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Lateral Spinal Stenosis


In 1981, a International Study carried out to determine the anatomical reasons behind failed back surgery found that the  the most common reason for a bad surgical result was failure of the surgeon to either identify or adequately treat the entity know as "lateral spinal stenosis" (LSS). 

The primary researchers behind the 1981 study continued to monitor the failed back surgery situation and, even at the year 2000, the start of a new millennium, they concluded that LSS continued to be the primary reason for surgical failure.  Sadly, this situation continues to be true.  The reasons behind this astonishing observation are difficult to comprehend because such a high failure rate would not be tolerated in any other surgical specialty. 

Because of the importance of this subject Burton Report has been focused on attempting to better inform physicians and patients and make them more aware of the need for more specific diagnosis and more appropriate surgical therapy based on this information.  Surgeons and their patients need to reflect on the observation that "there is no such thing as a non-specific patient, there are, however, non-specific surgeons." This observation is eminently applicable to spine surgery and spine surgeons.   

The term "foramen" means whole or opening.  In regard to the spine it refers to the openings through which spinal nerves and their associated arteries and veins depart from the bony spinal column.  Lateral spinal stenosis was first described in 1940 by neurosurgeon Henk Verbiest

The location of these foramina are demonstrated in the drawings below:
           

This normal axial anatomic specimen provided by Wolfgang Rauschning shows the relationship of the spinal canal to the lateral foramina.  The vertebral body is below the spinal canal and the lamina and dorsal process are above.
   
     SPINAL CANAL ZONES
This illustration demonstrates, in axial and coronal planes the central, (C) foraminal (F), and extraforaminal (E) zones of the spinal column. It is important to recognize that this drawing represents normal anatomy.  Most individuals undergoing diagnostic evaluation and surgery do not have "normal" anatomy and that is the very reason that they are requiring medical evaluation and treatment   
This illustration of normal anatomy also shows the Central, Foraminal, and Extraforaminal zones but also includes the exiting spinal nerves.  Attention needs to be directed to the dorsal nerve root ganglion (shown in yellow) which lies in the Foraminal zone.
It is the compression of the dorsal root ganglia with associated impairment of  venous return which causes swelling of this structure and associated nociception which creates the clinical perception of associated pain.  In fact, the dorsal nerve root is the primary pain generator when nerve roots are compromised.
The drawing above, published by Leon Wiltse shows a critically important modification from normal.  Note that the facet joints have begun to enlarge and have narrowed the lateral aspects of the Central Canal zone.  Wiltse has identified this area as the nerve "Entrance Zone."  Others have designated this area as the "Subarticular Recess" or the "Lateral Recess."  This location is often confused by surgeons as being the same as the Foraminal Zone (which it is not) leading to their performing inadequate decompression leading to failed back surgery.
 
The next illustration to the left shows the effect of  progressively enlarging facet joints.  The recesses of the Central Canal zone have been closed down and the exiting spinal nerves are being compressed.  The beginning of the Foraminal zones are indicated by the red dots.
The case on the left shows an example of severe nerve compression on the left side involving the central (blue), foraminal (green), and extra-foraminal (red) zones.  The image is in the same orientation as the drawing above.
A spine surgeon intending to relieve lateral spinal stenosis would need to decompress lateral to the red dot.  If the decompression were limited to the Central Canal zone only the nerves in the recess would have been helped by the surgery.  This drawing shows an example of central spinal stenosis where bulging of the intervertebral disc has also added to the central nerve compression.  Complex cases of multiple nerve compression such as this are characteristic of genomic spine disorders and typically require more than a rigid fusion with pedicle screws and rods.
 

A classic example of failed back surgery due to confusion regarding the site of nerve compression is shown here.  This 78 year old executive had 2 surgical decompressions to relieve lateral spinal stenosis.  The only  decompression was of the Central Canal zone and not the Lateral zone (see red dot). 
This patient's problems were further complicated by a persistent post-operative cerebrospinal fluid leak producing a pseudomeningocoele and a large spinal fluid filled subcutaneous sac.
 
  The Many Forms Of Lateral Spinal Stenosis   

The variations on the theme of "lateral spinal stenosis" are endless.  The combinations of disc and annular protrusion, facet hypertrophy, and spur formation are also endless.  It has been valuable however, to attempt to classify these entities and shown below is one schema developed by neurosurgeon Charles D. Ray.  It references the "hard" tissue patterns identifiable on high quality MRI scans.
 

Courtesy Charles D. Ray

Of all of the lateral spinal stenosis patterns, that of the Superior Articular Facet (SAF) syndrome has been the most elusive to diagnose because it requires a more sophisticates high resolution MRI scan to identify it as well as a radiologist and clinician who even know that it exists.
 

How Is It That Spinal Can Nerves Be Compressed And
Still Function Normally?   


 

Courtesy Wesley Parke    

1- Fascicular Pia-Arachnoid
7- Radicular Pia-Arachnoid
3- Major Radicular Longitudinal Artery
6- Collateral Radicular Arteries
2- Intra- and Interfascular Arterial Coils
4- Radicular Vein
5- Arterio-Venous Anastemoses

Professor Wesley Parke has well demonstrated that impairment of venous return is the primary reason that compressed nerves become pain generators. These spinal nerves become symptomatic when their nutrient supply is cut off and their venous return is impaired.   The vascular anatomy of a typical spinal nerve is shown above and to the left.  The ability of the human body to acclimate to gradually applied insult is the stuff of legend.  A markedly constricted (75% of original size) S1 dorsal nerve root is shown to the left above.  This patient had a 5 year history of "neuroischemic claudication" but was ambulatory at the time of his death from congestive heart failure.  Post mortem study showed a preservation of the longitudinal radicular arteries, but obstruction of the draining veins.  It is important to point out that any sudden change imposed on this typically quiescent, but marginal situation, can produce acute  incapacitation and disability in a patient.
 

The reason as to why the leading cause of failed back surgery remains failure to adequately diagnose or treat lateral spinal stenosis makes clear that many spine surgeons continue to be ignorant of basic spine pathology.  As noted above, the most common error performed by surgeons is to mistake the narrowing of the lateral Central Canal zone as being the same as the Foraminal zone and only performing a central decompressive laminectomy. 

This error in judgment has produced legions of patients with continued disability.  When "salvage" surgery is then attempted the patient risks increase.  In the case shown below the patient's disability was due to multi-level lateral spinal stenosis. The first surgery was only a central decompression (not involving the Foraminal zone) and did not accomplish it's intended result.  The second surgery, in this case, only compounded the error by performing a multi-level instrumented fusion and still not addressing the real culprit, continued nerve compression due to continuing lateral spinal stenosis.  An additional liability for the patient is all of the hardware in their spines making MRI, the diagnostic procedure of choice, more difficult to accomplish because of associated metal artifacts.  The patient may also need additional surgery in time to remove the hardware.  Can there be any question but that better surgical planning and procedures are needed?
      


The two images below illustrate a not uncommon situation where multiple surgeries have been performed specifically for the purpose of relieving nerve compression secondary to lateral spinal stenosis without actually accomplishing it.  In this patient with scoliosis L5-S1 nerve compression secondary to lateral spinal stenosis has occurred (red dot) due to axial loading and prominent bone spur formation.  A coronal view (to the right) shows an still uncompressed and swollen L5 nerve (red dot on nerve).  Compare this to the normal L5 nerve on the opposite side.  Despite 3 previous operative failures the 4th procedure (salvage) did indeed adequately decompress the nerve and allow the patient satisfactory relief of disability.
       


The series of photos above and below relate to a 52 year old steel worker with low back and bilateral leg pain related to a Grade 1 isthmic spondylolisthesis and bilateral lateral spinal stenosis.  The first operative procedure was the anterior placement of two titanium cages.  No decompression of lateral spinal stenosis was performed and the patient's leg pain continued.  The second operative procedure was to remove the titanium cages from an anterior approach and perform a posterior instrumented fusion, again without nerve decompression.
 
               

Because of the patients continued leg pain he was then referred to a "pain clinic" where, after a number of injections, he was then placed on strong narcotic medications.  The next step was the placement of a percutaneously inserted neurostimulating system by an anesthesiologist.  This required multiple revisions and provided poor pain relief.  Following all of these surgeries and procedures this patient was an even more  incapacitated individual with a chronic pain syndrome, requiring significant narcotic drugs, and having a very poor chance of meaningful rehabilitation.  Present medical treatment made this patient worse off than he was to start with.  His lateral spinal stenosis was never corrected.

Even when a surgeon is aware that lateral spinal stenosis exists and performs what is believed to be an adequate decompression this act alone does not necessarily restore integrity to the nerve or its venous return and continued clinical impairment may result.  Adequate surgical decompression of an impaired spinal nerve must allow it to be be "balgreat dealtable" in order to assure the best possible result for the patient.

The basic tenant of the Hippocratic Oath is "do no harm."  Shown above are examples of continued lateral spinal stenosis because of inadequate diagnosis and inadequate surgeries which did not effectively address the initial problem.