[Morphological changes after permanent nerve block by freezing and ethanol injection of the sciatic nerve of the...

Permanent nerve blocks by intraneurally injected alcohol are often complicated by alcohol-neuritis. Encouraging clinical experiences with permanent blocks by freezing raises the question whether morphological differences between the nerve lesions could explain the difference in their side effects. On 30 rabbits both sciatic nerves were blocked after surgical preparation. The one by intraneural injection of 0,5 ml of 96% Ethanol, the other by freezing with a cryoprobe. The resulting degeneration and the beginning of recovery of the nerves was followed by histological evaluations of the sciatic nerves during the first 28 days after the blockade. The nerve lesions of both types of blockade were complete. That produced by the cryoprobe was limited to the small area of local freezing, whereas the alcohol-block produced the same type of nerve degeneration but with a wide-spread extension reaching the sacral plexus. We discuss whether this slight morphological difference might be sufficient to explain the higher complication rate of alcohol blocks.