Lumbar Disc Prolapse

Definition

  • disc bulge
    • generalized outpouching of peripheral margin of annulus
  • disc prolapse
    • focal displacement of inner disc material
  • protrusion
    • disc bulging beyond limits of vertebral body
  • extrusion
    • disc material thru annulus fibrosus & PLL
  • sequestered
    • complete displacement with free disc fragment

Aetiology

Epidemiology

Incidence

  • 56% of adults have disc bulging
  • MRI scans show that between 20% & 35% of working age adults have asymptomatic disc herniation
  • There is lifetime incidence of 2% for symptomatic disc herniation
  • 80% of general population will experience back pain but only 2-3% will have sciatica
  • mean onset = 35 years
  • unusual < 20 years & > 60 years
  • males = females (females present decade later than males)

Age

  • Most lumbar disc herniations occur between 30 & 50
  • Far lateral disc herniations occur in older age group (average age 65)
  • Lumbar disc herniations before 30 tend to have hereditary aetiology

Site

  • commonest site for prolapse is L4/L5 disc, then L5/S1 disc

Risk factors for back pain

  • obesity
  • smoking
  • M:F
  • Job: Lifting, vibration, sitting
  • Job satisfaction ++

Anatomy

  • prolapsed disc impinges on nerve root of second vertebra in motion segment; thus L5/S1 disc prolapse presses on S1 nerve root
  • This is true for posterolateral prolapse, but for far lateral prolapse disc presses on nerve root of vertebra above; thus in far lateral L5/S1 disc prolapse L5 nerve root can be affected

Pathology

  • Decreased water content & proteoglycan content
  • Increased peripheral annular loading
  • annular tear
  • Decreased of disc space
  • Increased stress at facet joints
  • degeneration of facets with osteophyte formation
  • traction spurs
  • recurrent torsional strains
  • lumbar spondylosis
    • disc dessication
    • collapse
    • progressive facet arthrosis
    • disc bulging
    • osteophytosis
    • abnormal kinematics
    • further degeneration
  • LDH occurs as result of annular degeneration leading to weakening of annulus fibrosis, leaving it susceptible to annular fissuring & tearing
  • Two types of disc disease:
    • 1. Compressive
      • will have hard neurological signs
    • 2. Chemical
      • will not have hard neurological signs
  • Chance of resorption of disc fragment depends on its size & its nature
    • Smaller disc fragments are less likely to be resorbed
    • sequestrated disc fragments are more likely to be resorbed than contained fragments
    • Best prognosis for resolution is large sequestrated fragment

Biochemical features of disc disease

  • degenerated discs have higher concentrations of inflammatory mediators, such as IL-1, nitric oxide, PGE-2 & MMPs. Phospholipase A2 is found in higher concentrations in degenerate disc material
  • discs also manifest stronger response to IL stimulus
  • Degenerate discs have denser innervation than normal discs

Classification

Three pathoanatomical types of disc disease

  • 1. Contained LDH
    • disc fragment is bounded by annulus
  • 2. Extruded LDH
    • disc fragment escapes through defect in annulus but is in continuity with rest of disc
  • 3. Sequestrated LDH
    • free fragment

Anatomical position of herniation can be classified as:

  • Central
    • this can affect traversing nerve roots bilaterally, & cauda equina if large enough
  • Posterolateral
    • this is commonest site. herniation is to one side of PLL
    • impingement of nerve root of lower vertebra
  • Foraminal
    • impingement of exiting nerve root (vertebra above)
      • 10%
  • Extraforaminal or far lateral

History

  • fit adult of 20-45
    • When stooping to pick something up patient suddenly experiences severe pain & is unable to straighten up
  • Pain
    • caused by irritation of annulus & posterior longitudinal ligament, which are both well innervated
    • Pain in buttock & lower limb may be immediate or felt day or two later
    • Increased with
      • Coughing & straining
      • sitting
      • forward flexion
  • sciatica/radiculopathy
    • leg pain in dermatomal distribution
  • constitutional symptoms

red flags

  • young/old patient
  • night pain
  • rest pain
  • bowel/bladder symptoms
  • hx of Ca
  • tumour, infection, trauma, cauda equina syndrome

Cauda equina syndrome

  • rare
  • ↑ risk
    • stenotic canal
  • features
    • bilateral leg weakness
    • saddle anaesthesia
    • urinary retention

Examination

Look

  • sciatic scoliosis
  • knee on affected side may be bent to ↓ tension in affected nerve root
  • lean towards affected side
    • posterolateral disc herniation, where disc lies medial to nerve root, lean is towards painful side, to relieve tension
  • lean away from affected side
    • far lateral disc herniation lean is away from painful side

Feel

Move

  • Decreased ROM
    • All back movements, & particularly flexion & side bending away from prolapse are restricted

Special Tests

  • Tension signs
    • Most important, most predictive physical finding
  • SLR (L5 S1)
    • Straight leg raising is limited on affected side
  • Cross straight leg raise
    • major central disc prolapse
    • more sensitive than ipsilateral straight leg raising test
  • Sciatic stretch test
    • refers to lowering leg slightly & dorsiflexing foot & was first described in 1901 by Fajersztajn, who also described crossed straight leg raising test
  • bowstringing test
    • may be positive, but is much less precise
  • Lasègue’s test
    • In 1881 his pupil Forst described lifting foot of supine patient with one hand & keeping knee extended with other
    • He wrote, “It is only necessary to lift limb few inches for patient to experience acute pain at level of sciatic notch just at emergence of nerve” i.e. in buttock. This is not true sciatica, which should extend below knee
  • Femoral stretch test (L3 L4)

Neurological examination

  • Weakness affected nerve root
  • ↓ reflexes
  • paraesthesia in dermatomal distribution

Waddell’s nonorganic tests

  1. superficial tenderness
  2. simulation tests (axial loading & rotation)
  3. flip test
    • extending leg in sitting position is negative but SLR in supine position is markedly positive
  4. nonanatomic weakness & sensory findings
  5. overreaction

Investigations

Indications

  • Pursue red flags
  • Failed non-op Treatment
  • Not in 1st month

X-ray

  • Vacuum phenomenen
  • Traction osteophytes
  • Discogenic osteosclerosis
  • ↓ disc height
  • spondylolithesis

MRI

  • changes of degenerative disc disease
  • sensitive & specific but clinical correlation essential
  • End plate changes:
    • parallel bands of high or low signal adjacent to vertebral body end-plates
  • Abnormal MRI – asymptomatic
    • Age 20-40
      • 20% HNP
      • 30% bulge degeneration
    • Age 40-60
      • 20% HNP
      • 60% bulge / degeneration
    • Age 60-70
      • 40% HNP
      • 20% stenosis
      • 90%% bulge / degeneration

CT scan

EMG / NCV

  • Limited use

Modic Classification

Modic type I

  • Decreased signal intensity T1
  • Increased signal intensity T2
  • Found in 4% of cases
  • Must be distinguished from disc space infection
  • In disc space infection discs have ­signal intensity on T2 weighted images, & in degeneration discs have ¯ T2 signal intensity

Modic type 2

  • Increased signal intensity T1
  • Isointense or slightly ↑ intensity on T2
  • Found in 16% of cases
  • Represents fatty marrow conversion

Modic type 3

  • Low signal intensity on both T1 & T2 weighted images representing bony sclerosis seen on plain films

Differential Diagnosis

  • Disc rupture affects at most two neurological levels; if multiple levels are involved neurological disorder should be suspected
  • In disc rupture, pain is generally intermittent, except for large central disc herniation. With severe, unrelenting pain one should suspect tumour or infection
  • Very young & very old people seldom sustain acute ruptures
    • In adolescents
      • infection
      • benign tumour
      • spondylolisthesis
    • elderly
      • compression fracture
      • malignant disease
  • Consider herpes zoster; pain precedes skin eruption
  • Other differential diagnosis
    • Lyme disease
    • Diabetic amyotrophy
    • Multiple sclerosis
    • Idiopathic lumbar plexopathy
    • All of these four conditions can present with painful radiculopathy & subtle sensory changes

Treatment

Nonoperative management

  • 6 weeks
    • Education
    • Lifestyle
      • Weight loss
      • Quit smoking
    • Physical therapy
      • Bed rest should be for no more than 2-3 days
      • exercise (swimming, biking, walking), abdominal/low back stretching & strengthening
    • Orthotic
      • nil
    • Medications
    • Injections
      • prospective trial has demonstrated benefits of series of up to 4 epidural nerve root injections, with reduction in need for surgery
  • Results
    • Nonoperative management will fail & require surgery in around 15%

Operative Management

Types

  • Discectomy
    • Open vs scope
  • Laminotomy

Indications for discectomy

Absolute

  • Cauda equina syndrome.
    • within 48 hours of onset
  • Rapidly progressive motor deficit

Relative

  • Persistent sciatica &/or neurologic deficits despite 6 weeks of conservative therapy
  • Recurrent sciatica &/or neurologic deficits
  • Significant motor deficit with positive sciatic tension signs
  • Disc herniation into stenotic canal
  • Unremitting pain – disabling

Surgical candidate

  • 1. Sciatica
  • 2. Abnormal neuro finding
    • often subtle
  • 3. Tension sign
  • 4. Confirmatory MRI
  • 5. failed nonoperative Tx

When considering surgical treatment for patient with relative indications for surgery four factors need to be considered:

  • Duration of radicular symptoms
  • Quality & severity of symptoms
  • Type & size of herniation
  • Contained, extruded, sequestered
    • Small vs. large
  • Presence or absence of spinal stenosis

laminotomy & discectomy

  • 95% good results if above is achieved
    • 95% relief of leg pain
    • 15-30% persistent back pain
    • neuro recovery
      • 50% motor or sensory
      • 25% reflex

Procedures

Posterolateral herniation

  • prone with midline incision
  • unilateral exposure of spinous process, lamina & facet capsule
  • correct level confirmed by xray
  • removal of ligamentum flavum & inferior aspect of lamina
  • can undercut medial aspect of superior facet for patients with concomitant lateral recess stenosis
  • identify nerve root & retract
  • disc removed with pituitary rongeur
  • irrigation & hemostasis

Far Lateral Disc

  • Far lateral & intraforaminal disc lesions cannot be easily removed through midline approach
  • Although taking down entire facet is one alternative advocated by some, extraforaminal approach has been advocated by Wiltse
  • Paramedian approach
    • popularized by Wiltse (muscle-splitting approach)
    • Make incision 5 cm from midline, followed by blunt dissection of paraspinal muscles
    • At this point, take radiographs to verify level & clear transverse processes of soft tissues
    • Enter intertransverse ligaments & fascia with knife or curet, then remove those structures between transverse processes
    • Identify nerve, which is usually 2 to 4 mm anterior to fascia & directed at 45° angle
    • Follow nerve medially & identify disc

Management of Durotomy

  • Cover defect with patty
  • Place patient in Trendelenburg
  • Expose durotomy & repair with 5.0 or 6.0 nylon under loupe magnification
  • If unable to repair (e.g. root sleeve or ventral surface)
    • Gelfoam & Tisseel
    • Water tight closure in layers
  • Ask anesthetist to perform Valsalva maneuver to ensure water tight repair
  • Closure in layers to avoid meningocele

Complications

Intraoperative

  • Wrong level & wrong side surgery
    • essential to check position intraoperatively with XR
  • Vascular catastrophe
    • avoidable if ALL is not broached. Treatment of pulsatile bleeding is to close wound immediately, turn patient over & do laparotomy to identify site of bleeding. Mortality can be up to 50%. Complications can include false aneurysm & AV fistula
  • Nerve damage
    • Nerve root – higher rate with conjoined nerve roots
    • Hypogastric plexus, leading to retrograde ejaculation
  • Durotomy 1%
    • Watertight closure & repair
    • Patch
    • Subarachnoid drain for 4-5 days
    • Recurrent HNP 3-11%
    • Vascular catastrophe

Early postoperative

  • Haematoma
  • Infection
  • Retained disc fragment

Late postoperative

  • Recurrent disc herniation.
    • There is no rate in reduction of recurrent disc herniation with aggressive debridement of disc space, so only free fragments should be removed. Revision discectomy may be required in up to 15% of patients; recurrent disc herniation doesn’t respond to nonoperative management as well as primary herniation
  • Discitis
    • 3-6 weeks posterior op
    • severe onset of buttock pain
    • MRI with GAD
      • ↑ signal in disc space
  • Instability
  • Arachnoiditis

Prognosis

Natural History

Postacchini, Spine 1996

  • 60% recover in 1 week
  • 90% 1 month
  • 95% recovery in 3 months with low back pain
  • 75% recovery in 3 months with sciatica
  • op vs nonop
    • results equal at 4 years
    • almost equal at 1 year
    • due to prevalence of back pain
    • nonop Treatment best usually
  • There is favorable response to nonoperative treatment, even in presence of neurological deficit
  • Thus, isolated neurological deficit without function impairing pain doesn’t warrant surgical intervention
  • Several studies have shown that most herniated discs reabsorb with time, particularly large & herniated or extruded discs
  • Conservative measures should be trialled for 6 weeks before surgery
  • For patients with persistent pain & neurologic compromise unresponsive to conservative measures surgery should not be delayed beyond 6 months because of risk of chronic disability

Results

  • Optimal treatment for static motor loss without pain (does this exist?) is controversial & there is no evidence that surgical decompression will result in speedier return of function than non-surgical care
  • Surgery
    • 90% relief of leg pain
    • 30% persistent back pain
    • Neuro recovery
      • 50% motor
      • 50% sensory
      • 25% reflex

Results of open discectomy through limited laminotomy

  • 90% of properly selected patients experience successful short-term relief of symptoms
  • There is progressive decline in success resulting from subsequent degenerative changes.

Microdiscectomy vs. open discectomy

  • Microdiscectomy causes less postoperative pain & patients leave hospital & return to work sooner. negatives include steep learning curve, difficulty in controlling postoperative bleeding & higher rate of disc space infections
  • Microdiscectomy is contraindicated in patients with spinal stenosis or those with sequestered fragment

Percutaneous discectomy

  • technique is unsuitable for patients with stenosis, sequestrated discs, lateral nerve root impingement, spondylolisthesis & prior surgery that may have obscured anatomy
  • It is done prone, with local anaesthetic & sedation. It can usually be done as day stay procedure
  • Because spinal canal is not entered it doesn’t cause epidural fibrosis or arachnoiditis. fenestration of annulus outside spinal canal decreases intradiscal pressure
  • This has reported success rate of 88%
  • success rate at L5-S1 is lower, 50%
  • commonest reason for failure is lateral recess stenosis. Any operative failure can be retrieved by open laminectomy