Peripheral Nerve Injuries, Brachial Plexus, and Compression Neuropathies


Chapter 12

Peripheral Nerve Injuries, Brachial Plexus, and Compression Neuropathies



General Nerve Anatomy



1. The central nervous system (brain and spinal cord) communicates with the rest of the body via the peripheral nervous system (cranial nerves, spinal nerves with their roots and rami, peripheral nerve trunks/branches, and the autonomic system).


2. The anterior (ventral) and posterior (dorsal) nerve roots arise from rootlets on the spinal cord and merge into the spinal nerves (see Figure 12.1).


• The anterior primary rami of spinal nerves C5-T1 form the brachial plexus of the upper extremity, whereas the posterior primary rami of the spinal nerves travel to supply the muscle and skin of the posterior neck and trunk.



3. The motor nerve cell body is located within the spinal cord, and the sensory nerve cell body is located in the dorsal root ganglia.


4. Peripheral nerves are surrounded by Schwann cells that create the myelin sheath surrounding myelinated nerve axons.


5. Between each individual Schwann cell is the node of Ranvier that allows for faster propagation of signals down an axon through saltatory conduction.


6. Bundled axon nerve fibers are surrounded by endoneurium and grouped with other neurons by a collagen layer called perineurium. This group of neurons is termed a fascicle.


• Within a peripheral nerve, the fasicles are also imbedded in loose connective tissue composed of collagen and fibroblasts (the epineurium; see Figure 12.2).


7. The vascular supply of the nerve consists of segmental blood vessels that branch into several vascular plexuses along the epineurium and within the perineurium and endoneurium.


• This redundancy allows nerve mobilization over extended lengths without disruption of blood supply.







General Nerve Repair Principles



1. Closed nerve injuries should be treated conservatively with observation for signs of recovery.


• Consideration for electrophysiologic testing should be deferred until at least 4-6 weeks after injury, and many can wait until 3 months.


▪ If at 3 months there is no sign of recovery, nerve exploration is warranted.


▪ If partial spontaneous recovery is identified within 3 months, regular reevaluation with electrophysiologic testing can occur at 3-month intervals to observe continued recovery.


2. Open nerve injuries should be explored immediately.


• If the nerve is found to be in continuity, treat as above as if it were a closed injury.


• If the nerve is discontinuous, attempt immediate repair (unless significant crush injury, wound, or gunshot wound).


3. Nerve repair can occur either immediately or after delay.


• Direct immediate repair


▪ Method of choice, especially if performed within 48 to 72 hours


▪ Best outcomes


▪ Technically easier than delayed repair


○ Less retraction of nerve ends


○ Less scarring


○ Identification of nerve ends is easier because the nerve can often be stimulated for up to 72 hours after transection.


• Delayed repair


▪ Typically requires a nerve graft


▪ Impaired functional outcomes (see Table 12.1)



Table 12.1


Differing Treatments for Different Types of Nerve Injury



































TYPE OF NERVE INJURY NEUROGRAPHY/EMG EXPLORATION REVISION REPAIR OR RECONSTRUCTION
Sharp transection — Immediate Immediate Immediate
Open wound: Nerve crush injury 4-6 weeks* Immediate Immediate Immediate†
Delayed‡
Closed traction injury 4-6 weeks Delayed — 3-4 months§
Open wound: Gunshot wound 4-6 weeks* Immediate Immediate Immediate†
Delayed‡


image



*If the nerve is in continuity on exploration, can perform neurography/EMG in the same manner as that for closed injuries.



†If there is macroscopic nerve discontinuity on exploration, perform repair or reconstruction after repeated revision to ensure that the wound is tidy.



‡If there is nerve continuity on exploration, treat the nerve injury as a closed injury so that repair or reconstruction is performed only when there is no sign of nerve regeneration (Tinel’s sign), for example, for some injuries, exploration after 3-4 months.



§Repair or reconstruction is performed after 3-4 months if there are no clinical signs of nerve regeneration or reinnervation.


EMG, Electromyogram.


Reprinted from Neligan, P.C., Chang, J. (Eds.), 2013. Plastic Surgery, vol. 6, 3rd ed. Elsevier, 694–718.


4. Primary repair must occur without tension; otherwise, consider a nerve graft.


• For nerve gaps <3 cm, nerve conduits (e.g., synthetic, vein) can be used.


• For nerve gaps >3 cm, nerve grafts are recommended.


▪ Common donor grafts: Sural n., posterior interosseous n., lateral antebrachial cutaneous n.


▪ Grafts are preferably reversed at the time of placement to decrease the risk of nerve axon regeneration through cut branches on the graft.


5. Nonviable tissue must be resected until healthy fasicles are identified.


6. Alignment of the nerve ends according to their fasicular pattern and topographical arrangement improves outcomes.


7. Nerve ends are commonly coapted with interrupted 9-0 or 10-0 nylon sutures.


• Repair can occur at the epineurial or fasicular level.


• Grouped fasicular repair is preferred for injuries to the ulnar n. at the wrist.


8. If the proximal stump is absent, or if the nerve injury is “high,” and end-to-side nerve repair can be performed in which the distal stump end is coapted to the side of an uninjured nerve.


9. Nerve transfer is a newer technique that has primarily been used with proximal or brachial plexus injuries to provide a source of regenerating axons in close proximity to the end target and preserve motor end plates.


• In some cases, these transfers are performed as a “babysitter” to maintain motor end plates while a proximal injury is allowed to recover.


• Nerve transfers are associated with minimal to no downgrade in donor function and provide better outcomes (see Box 12.1 and Figure 12.4).





Brachial Plexus



1. Formed from the anterior primary rami of spinal nerves C5 to T1


2. Motor nerve cell bodies arise from the anterior horn of the spinal cord, whereas the sensory nerve cell bodies are located in the dorsal root ganglion within the intervertebral foramen, immediately outside of the dura mater.


3. The brachial plexus is commonly divided into five anatomic sections: Roots, trunks, divisions, cords, and branches


4. The mixed spinal nerves travel between the anterior scalene m. and the middle scalene m. to form three trunks.


• Upper trunk: C5 and C6


• Middle trunk: C7


• Lower trunk: C8 and T1


5. Beneath the clavicle, each trunk divides into anterior and posterior divisions.


6. Distal to the clavicle, the nerves exchange fibers to form cords.


• Lateral cord


▪ Formed from the anterior divisions of the upper and middle trunks


▪ Passes anterior to the subclavian artery


▪ Gives rise to the lateral cord contribution to the median n. and the musculocutaneous n.


• Medial cords


▪ Formed from the anterior division of the lower trunk


▪ Passes anterior to the subclavian artery


▪ Gives rise to the medial cord contribution to the median n. and the ulnar n.


• Posterior cord


▪ Formed from the posterior divisions of all trunks


▪ Passes posterior to the subclavian artery


▪ Forms the axillary nerve and the radial nerve (see Figures 12.5 and 12.6)


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Sep 2, 2016 | Posted by in Aesthetic plastic surgery | Comments Off on Peripheral Nerve Injuries, Brachial Plexus, and Compression Neuropathies

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