Description:
Any developmental of acquired narrowing of the spinal canal, nerve root canals, or intervertebral foramina that results in compression of neural elements

Pathophysiology:

  • A small amount of canal narrowing occurs with age
  • The narrowest part of the canal is L2 – L4
  • Volume increases in flexion and decreases in extension
  • Causes of pathologic narrowing of the canal include:
  • Bulging of intervertebral discs posteriorly
  • Buckling of the ligamentum flavum posteriorly
  • Encroachment of the articular facets
  • Degenerative spondylolisthesis
  • Mechanical compression of cord results in increasing pressure in stenotic canal and:
  • “neuroischemia” – nerve fibers are nutritionally deprived by compression of small vessels
  • Inflammation of dura and exiting nerve roots results in adhesive arachnoiditis of the pia and friction neuritis which constricts and tethers neural elements
  • Reduced permeability of hypertrophic restricts CSF flow, which provides 50% of nutrition to nerve fibers
  • Pain and paresthesias are produced when activity increases the metabolic demands of nerve fibers beyond what the limited delivery of nutrients and removal of noxious substances allows

Classification:

  • Congenital
  • Example, achondroplasia
  • Acquired – more common
  • Degenerative
  • Olisthetic-scoliotic
  • Post-traumatic
  • Post-operative
  • Location of stenosis
  • Central – hypertrophied structures put circumferential pressure around spinal cord
  • Lateral – associated with narrowing of the foraminal canal


Signs/Symptoms of Degenerative Spinal Stenosis:

  • Most common in elderly
  • Women > Men
  • Lower lumbar segments
  • Insidious progression of lower back, buttock, thigh pain
  • Lower extremity pain that is altered by position, relieved by rest – especially a position of flexion of the waist
  • Can ambulate longer pushing a shopping cart (flexed body position)
  • Distal pulses should be evaluated to distinguish claudication from neuroclaudication

Imaging:

  • Plain radiographs demonstrate
  • degenerative disc disease
  • osteoarthritis of facets
  • spondylolisthesis
  • narrowing of interpedicular distance on AP
  • CT scan allows for accurate measurement of canal dimensions
  • Dural sac with diameter of less than 10mm correlates with clinical findings of stenosis
  • MRI is now imaging modality of choice, comparable to contrast enhanced CT

Differential Diagnosis:

  • Causes of referred pain to lower back:
  • Retroperitoneal tumors
  • Aortic aneurysms
  • Peptic ulcer disease
  • Renal lesions
  • Hip and pelvis pathology
  • Psychologic causes of low back pain
  • Depression – common in elderly

Typical midline decompression for spinal stenosis

Treatment:

  • Non-steroidal anti-inflammatory medications
  • Exercise program
  • Many patients have appreciable response to NSAIDS and exercise
  • Narcotics should be avoided
  • Epidural corticosteroid injections have short-term success rate of 50% and long-term 25%
  • Decompressive laminectomy has short-term success rate between 71-85%
  • Reoperation common due to instability or recurrent stenosis
  • Disc should be preserved for stability
  • Prophylactic instrumented fusion should be performed if decompression will involve bilateral facet resection