Lumbar Spinal Stenosis (Spine)

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