Nerve Repair, Timing
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Over time, injured peripheral nerves retract and become scarred (days to weeks), the Schwann cells and endoneurial tube in the distal denervated nerve become less receptive to regenerating axons (especially with delays longer than 4 months), and muscles become atrophic and fibrotic, being replaced with adipose tissue (atrophy may appear as soon as a few weeks after injury, and fibrosis occurs predominantly after one year). Therefore, injured nerves should be repaired as soon as possible. However, most nerve injuries recovery without surgery, but this recovery is usually not evident until weeks or months after the injury; well beyond the time period when the above listed issues become problematic. Unfortunately, physical examination, electrophysiology, and imaging results often cannot determine which injured nerves will spontaneously recovery in time. To avoid operating on patients who have neuropraxic injuries and will recover spontaneously, the following rules have been developed.
Rules of 3
The "rules of 3" provide guidance on when to explore a focal nerve injury:
- 3 days - Sharp Transection - If there has been a documented sharp transection of a peripheral nerve without a simultaneous blunt or stretch injury, then the injured nerve should be repaired as soon as possible, or at least within 3 days. Examples include box-cutter injuries, many stab wounds, broken glass, and intraoperative transections with a scalpel blade.
- 3 weeks - Blunt Transection - This is when a nerve is transected or ruptured, but the proximal and distal nerve stumps have sustained additional blunt or stretch injuries. Repairing these nerves immediately, before the damage to the proximal and distal stumps become visibly evident (e.g., contusion, swelling), may cause the surgeon to sew together nerve segments that are destined to be scarred or neuromatous, thus precluding regeneration and recovery. When explored a few weeks later (e.g., 3 weeks), a more accurate microscopic evaluation and repair may be performed. Examples include, ax, chainsaw, propellar blade, and engine fan injuries. Blunt transections are more common than sharp transections.
- 3 months - Stretch/Uncertain - This is the most common type of nerve injury, and includes closed/blunt injuries, positional palsies, intraoperative injuries where the surgeon is quite sure they did not transect the nerve, and birth brachial plexus injuries. Most of these injuries are neuropraxic and recover within 3 months, therefore waiting this time excludes these patients from having unneeded surgery. When nerves are explored at 3 months, nerve action potentials are obtained, and if absent, nerve grafting or direct repair is performed. Prior to surgery, serial physical and electrophysiological examinations are performed, and if there is signs of early reinnervation, then surgery can be postponed longer. For brachial plexus injuries where multiple rootlet avulsions from the spinal cord are present, early surgery is often recommended (earlier than 3 months), because the chances of recovery without nerve transfers is very poor. High-resolution imaging of peripheral nerves with ultrasound or MRI may also provide anatomical evidence of nerve transection, which would encourage early exploration also.