Spinal Stenosis

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Introduction

Narrowing or stricture of the spinal canal causing neurological symptoms or dysfunction

Anatomy

  • The cross sectional shape of the spinal canal has been classified into three shapes:
    • Round
    • Ovoid
    • Trefoil
  • The AP diameter
    • Measured from the posterior vertebral wall to the upper border of the spinous process
    • The mean AP diameter of the spinal canal is 12 mm
  • Cross sectional area
    • Minimal cross sectional area is normally at the level of the facet joints
    • The narrowest cross sectional area is at the level of L3/L4
    • Men have narrower spinal canals at the L3 - L5 levels
    • Canal area of 180 mm2 ± 50 mm2 is normal in the lumbar spine
      • < 100 mm2 is spinal canal stenosis
      • 100 - 130 mm2 is early or relative canal stenosis
  • The normal interpedicular distance should be ? 16 mm
    • < 10 mm : Absolute stenosis
    • < 12 mm : Relative stenosis
  • The lateral canal usually measures 5 mm
    • < 2 mm indicates stenosis
  • Radiologic definition of stenosis in cervical region
    • < 13 mm AP diameter, or
    • < 0.8 times the AP diameter of the adjacent vertebral body
  • Central canal stenosis may be exaggerated by
    • Hypertrophy of ligamentum flavum
    • Hypertrophy and osteophyte formation of the facet joints
    • Annular bulging of the disc
    • Thickening of the lamina
  • Lateral recess stenosis can result from
    • Loss of disc height and over-riding facets
    • Facet joint osteophyte formation
    • Hypertrophy of ligamentum flavum / capsule of the joint
    • Posterior annular bulge
    • Extradural arachnoid cysts
    • Perineural cysts
  • Arrangements of nerve roots within the thecal sac
    • The most posterior roots are always the 5th sacral roots
    • The other roots are added progressively toward anterior
    • At the L5-S1 disc level, the most anterior nerve root is the S1 nerve root
    • Motor fibres are antero-medial within the roots and the sensory fibres postero-lateral
    • The dorsal root ganglion lies in the neuroforamen, with a small motor component anteriorly and a larger sensory component posteriorly 
  • Blood supply of the cauda equina
  • The blood supply of the cauda equina and spinal nerve roots is from cephalad to caudad
  • As the nerve root traverses the neuroforamen the blood supply is from caudad to cephalad 

Pathogenesis

The commonest cause in the elderly (esp. females) is degenerative L4/L5 spondylolisthesis

Pathoanatomy of disc degeneration

  • The intervertebral discs are fibro-cartilaginous structures that separate vertebral bodies and provide shock absorbance within the intervertebral joint
  • The annulus fibrosis is composed of 50% type I collagen and 50% type II collagen
  • The nucleus pulposus is comprised exclusively of type II fibres
  • With aging process the water content of the intervertebral discs decreases
  • The proteoglycan content is replaced by collagen fibers
  • The precise molecular mechanism that underlie this process is not known
  • Dehydration of the nucleus pulposus decreases its ability to distribute stress and consequently
    • Fissures and tears develop within the annulus
    • The discs lose height
    • Annular bulges develop
    • Disc herniates
  • These changes increase stresses on the facet joints, which causes
    • Arthritic changes
    • Osteophyte formation
    • Sclerosis of the endplates
    • Occasionally, instability
  • Ligamentum flavum, which is normally elastic, hypertrophies and becomes more rigid
  • Hypertrophic changes result in narrowing of the spinal canal and neuronal foramina
    • Compress the cord and nerve roots
    • The vasculature can also be compromised, resulting in ischemia

Pathophysiology

  • Compression
    • Does not cause pain per se
    • It will result in paraesthesias, sensory deficits, motor loss and reflex abnormalities
    • Affects the afferent fibres first, while recovery is quickest in the efferent (motor) fibres
  • Local neural inflammation
    • Produces the pain
    • Inflammation may be caused by stretching of the nerve
      • In a normal person, the S1 nerve root may move as much as 5 mm within the neuroforamen upon straight leg raising
      • Degeneration may prevent movement of the nerve and cause increased internal tension and disruptions of neural architecture
  • Possibly, vascular steal or venous congestion / stasis is involved in pathophysiology

Nutritional factors

  • Ameliorating factors may decrease symptoms of spinal stenosis
    • Proper hydration
    • Eating fruits and vegetables
  • Aggravating factors which have been proposed to induce inflammation and oxidative damage
    • Smoking
    • Alcohol
      • Increases the risk of falling, which can aggravate symptoms of spinal stenosis
      • Does not affect the risk of developing stenosis per se
    • Caffeine
    • Red meat
  • Definitive data supporting these measures is currently lacking

Natural History

Epidemiology

  • Incidence
    • 1.5 - 6% of population
    • 0.5% of Americans over 50 years old (250,000 - 500,000)
    • Incidence is expected to increase as the population gets older
  • M=F
  • Usually over 50 years old
    • Mean age for women is 73, slightly less for men
    • Occurs earlier in achondroplastics (around 40)
  • Does not seem to have a clear correlation with any specific race or body type

Prognosis

  • In absence of instability, the course of disease is fairly stable
    • Severe debilitating neurological deterioration in patients who have been managed non-operatively is rare
    • Complete resolution of symptoms is also rare
  • If left untreated, the symptoms of unstable spinal stenosis become progressively worse
    • Leg weakness can progress to complete loss of functionality and inability to ambulate
    • Loss of sensation in the lower extremities can lead to increased propensity to fall, leading to increased fracture risk
    • Eventually, loss of bowel and bladder function and loss of sexual function may occur

Clinical Presentation

History

  • Symptoms usually do not develop until the seventh decade
  • The early symptoms are often insidious in onset
  • Vague complaints of low back pain and stiffness are often the initial symptoms
  • Most commonly affects the 3rd, 4th and 5th motion segments of the lumbar spine
  • May have previous history of disc prolapse or chronic backache
  • Sudden worsening suggests disc prolapse or other acute decrease in volume of the spinal canal
  • Urinary dysfunction is uncommon
    • Only in severe cases, as part of cauda equina syndrome
    • Takes the form of urinary retention and subsequent overflow incontinence
    • Associated with sexual dysfunction 
  • Back pain
    • Aggravated by
      • Standing
      • Walking down hills
      • Extension of the lumbar spine
      • Men are often unable to stand up straight to shave
    • Relieved by
      • Sitting
      • Squatting
      • Lying down
      • Walking up hills
      • Flexing the spine
    • The ability of positioning to exacerbate or relieve symptoms is highly specific for spinal stenosis (93%) and helps to differentiate it from peripheral vascular disease
  • Radicular pain
    • Found in 20%
      • 50% of patients have double root involvement
      • 30% have single root involvement
      • 15% have triple root involvement
    • Pain characteristics
      • Exertional aching, heaviness, numbness, burning ± paraesthesia
      • Usually involves the entire lower leg, rather than only the thigh or the calf
      • Unilateral (root canal stenosis) / asymmetric bilateral (spinal canal stenosis)
      • May vary from side to side and from day to day
      • Not present at rest
    • More common in patients with severe foraminal and lateral recess stenosis
    • Corresponds to the L5 nerve root in almost 90% of cases
    • S1 root is involved in around 60% of cases

Examination

  • Loss of lumbar lordosis is typical
  • May reveal neurological deficit, but frequently normal
  • Most common neurological abnormality is weakness in the L5 distribution
  • Straight leg test and other root tension signs are characteristically negative
  • Stress neurological test : symptoms can be induced / worsened by getting the patient to walk first, until the pain is felt
  • Symmetrical loss of knee and ankle jerks can be a normal part of aging, but asymmetrical loss of reflexes is significant 

Differential diagnosis

  • Lumbar spondylosis
  • Vascular claudication
    • Pain is maximal in thighs rather than the calves
    • Associated with paraesthesia and weakness after walking
    • Stopping and keeping the back extended will not relieve the pain
    • Relieved fairly promptly by sitting
    • Walking with back flexed increases the walking distance; e.g. pushing shopping trolley
    • Skin changes and decreased pulses may be found on examination
  • Neurogenic pain
    • Peripheral neuropathy
      • Pain occurs in a glove and stocking pattern rather than a radicular pattern
      • Not positional
    • Diabetic amyotrophy : Characteristically affects femoral nerve
    • Motor neuron disease
  • Nearby joint pathology
    • Sacroiliac joint
    • Hip
    • Knee
  • Vascular
    • Abdominal aortic aneurysm
    • Spinal cord vascular malformations
  • Inflammatory conditions
    • Chronic inflammatory demyelinating polyneuropathy
    • Sarcoidosis
    • CMV
    • HSV
    • VZV
    • Lyme
  • Congenital tethered cord syndrome
  • Renal disease
  • Depression
  • Compensation issues 

Imaging and Diagnostic Studies

  • Symptoms doesn't necessarily correlate with the magnitude of compression on imaging studies
  • Patients can have radiologically significant stenosis without symptoms

X-Ray

  • Neither sensitive nor specific
  • May show
    • Short pedicles
    • Narrow interpedicular distance
    • Degenerative changes
    • Spondylolisthesis
    • End plate sclerosis
  • Flexion and Extension views should be taken to reveal instability

CT Scan

  • If CT scan is used it should be combined with a myelogram

Myelography

  • Usually combined with CT
  • Use a water soluble non-ionic contrast; e.g. Metrizamide or Iopamidol
  • High sensitivity and specificity for the anatomical condition (not for the presence of symptoms)
  • Provides a better view of the bony structures
  • Can be used to assess canal narrowing and osteophyte deposition
  • One study concluded that post CT Myelogram provides more useful information than MRI, but there are side effects to consider, such as headaches, meningitis and abscesses
  • Since it is invasive, MRI is generally preferred
  • Complications
    • 20 - 30% headache
    • 30% nausea 
    • Seizures may occur, if contrast gets around the base of skull or brain
    • Anaphylaxis
      • Rare 
      • Usually occurs when IV contrasts used (less so in CSF)
    • Myelography in the presence of a complete block may precipitate local oedema and inflammation with neurological deterioration

MRI

  • The best test for diagnosis of lumbar spinal stenosis
  • Allows visualization of
    • Spinal cord and nerve roots
    • Bony and soft tissue structures surrounding them
    • The best view of neural compression in a narrowed canal
    • Disc alignment
    • Ligamentum flavum hypertrophy
  • Reveals the cross sectional diameter of the canal
  • A myelogram-like picture of the CSF column can be obtained
  • It is both highly sensitive (>70%) and specific for the anatomical diagnosis of the condition, although it is not specific for the presence of symptoms
  • Because MRI is so sensitive for spinal stenosis, incidental stenosis is often found in asymptomatic patients taking MRI for other conditions

Electromyography

  • EMG can be used to support the diagnosis of lumbar spinal stenosis
  • Particularly helpful when incidental stenosis is found by MRI in the absence of clinical symptoms
  • Very sensitive for diagnosing symptomatic stenosis, demonstrated by decreased signal on EMG
  • It has a high negative predictive value for symptomatic stenosis in those with radiographic evidence
  • Not specific, as decreased signal by EMG can also be caused by other conditions that may or may not co-exist with lumbar spinal stenosis, such as polyneuropathy

Laboratory

  • Blood work is used to exclude other pathology
  • CBC
  • ESR 
  • Serum protein electrophoresis
  • Acid phosphatise
  • PSA

Classification

  • Congenital
    • Achondroplasia
    • Hypochondroplasia
    • Osteopetrosis
    • Idiopathic
  • Acquired : Often superimposed on a congenitally narrow spinal canal
    • Degenerative
      • Central
      • Lateral recess
      • Foraminal
      • Degenerative spondylolisthesis
    • Spondylolytic
      • Iatrogenic
      • Post laminectomy
      • Post arthrodesis
      • Post discectomy
    • Traumatic
  • Miscellaneous
    • Paget's disease
    • Acromegaly
    • Spinal tumours
    • Infection / TB
    • Fluorosis
    • Ankylosing spondylitis
  • Combined

Treatment

Quality of life remains the key determinant in deciding when to proceed with additional assessment and consideration of surgery

Non operative treatment

  • Education
  • Reassurance
  • Posturing
  • Exercise
    • Aerobic conditioning
      • Improves overall muscle tone
      • Improves truncal balance and posture
      • Reduces weight
      • Improves water balance
      • Decreases inflammation
    • Stationary bicycle is particularly recommended
  • Physical therapy
    • Includes flexibility training and posture adjustment
    • Can decrease symptoms, although there is little evidence to support its benefit
    • There is no standard therapy regimen
  • NSAIDs
  • Tricyclic antidepressants
  • Epidural steroid injection
    • Short-term symptomatic improvement
    • There is no level 1 evidence for long-term benefit
    • May be particularly effective in patients with predominant lower limb symptoms
  • Brace
    • Prescribed for short term use in patients with instability
    • Long term use of a brace can lead to truncal deconditioning and is not encouraged 

Surgical treatment

  • Emphasize to the patient that the operation is designed to relieve pain in the legs, not the back
  • Spinal stenosis surgery is the most common lumbar surgery in adults over 65 years old
    • Complex fusion surgery increasing in frequency
    • Simple decompressive surgery decreasing in frequency
  • Surgery indicated for :
    • Cauda Equina syndrome
    • Progression of neurological findings
    • Inability to walk, due to severity of weakness / pain
  • Decompressive laminectomy with nerve root decompression
    • Currently, the treatment of choice
    • Good for relieving leg pain
    • May not improve the back pain
    • Usually through a posterior midline approach
    • Assess decompression by passing an angled dural elevator around the nerve
    • The decompression should include all the levels that were involved on the MRI scan, not just the levels where there is neurological dysfunction
    • May increase instability problems with the occasional need for spinal fusion
  • Arthrodesis
    • May be required for instability
    • Indications for arthrodesis
      • Spondylolisthesis
      • Pre-existing scoliosis / kyphosis
      • Loss of lumbar lordosis; such that the patient has lost sagittal balance
      • A major component of symptoms is back pain
    • Indications for addition of instrumentation
      • Correction or stabilization of scoliosis or kyphosis
      • Arthrodesis of two or more motion segments
      • Recurrent spinal stenosis with iatrogenic spondylolisthesis
      • Spinal instability
        • Translation > 4 mm, or
        • >3 mm of motion between vertebrae on dynamic views, or
        • >10 degrees of angular motion
    • If there is no instability, arthrodesis will not improve outcome
      • Exclude segmental instability in the AP and ML planes on dynamic X-Rays
      • Avoid creating instability during decompression :
        • Maintain at least 50% of facets
        • Maintain at least 5 mm of pars
  • Interspinous spacer implantation
    • Effective at reducing disability up to 4 years after device placement
    • Its outcome has not been compared with standard laminectomy

Outcome

Non-operative treatment

  • Sufficient randomized clinical trial data investigating the efficacy of specific non-surgical approaches is currently lacking
  • Epidural steroid injections
    • Found to be effective at relieving leg pain for weeks to months
    • No proven effect on functional outcomes or need for surgery at 1 year

Surgery

  • Generally, good / excellent results can be expected for relief of radicular symptoms, if the problem is addressed relatively early
  • The outcome is usually unpredictable for relief of back pain
  • If symptoms have persisted for a long time, it is possible that some permanent nerve damage has occurred and decompression cannot restore full functionality
  • Success rates
    • Central stenosis decompression : 65 - 85% good results
    • Nerve root decompression :
      • 62% complete success
      • 24% partial success
    • Degenerative spondylolisthesis : 65% good result

Surgery vs. non-operative treatment

  • Surgery is more effective for treating symptoms of lumbar spinal stenosis in the short term
  • The benefits of surgery relative to non-operative treatment decrease with time, becoming non-significant after 2 -5 years
  • Atlas et al. published a longitudinal cohort study in Spine 2000, the results of follow up of surgically and non-surgically treated patients over 4 years
    • The surgical group had worse clinical and radiological features initially, but had better outcomes than non surgical group
    • This was most apparent at 1 year and still apparent, although less strongly, at 4 years
    • The outcome of non-surgical group improved modestly and remained stable over 4 years 
  • Randomized controlled clinical trials comparing surgery for lumbar spinal stenosis to non-surgical treatments have repeatedly shown that
    • Surgery significantly decreases pain and disability
    • Surgery improves patient satisfaction within the first 2 years following the procedure
    • The most consistent outcome across multiple studies was decrease in pain
    • The most variable outcome across multiple studies was disability
  • Interestingly, randomized trials comparing surgical vs. non-operative treatment were complicated by non-adherence to the randomized treatment groups
    • Significant crossing-over exists between the assigned surgical and non-surgical groups
    • This suggests that patient preference plays a significant role in the decision to operate vs. choose non-operative means
  • Given that surgery provides a short-term decrease in pain, but an uncertain benefit after 5 years, the decision to operate vs. non-surgical management should be made with significant consideration of the individual patient and patient's preferences

Decompression vs. Fusion

  • Arthrodesis may result in significantly less back pain than laminectomy alone after 3 years
  • The relative long-term efficacy of fusion surgery vs. simple decompression needs to be further assessed, as complex fusion surgeries have increased
    • Morbidity
    • Mortality
    • Length of hospital stay
    • Total healthcare costs
    • Unclear comparative long-term benefit
  • If there is no instability, arthrodesis will not improve outcome

Complications

  • The risk associated with treatments for spinal stenosis increases with the degree of invasiveness of the treatment
    • NSAIDs, oral steroids and steroid injections are associated with relatively minimal risk
    • Surgeries for lumbar spinal stenosis are associated with significantly higher complication risks, which correlate with the degree of invasiveness of the surgery
  • In one study, the odds ratio of life-threatening complications with complex fusion surgery was 2.95 relative to the risk of decompression alone, and the odds ratio of re-hospitalisation within 30 days after complex fusion was 1.94 relative to decompression alone
  • Complications include
    • Cardiopulmonary events
      • MI
      • PE
      • Respiratory failure
    • Stroke
    • Wound-related complications
      • Deep tissue infection
      • Healing problems
      • Bleeding
      • Injury to nerves
      • Epidural scarring
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