Kara A. Brown, Julie B. Engiles, Cristobal Navas de Solis, Kathryn W. Bills, Amy L. Johnson, Elizabeth J. Davidson
Background
Cervical radiculopathy, resulting from cervical nerve root compression, is increasingly recognized as a cause of neck pain and poor performance in horses. Existing injection techniques for managing cervical nerve inflammation are limited by imprecise targeting and risk of epidural or vascular penetration. Prior studies lacked in-vivo data, used large injectate volumes, and didn’t confirm safety in live horses. This study evaluated a novel dorsal ultrasound-guided approach to inject the sixth (C6) and seventh (C7) cervical spinal nerves (CSNs) using a clinically relevant (2 mL) volume, aiming to determine its accuracy and safety in live equine subjects.
Methods
Seven horses (6 live, 1 cadaver) underwent ultrasound-guided perineural injections of the left and right C6 and C7 CSNs with 2 mL of a methylene blue and iohexol solution. Post-injection, horses were euthanized, and cervical spinal segments were imaged using helical CT to assess contrast localization. Serial transverse sections were then performed to evaluate dye distribution to the CSNs and check for epidural or muscular infiltration. One specimen underwent histological examination.
Results
In 22 of 24 injections (92%), CT confirmed contrast in the intervertebral foramen (IVF), and methylene blue was found adjacent to or surrounding the C6 and C7 CSNs. No cases showed dye or contrast in the epidural space. Injectate consistently diffused into adjacent musculature, particularly the brachiocephalicus. Horses tolerated the procedure well without adverse events. Histology showed no injection-induced damage. The approach provided precise needle placement with minimal risk of epidural or vascular penetration.
Limitations
Dye diffusion properties may not fully mimic clinical agents like corticosteroids. Variability in timing between injection, euthanasia, and freezing may have influenced injectate distribution. Histopathologic assessment was limited to a single section and could not fully evaluate subtle adverse effects or vascular involvement. Serial sectioning lost 2 mm of tissue per slice, potentially missing some dye localization.
Conclusions
The dorsal ultrasound-guided technique for perineural injection of C6 and C7 CSNs in standing, sedated horses is highly accurate and carries a low risk of inadvertent epidural or vascular injection. This method improves upon previous techniques and offers a safer, ergonomically favorable approach for nonsurgical management of equine cervical radiculopathy. Further studies are needed to evaluate clinical outcomes, optimal medication choices, and long-term safety.
Sonographic image utilizing a 3- to 8-Hz curvilinear probe oriented in a transverse plane perpendicular to the long axis of the cervical vertebral column, demonstrating the approach to injection of the seventh cervical spinal nerve directly adjacent to the vertebral vein and artery at the ventral aspect of the cranial articular process. A = Vertebral artery. APJ = Articular process joint. N = Nerve. V = Vertebral vein.
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