Spinal Stenosis

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 5^th 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 3^rd, 4^th and 5^th 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