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Spinal Stenosis

Adequate space within the spinal canal and the foramina (exiting channels for the nerves) is essential to ensure that the spinal cord and it's attached nerve roots can slide freely with spinal movements. Spinal stenosis is defined as reduction in the space available for the neural elements within the bony spinal canal.

The components that cause mechanical restriction within the canal can be the result of bony and/or soft tissue impingement. An example of bony impingement  would be osteophyte formation secondary to arthritic change.  Examples of soft tissue impingement would be from a protruding intravertebral disc and/or an enlarged ligament (primarily the ligamentum flavum) occurring as a result of degeneration.

If the neural elements are constricted for any reason, symptoms will result.

The symptoms and physical findings of spinal stenosis are distinctly different from those of a herniated disc:

	Spinal Stenosis	Herinated Disc
Pain	neurologic claudication (cramp-like pain and weakness in the legs, due to nerve root irritation, particularly with activity)	pain along the course of a nerve or it's roots into the lower extremity, accompanied by numbness, tingling, weakness, tenderness and loss of sensation
Relief	rest/bending forward	variable, extension, lying down
Locale	often bilateral; radiates to buttocks, groins, thighs and down legs	usually unilateral; radiates down leg to foot
Numbness	may be relieved by change in body position	unrelieved by change in body position
Motor Weakness	often absent; ‘heaviness' of both legs with use	possible motor weakness and loss of reflex(es)
Neural Tension Signs	none	positive (straight leg raise, tripod and bowstring signs)

Spinal stenosis may be due to congenital or acquired causes:

Congenital: the volume of the central tunnel of the spinal canal is determined by the height of the walls of the tunnel.  These walls are called pedicles.  If the pedicle height is smaller than average, the volume will be smaller than average, leading to primary congenital spinal stenosis.  There are also other conditions such as achondroplasia (dwarfism) which result in significant spinal stenosis.

Acquired: the facet joints connect the vertebral bodies.  They have to be aligned anatomically for optimal function (similar to car tires).  If optimal alignment is not present, increased joint wear will occur.  If an intravertebral disc (shock-absorber and spacer) loses height with age or injury, the facet joints may wear prematurely.  Both disc narrowing and facet arthritis will cause narrowing of the foramina where the nerve roots exit the spinal cord. Spinal stenosis may be secondary to degenerative scoliosis and/or spondylolisthesis. Iatrogenic causes (induced by treatment) may include lumbar fusion, particularly at the level above the fusion. Other causes include tumors and some metabolic disorders such as Paget's disease and acromegaly (pituitary gland hyperfunction resulting in excessive growth hormone production). These bone diseases cause increased deposition and decreased resorption resulting in excessive space-occupying bone formation.

Most cases of spinal stenosis reflect primarily a degenerative involvement.  If this is combined with a degree of primary (congenital) stenosis, symptoms may occur earlier in the course of arthritis, with fewer degenerative changes.

If symptoms are significant and investigations demonstrate the presence of spinal stenosis, conservative measures will often fail and surgical intervention may be required for appropriate management.

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