Page 63 - Read Online

to the muscle for maintenance of muscle health while proteins, including growth factors and adhesion
[19]
the proximal motor nerve is regenerating. [9‑11] A donor molecules, to create a growth‑rich milieu. In addition,
sensory nerve is thought to provide trophic support to the native endoneurial conduits guide the reestablishment
denervated muscle until the native motor axon is able to of neuromuscular connections. Research shows that
[12]
regenerate and reinnervate its target. In essence, sensory preservation of the original motor endplates is essential
protection provides an interim protective effect on the for precise contact, synaptic differentiation, and
denervated muscle prior to surgical nerve reconstruction. maintenance of reestablished neural connections. [20,21] This
growth‑supportive environment is significantly diminished
We performed an extensive literature search using if reinnervation does not occur in a timely manner.
[2]
PubMed, Ovid, and Embase databases using keywords Although the exact timeframe is debatable, Sulaiman and
“sensory”, “nerve”, “protection”, “regeneration”, and Gordon proposed a 4‑week window for nerve repair,
[22]
“denervation” to find primary articles reporting on the after which the motor neuron has diminished ability to
treatment and outcomes of the sensory protection either regenerate axons into the distal nerve stump.
in humans or animal models. This paper discusses the
three main approaches to sensory protection and reviews Both time and distance limit spontaneous reinnervation
the literature for each. We set the framework for future of muscles. When immediate nerve reconstruction is
studies and advocate for further investigation of sensory not possible, sensory protection is the most effective
protection in the upper extremities. means of providing temporary trophic support to
prevent muscle degeneration. The three surgical
MUSCLE DENERVATION AND techniques for sensory protection include: (1) end‑to‑end
REINNERVATION neurorrhaphy, (2) end‑to‑side neurorrhaphy, and (3) direct
muscle neurotization. Nerve transfers with end‑to‑end
neurorrhaphy or end‑to‑side neurorrhaphy are the most
Nerve injury and muscle denervation commonly used approaches for sensory protection.
The peripheral nervous system has a remarkable capacity End‑to‑end neurorrhaphy joins the ends of a transected
for regeneration following nerve injury. When a peripheral motor nerve and sensory nerve while end‑to‑side
nerve is severed, it undergoes Wallerian degeneration and neurorrhaphy connects the end of a transected donor
triggers a cascade of biochemical changes allowing future sensory nerve to the side of the injured motor nerve
regrowth. Muscle fibers maintain viability immediately stump. Neurotization, the third and least favored
following denervation, however, atrophic changes such approach, is the direct implantation of a divided sensory
as reabsorption of myofibrils, shrinkage of muscle cells, nerve into the belly of a denervated muscle. Figure 1
and expansion of the extracellular matrix with collagen illustrates each technique.
rapidly commence following denervation. Proteases play
[13]
a role by promoting axonal degeneration, macrophage SENSORY PROTECTION ‑ THREE
infiltration, and myelin degradation in damaged nerves. [14]
APPROACHES
Without prompt reinnervation, myofibril disorganization,
and later mosaic disappearance marks imminent muscle End‑to‑end neurorrhaphy
fiber cell death. Prolonged denervation leads to muscle End‑to‑end neurorrhaphy is the classic approach for
[15]
fiber necrosis, connective tissue hyperplasia, decreased sensory protection. Bain et al. demonstrated the positive
[9]
vascularity, and depletion of satellite cells needed for effects of sensory protection on the architecture and
regeneration. [4,9,16] Further, denervated muscles become
less receptive to regenerating motor axons due to the
loss of neurotransmitters, neurotrophic factors, and viable
muscle cells. [2,17] These structural changes significantly
impact the muscle’s contractile properties. The decrease
in cross‑sectional area of muscle fibers translates to a
reduction in maximum tension generated by tetanic muscle
contractions. Later on, myofibril disorganization and
collagenization diminishes specific force capacity (force a b
per physiological cross sectional unit of muscle). From a
functional perspective, maximum tension, specific force,
and power all progressively decrease with time. [13]
Nerve regeneration and muscle recovery
Regenerative processes occur synchronously with
degradative mechanisms to ensure maximal recovery.
Axonal regeneration occurs at a rate of 1 mm/day and c d
is affected by age, nerve type, and grade of injury. Figure 1: Schematic representation of surgical methods for sensory
[18]
Recovery involves axonal growth, synapse formation, and protection. (a) Transected nerve, denervated muscle without sensory
restoration of contractile properties. Schwann cells play protection; (b) sensory protection by end‑to‑end neurorrhaphy;
(c) sensory protection by end‑to‑side neurorrhaphy; (d) sensory
an essential role in regrowth by increasing regenerative protection by direct muscle neurotization
Plast Aesthet Res || Vol 2 || Issue 4 || Jul 15, 2015 203