October 2017 Edition. Volume XVII

“If you haven’t avulsed a nerve root you just haven’t done enough spine surgery”

Frank Otenasek M.D.  (Baltimore Neurosurgeon, quoted in 1965)

Frank Otenasek

Frank Otenasek

This observation means that even the most diligent and experienced spine surgeon will, in time, experience serious complications, such as nerve injury.  This may be a human factor, it may also relate to the complexity of the case including the presence of unsuspected abnormal anatomy such as a conjoined nerve root or extensive post-surgical scar tissue from previous operative procedures.

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.

EnglandFBSSLet600GIF

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.

Spinal Nerve Injuries

NerveInj200GIFThe 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.

The Incomplete Nerve Injury

NerveCaus200GIFIn 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.

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.

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.

SPONDSEVLSS_Lat200JPG  SPONDSEVLSS_For200JPG  SPONDSEVLSS_Cg200JPG

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.

Managing Spinal Nerve Injuries

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 effects.

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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