Principles of Nerve Repair Flashcards
The perineurium serves to bundle axons together to form fascicles and is a major contributor to peripheral nerve tensile strength
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Wallerian degeneration process begins within 24 to 48 hours of injury and involves complete axonal degeneration distal to the site of injury
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Wallerian degeneration halts at
the closest intact node of Ranvier, which also serves as the site of subsequent axonal growth
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dedifferentiated Schwann cells proliferate
along the residual endoneurial tubes and create columns known as
Bands of Biingner
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superior clinical outcomes are observed when endoneurial tube remains
intact
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Axonal regeneration occurs at a rate of approximately 1 to 3 cm/ day
F Axonal regeneration occurs at a rate of approximately 1 to 3 mm
per day or just slightly more than an inch per month
sensory end organs do
not undergo such degeneration and can be reinnervated many years
later with satisfactory results
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scarring can be present in third degree nerve injury
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include traction and iatrogenic
nerve injection can result in third degree nerve injury
F 4th degree
here is no diagnostic test to distinguish between second-, third-, and fourth-degree
injuries
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Fibrillations and positive sharp
waves (PSWs) on needle EMG indicate first -degree Sunderland injury
F Fibrillations and positive sharp
waves (PSWs) on needle EMG indicate axonal loss and therefore at
least second-degree Sunderland injury
PSWs can be observed as early as 3 weeks after nerve injury
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fibrillations are typically observed around 6 weeks after nerve injury
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The presence of fibrillations and PSWs on EMG are significant to
the prognosis why?
because they reveal that the distal motor plates in the
target muscle fibers are still available for reinnervation
The size,
shape, and recruitment pattern of motor unit potentials (MUPs) on
needle EMG is helpful in determining the duration of nerve injury
and the expected potential for functional recovery
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The reappearance of MUPs on
EMG about 12 weeks after injury represents second- and
third-degree Sunderland nerve injuries
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Electrodiagnostic studies may be obtained immediately after significant trauma
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The harvested nerve
graft undergoes Wallerian degeneration
t
nerve innervating a free muscle transfer can be considered as a possible graft
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The autograft should be placed in
reversed orientation at the repair site to prevent loss of regenerating
axons down side branches
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In nerve Allograftsthe recipient should receive immunosuppression for two years
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Conduit can lead to formation scar tissue
F The absorbable nature
of these conduits limits the associated foreign body reaction that can
result in scar tissue encapsulation and subsequent inhibition of axonal growth
Stem cells and Schwann cells seeded
into nerve conduits have demonstrated significantly better functional
outcomes compared with empty conduits
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these constructs have been shown to
support successful nerve regeneration across small diameter nerves
with gaps up to 3 cm or with large diameter nerves with gaps less than
0.5 cm.
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for motor defects or nerve defects that span more than
3 cm, autologous nerve grafting is still considered the standard of care
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When an end-to-end repair is planned,
the donor’s nerve is ideally transected as proximally as possible to
F When an end-to-end repair is planned,
the donor nerve is ideally transected as distally as possible and the
recipient nerve is transected as proximally as possible to optimize a
tension-free coaptation
In Younger patients, distal nerve repairs do better than proximal
repairs
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pure sensory or pure motor nerve repairs do
better than mixed nerve repairs
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, VTE, per se, is not a contraindication to free tissue transfer
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Topical
papaverine works by blocking sodium channels
F Topical
papaverine works by blocking calcium (not sodium) channels
Transcutaneous tissue oximetry can detect vascular compromise before clinical signs alter
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The use of systemic heparin increases
the risk of postoperative bleeding, but its action is short-lived compared with low molecular heparin
T
When functional connections are not made in a
timely fashion, axons can degenerate in a process known as pruning
T
Amplitude of the recorded CMAPs
provides an estimate of the number of intact motor axons activating
muscle fibers.
T
The reappearance of MUPs on
EMG about 12 weeks after injury reflects the collateral sprouting of
adjacent, uninjured nerve fibers and thus represents second- and
third-degree Sunderland nerve injuries
T
in
fourth- or fifth-degree Sunderland injuries, MUPs are not typically
seen on EMG because all of the axons have lost continuity with their
target muscle fibers.
T
Total division of a peripheral nerve may be better diagnosed
with imaging studies such as ultrasound or magnetic resonance
imaging.
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Medial antebrachial cutaneous nerve provides up to 20 cm of length and the LABC up to 8 cm
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motor
nerves grafts are thus reserved for instances where no sensory donors
are available and nerve transfers would not provide a better option
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Allografts can be decellularized to avoid the need for immunosuppression
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all alternatives to autologous nerve grafts, including
decellularized allografts and tissue-engineered conduits, demonstrate
similar efficacy in reconstruction of sensory nerve defects of less than
3 cm
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Synthetic nerve conduit reconstruction of nerve
has not proven effective in gaps longer than 2 cm and is less
effective in motor nerve defects.
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The LABC nerve is the distal continuation of the musculocutaneous nerve.
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Minimal tension and an increasing number of suture strands crossing the repair site are both associated with improved function.
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