A dorsal ultrasound-guided approach to perineural injection of the sixth and seventh cervical spinal nerves in horses is accurate and does not result in epidural placement.

Abstract

Objective: To determine the accuracy of a dorsal ultrasound-guided approach for perineural injection of the sixth and seventh cervical spinal nerves (CSNs) with the use of a clinically relevant volume of injectate (2 mL). We hypothesized that the majority of injections would result in identification of contrast solution in the intervertebral foramen (IVF) on CT and corresponding methylene blue dye staining of the CSN on postmortem evaluation, and distribution of injectate into the epidural space would not occur.

Methods: 7 horses donated to the University of Pennsylvania New Bolton Center for euthanasia were utilized. A dorsal ultrasound-guided perineural injection of the right and left sixth and seventh CSNs with the use of methylene blue and iohexol (2-mL volume) was performed. Postmortem CT of C5-C7 was performed and evaluated for presence of contrast within the IVF and epidural space. The cervical region was frozen at -20 °C prior to performing serial transverse band saw sections to evaluate for presence of methylene blue in contact with or surrounding the sixth and seventh CSNs and epidural space.

Results: Contrast was identified on CT in the IVF in 22 of 24 injections (92%). Methylene blue was adjacent to or surrounding the sixth and seventh CSNs in 22 of 24 injections (92%). No dye or contrast was noted within the epidural space.

Conclusions: This ultrasound-guided approach to caudal CSN perineural injection is highly accurate without high risk for epidural penetration.

Clinical relevance: This approach should be considered for injection of the sixth and seventh CSNs for conservative management of cervical radiculopathy.