of 3 cases that illustrate the efficacy of bilateral ESP blocks performed at the level of the T7 transverse process for relieving visceral abdominal pain following bariatric surgery. Further investigation is recommended to establish the potential of the ESP block as an analgesic modality in abdominal surgery.