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The challenges involved are a matter of statistical probability. This
represents the risk of surgery and not that of bad practice as long
as it is not accompanied by negligence or unjustified deviation from
a reasonable standard of care.
Clearly the less diligent and less experienced spine surgeon will
encounter complications more
frequently. The risks of nerve injury are clearly higher if the
patient has had previous surgery in the same area. It is
important to point out that skilled spine surgeons, dealing with
complex cases, can achieve lower complication rates than those seen
on simpler cases.
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| This above is a portion of a letter received
from a 37 year old patient from England who had undergone one previous
surgery without clinical improvement. While this patient's operative
risks would certainly be higher than normal one wonders why the patient
could not have been referred to a surgeon with greater experience and
skill. Unfortunately for the patient the reason why this did not
happen should be apparent to the viewer.
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The nature of nerve injuries,
should they occur, is a very important subject.
The human nervous
system is truly remarkable in its ability to deal with insult and
injury. Its truly astonishing neuronal reserve and redundancy act
effectively to continue to protect our ability to maintain
function. This is particularly true when we are young
and the system is
most plastic. |
The ability of nerves to tolerate insult and injury varies.
Some, such as the sacral spinal nerves supplying bowel, bladder,
and reproductive function have poor recovery potentials. The somatic nerves supplying
motor and sensory function are a much more rugged great deal.
The illustration above is a schematic depiction of the nerve
supply zones in the human body. These normally
overlap in their coverage, particularly in regard to somatic
function (please see figure A). Should total nerve supply be suddenly
interrupted (as when a nerve avulsion occurs), as illustrated by
removal of the brown circle (please see figure B) an immediate deficit in neurologic function is
created.
Our brains (our master computers)
constantly are bombarded by a stream of constant and complex
incoming (afferent) information from a myriad of
sources. When this is suddenly "turned off" from a
otherwise continuing nerve "stream" (termed "deafferentation")
the brain has to figure out how to deal with this sudden
deficit. When somatic nerve injury
occurs associated with complete cessation of input (afferent) information the nervous system immediately starts
the process of
recovery. Should an entire extremity be off the brain
typically then perceives a "phantom limb" as the
echo of previous
afferentation continues to reverberate in the system. Unless
this "phantom" is reinforced by other input, such as pain, the phantoms gradually subside and
disappear.
When the loss of afferentation is not so great, i.e. if only a single, predominantly motor and
sensory nerve, is completely cut or avulsed the remaining
functioning adjacent nerve zones begin to extend their
coverage to the area of impairment (the missing brown circle)
allowing the individual to progressively recover and often return
to what a appears to be a total recovery but is, in fact a
"tour de force" demonstration by our bodies (please see
figure C). The "reafferentiation" phenomenon
which is occurring
is something which can be
enhanced (see below). The process
of recovery may also involve some nerve
regeneration. This is usually complete within 2 years.
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| The Incomplete
Nerve Injury |
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In the illustration
to the left the nerve supply to the brown circle area has only
been incompletely (partially) eliminated. This is a
bad situation because the human nervous system is usually not able to
deal with this in an effective manner for the individual. In
this case the partially injured nerve continues to sent
information to the brain which is incomplete. It is
always better to have a complete nerve termination rather than an
incomplete injury. |
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Because of
this the brain thus has great difficulty in recognizing
the pattern and usually interprets the input as a most disagreeable, constant
sensation better described as "agony" rather than
pain. Dr. Weir Mitchell identified this highly disagreeable
sensation, frequently observed in soldiers with peripheral nerve
injuries during the American Civil War, and coined the term "causalgia"
to describe it.
When partial deafferentation occurs the adjacent nerve supply
zones do not appear to recognize that they need to lend "a
helping hand." If autonomic nerve elements or
vascular components are involved another entity referred to as
"reflex sympathetic dystrophy" (RSD) may occur.
"Reflex sympathetic dystrophy"
and causalgia often exist together. The difficulty in sorting these
out has led pain specialists ("dolorologists") to introduce the
term "regional complex pain disorder" (RCPD) as a generic description
of these types of pain (agony). The treatment of the RCPD entities
remains one of the most difficult know to medicine today.
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| Avoiding Causalgia By
Purposeful Nerve Section |
The role of the physician and surgeon is to do whatever is in the best
interests of their patient. This sometimes means taking action to
avoid life-time disabling problems such as causalgia. Such a
situation is presented below in the case of a middle-aged individual
incapacitated by right leg pain over a period of years. Imaging
studies showed a Grade 1 lytic spondylolisthesis at the L5-S1 level.
There was severe lateral spinal stenosis. The exiting L5 nerve was
markedly attenuated, compromised and stretched (see red dot). The
surgeon felt that the decompression had added further insult to this
thinned nerve and sectioned it. A single posterior titanium cage
was inserted and strut created to serve
as a "shock absorber" to protect the superior discs.
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Following surgery this patient was relieved of all leg pain and
demonstrated normal neurologic function. It is clear that in the
process of progressive nerve impairment neurologic function had been
transferred to the adjacent segments. |
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| Managing Spinal Nerve Injuries |
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There are a number of therapies, which, if
appropriately applied, can greatly assist in the recovery from nerve
injury when it does occur:
Medications:
Tricyclic drugs (i.e. elavil, sinequan, etc.) and
neuronal metabolic enhancers such as gabapenta (Neurontin®)
are often worthy of consideration. Narcotic medications are a mixed
blessing because of their serious side efftects.
Reafferentation:
Massage
Vibration
Transcutaneous Electrical Nerve Stimulation (TENS)
Heat-Cold Application
Exercise
Neurostimulation:
When all other treatment modalities
fail the implantation of a electronic pain relief
device needs to be considered. |
Summary |
Nerve injury at surgery is always an
unfortunate event. Even surgeons with the greatest skill and
experience can experience this. The disability and incapacitation
experienced by patients is always less following complete, rather than
partial, nerve section. There are, however, effective means of
managing such problems. In addition to the injury of isolated nerves
other forms of nerve injury i.e. spinal cord, conus medullarus, and cauda
equina are possible. |
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