Peripheral nerve surgery
Peripheral nerve system is a network of 43 pairs of nerves that supply motor and sensory fibres throughout the human body. These may be affected by trauma, tumor etc. apart from various medical conditions like diabetes. Another common eitiology is compression of nerves at specific sites.
Timing is essential in treating these, since in significant injuries only early intervention can result in better prognosis. Compression syndromes are dealt with releasing the compressive element
Neuropraxia- which is the least severe form of injury usually recovers in 3 weeks time. If nerves are transected or injured, either from trauma or tumor removal, nerve surgery is recommended. Nerve surgery includes- neurolysis, primary repair, nerve grafting, and nerve transfers and in some cases free function muscle transfers. Late presenting cases are dealt with secondary surgical procedures like tendon transfers or joint arthrodesis.
- Neuropraxia- usually resolves by itself within 3 weeks
- Reinnervation – occurs in two ways- a) collateral branching b) regeneration of injured axons
- Collateral Branching– usually nerve injuries with 20-30% axonal damage heal with collateral branching. The process starts in 4-6 days and may continue upto 3-6 months. There are more axonal sprouts and thus there is initial muscle hypertrophy which is later balanced by the atrophied muscle fibres that are denervated.
- Regeneration of Axons– nerves with more than 90% axonal transection, nerve regeneration is the primary process of healing. 3 stages-
- Wallerian degeneration- happens in the 1 st week of insult. The distal stump undergoes granular disintegration of its cytoskeleton while the proximal stump undergoes disintegration upto the first node of Ranvier. These produce a micro-environment conducive for axonal regrowth.
- Axonal Regeneration- Axonal injury with an intact endoneurial tube and injuries more distal to the neuron have a better recover than proximal injuries. These axonal outgrowths become remyelinated with Schwann cells that is thinner than the original. Axonal outgrowth occurs at about 1mm/day.
- End- Organ Reinnervation- once the nerve reaches the target organ to be innervated, recovery is still possible only if the end organ is maintained. A stable end oragn includes a stable neuromuscular junction in case of motor neurons and sensory organs like Paccinian corpuscles, Meissner corpuscles. While muscle fibres atrophy as early as 3 weeks, NMJ integrity may be maintained upto 1 year. After 2 years irreversible muscle fibrosis occurs and nerve repair requiring recovery period exceeding 2 years (from insult) is not attempted. Sensory organs are preserved for about 2-3 years, so sensory recovery may continue even if muscle function is lost.