Cadaveric study of the ultrasound-guided erector spinae plane block over the dorsolateral edge of the transverse process of the ninth thoracic vertebra in dogs: transverse vs. longitudinal approach

IntroductionStudies of the ultrasound-guided thoracic erector spinae plane (ESP) blocks in dogs are limited. This study aimed to describe a transverse (TV) ultrasound-guided ESP approach at the dorsolateral edge of the transverse process (DLETP) of T9, compare its distribution with a longitudinal (LNG) approach, and analyze the thoracic transverse process anatomy.MethodsTwenty-three canine cadavers were used in this double-blinded experimental study. An ESP injection using 0.6 mL/kg of dye/contrast was performed on each lateral of 21 cadavers with a TV or LNG approach at T9, followed by computed tomography and dissection.ResultsFive cadavers were excluded from dissection analysis. All TV injections were placed over the DLETP, whereas 18.75% of LNG injections were misplaced laterally. Both approaches produced craniocaudal spread within the ESP, with median (range) spreads of 8 (5–14) and 8.5 (4–13) vertebrae for the TV and LNG groups, respectively. Cranial spread exceeded caudal in the TV group, with 4.5 (2–6) vs. 3.5 (0–7) vertebrae (p = 0.027), and LNG, with 5 (3–7) vs. 3 (0–6) (p = 0.004). Staining of the medial branches of the dorsal rami (MBDR) of the spinal nerves showed median (range) values of 5 (4–8) and 5 (0–6) in TV and LNG. Cranial MBDR staining predominated in TV, with 4.5 (1–6) over caudal with 1 (0–3) (p = 0.003), and LNG, with 4 (0–6) vs. 0 (0–3) (p < 0.001). Lateral branches (LBDR) staining showed 4 (1–9) and 4 (2–12) in TV and LNG. Cranial LBDR staining exceeded caudal in TV, with 3 (0–6) vs. 1 (0–3) (p = 0.019), and LNG, with 3 (1–8) vs. 1 (0–5) (p = 0.034). Ventral branches staining occurred in 10/16 TV injections (62.5%) and 11/16 (68.75%) LNG. Both approaches showed epidural and sympathetic trunk spread while one intravascular injection occurred in LNG. No significant differences were found between approaches. The DLETP was predominantly absent caudal to T10 and smaller than the transverse process (p < 0.001).ConclusionThe TV and LNG approaches produced comparable nerve staining and ESP spread at T9 in dogs, with preferential cranial distribution. The TV approach reduced injectate misplacement. The DLETP was smaller than the transverse process and consistently identified cranial to T11.