Nerve
injuries should be approached aggressively in open injuries, as there is
never a better time to evaluate and to perform repairs. In the context
of an adjacent open wound, nerve dysfunction should be considered an open
nerve injury until proven otherwise. Partial nerve lacerations are clearly
best treated by early repair. If untreated, the nerve heals with a large
neuroma, and partial function returns. If such an injury is explored late,
it may be impossible to distinguish neuroma from scarred nerve fibers in
continuity, and the surgeon may face the no-win choice of either leaving
things as they are or performing a segmental complete nerve excision and
grafting, possibly leaving the patient worse off than they were prior to
surgery.
If
a nerve appears injured, but is not explored, nerve studies may not be
helpful in distinguishing neuropraxia from more severe nerve injury for
several weeks. At that point, conditions may not be favorable for nerve
exploration, and it may be reasonable to wait for nerve recovery, assuming
that the nerve is injured but in continuity. How long is it reasonable
to wait before expecting to see signs of muscle recovery following an in
continuity injury? This can be calculated, making a few assumptions: 1)
Muscle recovery is poor if motor point reinnervation is delayed past 12
months, and unlikely if delayed past 18 months; 2) Following repair, axon
growth proceeds at an average of 30 millimeters per month; 3) That the
probable site of the nerve injury is known; 4) That there is no other evidence
contrary to the diagnosis of a closed stretch injury. If these assumptions
apply, it should be "safe" to wait for distal muscle to s how signs of
reinnervation for a period of 12 months minus (distance in millimeters
from injury to motor end point divided by 30 mm per month), or 12 - (distance/30)
months. Within that time frame, recovery could still be anticipated even
if delayed excision and repair is performed. So, for example, in an ulnar
nerve injury, if the distance from a forearm injury to the first dorsal
interosseous muscle along the course of the ulnar nerve was 180 millimeters,
it would be "safe" to wait up to (12 - 180/30 =) six months before the
window of opportunity for surgical success began to close.
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