Inadvertent injection of particulate steroids into the vertebral artery during cervical nerve root blocks has been postulated to be an etiology of some catastrophic complications that might be avoided with non-particulate steroids. This study evaluated the effects of direct vertebral artery injection of particulate and non-particulate steroids in an animal model.

Pigs underwent direct injection into their vertebral arteries under fluoroscopic guidance. Group 1 was injected with the particulate steroid Depo-Medrol (1ml 40mg/ml), while the control Groups 2 (1ml Solu-Delta 50mg/ml) and Group 3 (Decadron 1ml 4mg/ml) received non-particulate steroids. Following injection, the pigs were appropriately recovered and scheduled to undergo MRI the following day, after which they were sacrificed. Brain and spinal cord material were retrieved, fixed in paraformaldehyde for 1 week, followed by histopathologic analysis.

A total of 11 pigs were injected. 4 were injected with Depo-Medrol, 3 with Solu-Delta and 4 with Decadron. All pigs injected with Depo-Medrol failed to regain consciousness and required ventilatory support. According to the protocol, they were sacrificed following MRI obtained 4 hours following the injections. The pigs that underwent Solu-Medrol and Decadron injection recovered fully and demonstrated no evidence of neurologic injury. They then underwent MRI the following day, and were sacrificed according to the protocol. MRI data revealed upper cervical cord and brain stem edema in the Depo-Medrol group, but not in the Solu-Medrol or Decadron groups. Histologic analysis showed early evidence of hypoxic/ischemic damage in the Depo-Medrol group but not in the Solu-Medrol or Decadron groups.

The data suggest that one etiology of neurologic complications following cervical nerve blocks may be due to inadvertent vertebral artery injection of particulate steroids, as all pigs injected with Depo-Medrol suffered neurologic deficits while none of the controls injected with soluble steroids were affected.