Nerve Injury and Repair Flashcards
What technical advancement has allowed routine attempts at surgical repair of nerves in the 20th century?
The availability of surgical microscopes
What is the most basic subunit of the peripheral nerve?
The Axon
What is each axon surrounded by?
Endonurium
Axons are grouped into what unit?
Fascicles
What makes up the interfascicular space?
Epineurium
The main nerve is surrounded by what sheath?
The external epineurial sheath
What is the name of the external connective tissue that holds the blood supply to peripheral nerves and allows gliding during normal range of motion?
Mesoneurium
Why do distal nerve repairs correlate to better functional status?
Proximally, fascicular topography allows significant intermingling of sensory and motor fibers, but as you move distally in a nerve, the fascicles become more distinctly grouped/differentiated
After nerve injury, what happens to the proximal portion of the nerve?
It dies back to the nearest node of Ranvier and eventually regrows from multiple “growth cones” in an attempt to grow into the distal endoneurial tube
After nerve injury, what happens to the distal portion of the nerve?
It undergoes Wallerian degeneration, where the myelin sheath and debris are phagocytosed and the axon is replaced over 3-6 weeks - it is capable of accepting new axon sprouts
Why are the first 72 hours important in a nerve injury
The distal nerve can still transmit electrical stimulation and can be located with electrical stimulation in the OR
What are the zones of injury in a nerve
Neurapraxia, axonotmesis, and neurotmesis
What is Neurapraxia?
The least severe zone of nerve injury (scalpel injury, for example) which heals in das to months without intervention
What is Axonotmesis?
The second most severe nerve injury - depending on degree, may have complete or no recovery without intervention, since wallerian degeneration takes lace and recover is based on on degree of scar tissue within endoneurial or perineurial sheaths
What is Neurotmesis?
The third and most severe degree of nerve injury, for which only operative repair or grafting will result in recovery
How quickly do axons grow?
1 inch per month or 1mm per day
What are the benefits of exploring an open nerve injury immediately?
- Identification of distal nerve with electrical stimulation, 2. Primary repair of nerve is possible, 3. Tagging nerves for later definitive repair, when injury has declared itself, so as to avoid suturing through scar
How do you deal with nerve injury in a closed wound
Close follow up, as it may just be neurapraxia and self limited. Monitor with non-invasive testing over weeks to months
What timeline is there for definitive motor neuron repair?
4-6 months, to allow regenerating axons time to grow into target muscle
How do you deal with nerve injuries from gunshot wounds?
Treat as closed injury - most of the time, it is neurapraxia or axonotmesis from blast injury
What is nerve ending preparation?
Adequate resection of damaged portion of nerve until a flush, healthy fascicular pattern is identified - ley yeux d’escargot (eyes of a snail) - so that the fascicular bundles align on repair
True/False: It is acceptable to do a nerve graft to avoid a repair with tension
True - it is essential that there by no tension whatsoever in a nerve repair
What is epineurial nerve repair?
Suturing only the external epineurial vessels with the fascicles aligned
What is grouped fascicular repair of a nerve?
Suturing internal epineurium together when excellent fascicular topography is visualized
