Ultrasound-guided cranial multifidus cervicis plane block in dogs: a cadaveric study

Management of pain in the canine cervical spine is a challenge where regional anesthesia of the cervical dorsal branches via an interfascial plane approach can improve multimodal analgesia. This study aimed to describe the ultrasound-guided multifidus cervicis plane (US-MCP) approach in dogs and evaluate its distribution and nerve staining.

An anatomical and sonoanatomical study was followed by an experimental phase using 15 ultrasound-guided injections performed at the C3 level (0.3 mL kg^-1 of a methylene blue, iodinated contrast, and saline mixture) in canine cadavers. Contrast spread and nerve staining were evaluated using computed tomography (CT) and subsequent anatomical dissection.

Sonoanatomical landmarks were consistently identified in all cases. CT contrast spread reached the C1-C2 levels cranially and C4-C5 caudally in most cases. Contrast distribution reached the dorsal midline in 12/15 injections. Epidural migration occurred in 4/15 cases, mainly at the C2-C3 level. Dissection confirmed accurate interfascial deposition in all specimens. Nerve staining was 100% effective (15/15) for the dorsal branches of C2 and C3 and 60% in the case of C4 (9/15). However, success rates decreased caudally and staining was observed in 13.3% (2/15) of C5 nerves, and was absent (0/15) at C6.

The described US-guided MCP approach is a feasible and highly specific technique for the desensitization of the cranial dorsal cervical region. Consistent staining of the C2 and C3 dorsal branches, and potentially C4, supports its potential as a promising tool for integration into multimodal analgesia protocols. Clinical studies are required to evaluate its safety and analgesic efficacy.