Lumbar Spinal Stenosis

Epidemiology

  • Most common cause of spine surgery >60 years
  • Men > Women
  • Narrower canal between L3-L5

Aetiology

  • Acquired – common:
    • Degenerative – most common
    • Paget’s disease
    • Post-traumatic
  • Congenital – uncommon:
    • Acromegaly
    • Achondroplasia

Pathophysiology

  • Mechanical compression of neural elements within spine
  • Intraneural oedema
  • Release of pain mediators e.g., substance P

Anatomic Factors

  • Contributing structures:
    • Trefoil-shaped canal
    • Congenitally narrow canal
    • Bony changes:
      • Facet joint hypertrophy
      • Osteophyte formation
      • Subluxation/degenerative deformity
    • Soft tissue:
      • Ligamentum flavum hypertrophy
      • Disc herniation
      • Facet capsule hypertrophy

Location of Stenosis

  • Central or lateral (lateral recess, foraminal, extra-foraminal)

Central (common)

  • Within canal – anterior to flavum, posterior to PLL & medial to facet joint
  • Ligamentum flavum is main offender

Lateral Recess (less common)

  • Just before the foramina – medial to pedicle but lateral to thecal sac

Foraminal (less common)

  • Within the exit foramina – between pedicles & in front of facet joint
  • Facet joint hypertrophy is main offender
  • Normal foraminal height = 25 x 9 mm

Extra-foraminal (rare)

  • Impingement of L5 root between sacral ala and L5 TP
  • Related to scoliosis/spondylolisthesis
  • Diagnosed using 25-degree caudal CT/MRI (Ferguson view)

Diagnosis

History – Typical

  • Pain in buttocks and thighs radiating distally
  • Non-dermatomal
  • Proximal to distal in onset
  • Numbness
  • Rarely, weakness or bladder disturbance (late)
  • Related to standing or walking
  • Relieved by sitting or lying down
  • Easier with spine flexed:
    • In extension, ligamentum flavum buckles into canal
    • Shopping trolley, uphill & up stairs easier

Examination

  • Usually normal including neurology & neural tension tests
  • Extension test positive
  • Treadmill test 90% sensitive
  • Bicycle test
  • Always rule out other causes:
    • PVD, malignancy, disc herniation

Imaging

  • XR as baseline
  • MRI/CT myelogram:
    • Gold standard
    • Look carefully for foraminal & lateral recess stenosis

Management

  • Natural history is to improve in 30% with time
  • Steroids, NSAIDs & physio do not alter natural history

Surgery

  • Commonly performed
  • Laminectomy with decompression of flavum and medial aspect facets
    • Undercutting of facets to decompress lateral recess & foramina
  • Fusion only needed if:
    • Wide decompression over multiple levels
    • Segmental instability
    • Degenerative scoliosis – in a younger patient
      • Degenerative scoliosis/spondylolisthesis in elderly tends not to be progressive even after surgery

Results

  • Surgery has better short & medium-term results than non-operative
  • Good for pain relief – may leave numbness
  • Results decline as degeneration continues

Poor Indicators of Outcome

  • Multiple co-morbidities
  • Single-level surgery
  • Long operative time
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