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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 1

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 1st 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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