Lumbar Stenosis

Introduction

Symptoms typically develop between 50 to 60 years of age in association with lumbar spine osteoarthritic changes
No sex predominance, although degenerative spondylolisthesis associated with lumbar spinal stenosis 4x more common among women
No association found with occupation or body habitus
Usually caused by a reduction in space available for neural elements due to variant osseous anatomy or filling of spinal canal with hypertrophic tissue

Lumbar Stenosis 2

Central stenosis:
- Compression of dural sac is main component
- <10mm canal AP diameter or 100mm² canal cross-sectional area on CT
Lateral stenosis:
- Compression of nerve root in lateral recess, neural foramen, or lateral to neural foramen

Pathophysiology

Usually begins with disk dehydration, resulting in a loss of disk height & bulging of annulus fibrosus & ligamentum flavum into spinal canal
These changes alter loading of facet joints, which together with intervertebral disc form 3-joint spinal motion segment
Further degeneration leads to facet arthrosis with sclerosis & osteophytic overgrowth
Most common result is as nerve roots traverse lateral recesses, they are encroached on by hypertrophic facet joints, infolded ligamentum flavum, & a bulging annulus
These degenerative changes can also cause root stenosis in neural foramen
AP diameter of foramen is reduced by bulging anulus anteriorly & hypertrophic facets posteriorly, while foraminal height is reduced by loss of intervertebral disc height & associated facet subluxation
Degenerative process is sometimes accompanied by development of segmental instability
Degenerative changes in supporting structures of spinal motion segment, including compromise of facet joints & capsular ligaments, may cause higher mechanical stress across degenerated annulus, leading to development of dynamic subluxation or spondylolisthesis
As abnormal motion develops within a degenerated motion segment, it exacerbates nerve root irritation in stenotic lateral recess & foramen

Clinical Manifestations

History:
- Insidious onset & a slow rate of lumbar back pain with progression to lower-extremity pain
- Neurogenic claudication
  - Exacerbated by standing, walking, & exercising in an erect posture, which results in development of pain, tightness, heaviness, & subjective weakness in legs
  - Relieved by sitting down or leaning forward
  - Activities in which lumbar spine is in flexion, such as walking uphill, leaning forward on a walker or shopping cart, or riding a bicycle, are usually better tolerated
- Motor, gait, bowel & bladder dysfunction uncommon
Examination:
- Lumbar lordosis reduced with ROM diminished
- Deep tendon reflexes diminished with complete loss in elderly common

Differential Diagnosis

· Vascular claudication:
- Reproduced at a consistent level of exertion (e.g. walking 2 blocks)
· Diabetic neuropathy:
- Characterised by a stocking-glove distribution

Lumbar Stenosis 3

Imaging

Erect plain radiographs:
- Dynamic views to identify associated instability
MRI:
- 21% asymptomatic individuals aged 60 to 80 years have evidence of lumbar stenosis
- CT +/- myelogram alternative if MRI not available

Management

Non-operative:
- Indication
  - Mild-to-moderate symptoms of neurogenic claudication
- Activity modification & relative rest
  - Activity as soon as tolerated
  - Avoidance of aggravating activities such as heavy lifting & excessive trunk extension, that decrease AP diameter of spinal canal
- Weight loss
- Patient education
- Physiotherapy
  - Flexion-based exercises
  - Stretching of hip flexors, hamstrings & paraspinal muscles, & strengthening of abdominal & trunk muscles
  - Postural correction
  - Hydrotherapy
  - Elastic lumbar binder may provide benefit by reducing loads across lumbar spine, but it should be worn only for a short period of time in order to avoid deconditioning of paraspinal muscles
- Paracetamol & NSAIDs
- Muscle relaxants
- Tricyclic antidepressants
- Narcotic medications
  - Sparingly & for only brief periods for patients with incapacitating pain who cannot tolerate NSAIDs
- Epidural steroid injections
  - Decrease spinal stiffness & can facilitate eventual progression to active phase of therapy
  - Although interlaminar & caudal routes of epidural injection are technically easier than injection through arthritic posterior elements in elderly patients with spinal stenosis, acute radicular pain in a specific nerve-root distribution is best treated with a transforaminal selective nerve-root injection (corticosteroid & bupivacaine) performed under fluoroscopic guidance
  - A selective nerve root block is a good prognosticator of surgical outcome, as patients who obtain >50% relief of leg pain for at least 1 week tend to have ≥50% relief of leg pain, compared with preoperative intensity, within 1 month after surgery & lasting at least 6 months postoperatively
- Prognosis
  - 70% substantial decrease in symptoms & avoidance of surgery

Operative:
- Indications
  - Patients who are functionally limited in terms of both walking tolerance & ADLs
  - Intractable pain, especially neurogenic claudication (leg or buttock pain), that has not responded to non-operative treatment
  - Urgent surgical decompression with a rapidly progressive neurologic deficit &/or cauda equina syndrome (bladder & bowel dysfunction); however this is rare
  - Perfect surgical candidate
    - Severe leg symptoms of a neurogenic claudicatory nature & corresponding stenosis on imaging studies
    - No or minimal axial back pain
    - No or minimal neurologic deficit
    - No evidence of vascular claudication
    - No medical comorbidities
- Principles
  - Even when symptoms are unilateral, bilateral decompression should be performed if there is radiographic evidence of bilateral stenosis because contralateral symptoms will soon develop
  - Another important goal of surgical treatment of stenosis is maintenance of stability of spinal column, which can be facilitated during the decompression by clear identification & preservation of pars interarticularis & by undercutting & preserving at least lateral 50% of facet joints
  - Fusion +/- instrumentation recommended to maintain stability with complex stenosis associated with degenerative spondylolisthesis or degenerative scoliosis (a curve of >30°) or if >50% of facet joints are removed bilaterally during decompression

Technique (laminectomy)
- Loupe magnification
- Prone kneeling position on an Andrews frame to minimise intra-operative bleeding from epidural venous plexus; if internal fixation is planned, a more lordotic position on a Jackson table may be preferred, but more blood loss can be expected
- Midline incision
- Dissection to lumbodorsal fascia
- Subperiosteal dissection exposing spinous processes & lamina
- Lateral radiograph to identify correct level (attach towel clip)
- Dissection is then carried out laterally superficial to facet joints, with care taken to preserve facet joint capsules & to identify pars interarticularis
- Parafacetal arteries that lie medial & lateral to facet joints may cause additional hemorrhage during lateral dissection, but bleeding can be easily controlled with electrocautery
- If a posterolateral fusion is planned, lateral dissection needs to extend to the tips of the transverse processes bilaterally, while intertransverse membrane is maintained
- Inferior half of spinous process at top of decompression & superior half of spinous process of inferior level to be decompressed are removed
- Intervening spinous processes excised
- Any remaining soft tissue removed & lamina thinned
- Bone wax applied to bleeding bone allows maintenance of a dry surgical field
- Ligamentum flavum is identified, & a dissector or curette is used to gently dissect insertion of ligament from undersurface of inferior edge of most caudal lamina, where a central decompression begins
- Removal of laminae should always start centrally, since midline is last area to become stenotic & thus safest place to begin dissection
- Dura protected as decompression extended laterally to pedicles
- Medial facetectomy & removal of any osteophytic ridge adjacent to intervertebral disc space
- Midzone, located anterior to pars interarticularis & inferior to pedicle, can be decompressed with undercutting of hypertrophic facet joints & area under pars interarticularis with a small Kerrison rongeur
- Nerve roots are identified, & neural foramen is probed to make sure it is adequately patent
  - Probe should be passed in an inferolateral direction parallel to course of nerve root
- Discectomy
  - Performed only if necessary to further decompress both exiting & traversing nerve roots & only for extruded soft disc material or a free fragment, since violation of degenerated, well-contained discs may lead to unnecessary destabilisation of anterior column
- Bilateral laminotomies alternative
  - Potential for postoperative iatrogenic spondylolisthesis is reduced by performance of laminotomies, which preserve midline stabilising structures
- Indications for fusion
  - Instability at involved motion segment
  - Degenerative scoliosis (especially with curve progression or a curve magnitude of >30°)
  - Revision decompression at same level, resection of >50% of facets bilaterally
  - ® Degenerative spondylolisthesis
- Prognosis
  - Relief of back pain in 80%
  - Relief of leg symptoms in 95%
  - Good or excellent outcome in 85% after 4 years
  - Best results obtained when surgical intervention carried out within 1^st few years after onset of disease
    - Prolonged structural compromise of spinal nerve roots may lead to chronic & irreversible damage that surgical decompression cannot correct
    - ® Results of surgical decompression are usually better if procedure is performed within a year after onset of symptoms
- Post-operative care
  - Mobilise day 1 post-operatively
  - Avoid bending, lifting or twisting for 6 to 12 weeks
  - Radiographs to monitor for instability or hardware failure
- Complications
  - Epidural hematoma
  - Thromboembolic event
  - Dural tear (especially in revisions)
  - Infection
  - Instability following wide decompression
  - Nerve root injury
  - Nonunion or hardware failure following fusion
  - Adjacent segment degeneration
  - Recurrence of symptoms

Summary

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