OrthoNet

Peripheral Nerve Injuries - Management

Indications for Surgery

Sunderland I - neuropraxic
Sunderland II - axonotmetic
Sunderland III - perineurium preserved
Sunderland IV - incomplete disruption of perineurium
Sunderland V - neurotonmesis

The trick is in distinguishing the Sunderland I, II, and III injuries from the IV and V, and recognizing what the surgery can actually accomplish.
- Clinical examination
- Electrophysiologic testing

Closed injury - the lesion in continuity
Open injury - laceration or blast

? Role for early exploration ?
- less scarring makes the dissection easier
- intraoperative evaluation of the anatomy, and possibly with
electrophysiologic means, the function of the nerve
- early repair with potential for faster recovery

- Is it worth the risk of operating on those who will
improve on their own?

Timing of Surgery

Biological considerations:

- Wallerian degeneration - axons, endoneurial tubes, cell bodies
- Motor end plates - 12-24 months
- Muscle - atrophy and suicide genes
- Sensory end-organs - undefined survival time
- Axonal regenerative capacity - 2.5 cm per month

EMG changes - transient fibrillation potentials - spontaneous fibrillations (membrane instability)

Technical considerations:

- Type of injury - laceration, crush, avulsion
- Type of wound - open or closed
- Condition of open wound - clean, contaminated

For sharp transections in a clean environment - immediate repair

For contaminated wounds - initial debridement and tagging of ends, followed by secondary repair.

For closed injuries - 3-6 months of observation.

The outcomes of all methods of treatment, including neurolysis, nerve repair, and nerve grafting, deteriorate after 6 months.

Surgical Management

Mobilization - the 2.5 cm gap

Epineurial repair with 9-0 or 10-0 monofilament suture

Fascicular repair versus epineurial repair?

Nerve Loss
- tension causes gapping, increased intraneural fibrosis, and decreased blood flow
- methods of closing gaps
- how much is too much tension?
- mind the 2.5 cm threshold!

Nerve Grafts
- sural nerve
- lateral antebrachial cutaneous nerve
- medial antebrachial cutaneous nerve

Beyond the surgeon’s control:
- patient age
- level of injury

Current and Future Possibilities

Coaptation Techniques

- CO2 laser and argon laser welding
- fibrin gluing

Nerve Conduits

- bone
- silicone
- vein ? + Schwann cells or neurotrophic factors
- artery
- polyglactin 910
- collagen

Allografts

- immunologic rejection vs immungenicity
- irradiation, lypholization, freeze-drying - all reduce antigenicity
- cyclosporin and FK506 - immunosuppression
- effect on allograft Schwann cells

FK506 - Tacromilus

- promotion of functional nerve recovery

Enhancement of Nerve Regeneration

Full recovery of function after nerve transection is rare.
Motor end-plates have a finite life span after dennervation - the axonal growth must reach the target organs in time.
Neuronal survival is critical.

SPEED and SURVIVAL

Neurotrophic Factors

Nerve Growth Factor - NGF
- multiple and varied effects inside and outside the nervous system
- receptor mRNA is upregulated after experimental injury
- motor neurons lack trkA receptors; unlikely that NGF will have much effect on motor nerve injuries

Brain Derived Neurotrophic Factor - BDNF
- growth and survival factor for motor neurons, prevents natural apoptosis
- strong evidence to support its role in axonal and neurite regeneration in motor neurons in particular.

Neurotrophin 3 - NT-3
- role in CNS regeneration (spinal cord)
- sensory and parasympathetic neurons
- motor neuron survival
- motor endplates

Enhancement of Nerve Regeneration

Neurotrophin 4/5 (NT-4/5)
- survival of motor neurons
- modulates neurmuscular junction in axotomized motor neurons
- increased ability of motor neurons to innervate skeletal muscle fibers

Ciliary Neurotrophic Factor (CNTF)
- neurite