Lumbar disc herniation

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Introduction

  • Malfunction of a nerve root in the lumbar region of the spine, due to compression by an extruding disk or related irritation
  • Sciatica is a common term that refers to pain along the sciatic nerve in radiculopathy

Anatomy

  • There are two foramina underneath each lumbar vertebrae
  • The spinal nerve roots pass through these foramina
  • The foramina are bordered anteriorly by the intervertebral disc
  • The disc consists of an outer annulus fibrosus and an inner nucleus pulposus
  • Nucleus pulposus has the consistency of tooth paste and provides the disc with its shock absorbing qualities
  • The intervertebral disc has blood supply up to the age of 8 years
  • Nutrition after this time is by imbibition and requires movement of the spinal column

Pathogenesis

  • Traumatic
    • Herniation may occur secondary to heavy lifting while bent at the waist
    • Earliest changes are biochemical and trauma may be superimposed
  • Age-related changes in the disk
    • Macroscopically
      • Cracks develop in the disc
      • Disc shrinks and buckles out
      • Disc space narrowing
    • Microscopically
      • The first morphological change probably is damage to the cartilage end plate
      • There are changes in proteoglycan composition of nucleus pulposus
      • The annulus fibrosus becomes fibrotic and develops fissures
      • Circumferential tears develop in the annulus which progress to radial tears
  • Kirkaldy-Willis suggests three stages of degeneration
    1. Dysfunction
      • 15 - 45 years
      • Characterised by circumferential and radial tears in the annulus
      • Localised facet joint synovitis
    2. Instability
      • 35 - 70 years
      • Internal disc disruption
      • Disc resorption
      • Degeneration of facet joints with capsular laxity
      • Joint erosion
      • Subluxation
    3. Stabilisation
      • > 60 years
      • Development of hypertrophic bone around the disc and facet joints
      • Segmental stiffening / ankylosis
  • Disc herniation is a complication of stage 1 and 2
  • Conditions associated with an increased incidence of back problems
    • Scheuermann's disease
    • Transitional lumbar / sacral vertebrae
    • Spondylolisthesis
    • Family history
    • Cigarettes smoking : 18% greater mean disc degeneration scores in the lumbar spines of smokers compared to non smokers in discordant twin study
    • Patients who worked longer hours with a larger "time urgency"
    • Obesity : increased lumbar load is a key risk factors for disk herniation
  • Protective factors
    • Physical exercise
    • Weight loss and/or a normal BMI are important to minimize risk
    • Sleeping on a hard bed

Natural History

Epidemiology

  • Back problems account for 2% of GP presentations
  • 80% of population are affected at some stage in their lives
  • Prevalence is equal in men and women
    • Men typically develop symptoms in their 40's
    • Women are typically affected between 50 and 60
  • Lifetime prevalence is around 3-5% in adults
  • Incidence increases with age

Prognosis

  • Symptoms will resolve in most instances of untreated disease in a few days or weeks
  • Rarely, disk herniation progresses to cord compression / cauda equine syndrome
  • Recovery rate
    • 50 - 60% of back pains recover in one week
    • 90% recover in 3 months
    • The remaining 10% who recover slowest, account for 80% of the costs to the community
  • Relapse rate
    • After 1st episode 90% improve and do not relapse
    • 2nd episode 90% improve and 50% relapse
    • 3rd episode 90% improve and 100% relapse
  • Resuming activity
    • 60% will return to work within 1 week
    • 70% return to work within 2 weeks
      • 25% of the remainder will be off work at 6 months
    • 80% return to work within 6 weeks
      • 45% of the remainder will be off work at 6 months
    • 92% return to work within 6 months
      • Only 35% of the remaining will return to work in next 6 months
    • 70 / 100,000 require surgery

Clinical Presentation

  • Usually aged 20 - 40 years
  • First severe attack may be precipitated by a minor episode of backache (the annular tear)
  • Develops severe back pain while lifting or stooping
  • Presents with lower back pain, stiffness, ± radiculopathy
  • Exacerbating factors
    • Forward flexion
      • Sitting, lifting, going up stairs
      • This is key to differentiate from spinal stenosis
    • Anything that increases intraspinal pressure, such as coughing or straining
  • While symptoms present there is usually a list or scoliosis
    • Toward the side of the lesion, if the prolapse is in the axilla of the root
    • Away from the side of the lesion, if it is lateral to the root
  • There is usually loss of the lumbar lordosis, due to para-vertebral muscle spasm
  • Root compression is characterised by dysfunction of the nerve with weakness ± sensory changes
    • There may be weakness of hip flexion, knee extension and hip abduction
    • Knee / ankle reflexes may be reduced
    • Sensation may be affected from the anterior thigh down to the lower leg
  • 95% of disk herniations occur at the L4-L5 and L5-S1 levels
    • L5 radiculopathy is the most common
    • Presents with back pain radiating down the lateral side of the lower leg
  • It should be noted that these findings are neither sensitive nor specific for disc herniation
    • Many herniated disks are not symptomatic
    • Radiculopathy has a broad differential and is not specific for disk herniation
  • The straight leg raise test (SLR)
    • Raising the patients leg (symptomatic side) from the supine position will increase dural tension in the lumbar levels and may reproduce radicular pain
    • It is a sensitive, but nonspecific test
  • Rarely, disk herniation progresses to cord compression / cauda equine syndrome

Criteria for diagnosis of herniated disc

  • Leg pain (including buttock pain) greater than back pain
  • Dermatomal paraesthesia
  • Root tension signs
    • SLR
    • Bowstring
    • Crossover
  • Root dysfunction
    • Weakness
    • Wasting
    • Sensory dysfunction
    • Reflex changes
  • Correlative imaging study

Differential Diagnosis

  • Lumbar entrapment syndromes
    • Sub-articular entrapment
    • Foraminal encroachment
    • Pedicular kinking
    • Extra-foraminal entrapment
    • Spinal stenosis
      • Symptoms are exacerbated by standing in an erect posture
      • Flexion relieves symptoms
      • Commonly caused by degenerative spondylosis
    • Adhesive radiculitis
  • Cauda equine syndrome
    • May present with radiculopathy
    • Would also expect bowel / bladder incontinence
  • Spinal afflictions
    • Metastasis
    • Abscess
    • Hemangioma
    • Hematoma
  • Cervical myelopathy
    • May cause a myelopathic state with lower leg signs and symptoms
    • Urgency of micturition is a classical feature of cord pathology
  • Sacroiliitis may also cause lower back pain with radiculopathy
  • Non-organic pain
    • May play a major role in initiation / maintenance of symptoms in some patients
  • Inappropriate sigs of Waddle are helpful
    • Superficial and non anatomic tenderness
    • Simulated test pain; e.g. during slight axial loading or rotation
    • Alteration in severity or presence of pain if distracted (SLR particularly)
    • Regional sensory/motor disturbances that do not follow anatomical distributions
    • Over-reaction is the most important non-organic physical sign, but also the one most influenced by the subjective impressions of the observer
  • Remember, those with psychosomatic / malingering tendencies may latch onto a positive MRI, though a disc on MRI may simply be incidental and of no significance
  • The presence of non organic signs, even in presence of definite pathology, may identify those patients requiring formal psychosocial assessment before surgery

Psychosocial impact of the disease

  • Lower back pain is commonly associated with depression
  • The pain can be persistent and may generate limitations in a patient's daily activities
  • While a causal relationship has not been established, mental side effects of chronic pain can be substantial

Imaging and Diagnostic Studies

X-Ray

  • Very insensitive for the diagnosis of disc herniation
  • Helpful for narrowing the differential and ruling out tumors, infections and fractures

Discography

  • Determines
    • Morphology of the disc
    • Patient's response to injection
  • 89% of patients in whom discography had demonstrated disc disease and provoked symptoms had significant and sustained benefit from operation
  • Specificity 100%
  • Discography identifies painful levels when contemplating spinal fusion

CT Scan

  • Better soft tissue resolution than X-Ray, but inferior to MRI
  • Shows the shape and contents of the spinal canal, as well as the surrounding soft tissue

Myelography

  • Confirms level of pathology
  • Usually combined with CT scan
  • Water soluble non ionic contrast medium used; e.g. metrizamide or iopamidol
  • 60% accurate in diagnosis of lumbar disc herniation
  • Suspect sequestered fragment, if defect is seen cephalad or caudad to the disc space and extends over more than 3 CT cuts
  • CT advantages over myelography
    • Better visualisation of lateral lesions
    • Lower radiation dose
    • No adverse reactions
    • Differentiates between bony and soft tissue compression
  • Accuracy of different modalities for diagnosis of lumbar disc herniation
    • Myelography : 60%
    • Plain CT : 74%
    • CT with contrast : 77%
    • CT discography : 87%

MRI

  • Sensitive modality that identifies most pathologies
  • A protruded disc on MRI may simply be incidental and of no significance
  • Normal MRI does not rule out disc degeneration
  • T2 MRI may show the extension of a disk protruding from the disk space
  • A black disk indicates lack of water, which is consistent with degenerative disk disease
  • Classification
    • Contained protrusion
    • Non-contained herniations
      1. Sub-ligamentous or sub-annular extrusion
      2. Trans-ligamentous extrusion
      3. Sequestered fragment
      4. Intradural (rare)

Gadolinium-DTPA

  • Useful in evaluation of the postoperative spinal adhesions
  • 96% sensitivity for distinguishing epidural fibrosis from recurrent disc herniation
  • Epidural scar has a blood supply and enhances after injection of Gd-DTPA, whereas disk herniation does not enhance

Laboratory evidence

  • There are no true laboratory abnormalities helpful for diagnosis of disk herniation
  • Normal lab values may rule out other possible etiologies of low back pain
  • EMG may be used to distinguish weakness secondary to pain-related reduced effort from neurogenic weakness, which may be observed in nerve root compression

Other investigations

  • Facet joint injection : no benefit in treatment of chronic LBP
  • Differential epidural nerve root block
    • Patient grades pain 1-10 during procedure, using varying concentrations of long acting local anesthetics
    • Those not helped by a full spinal are unlikely to be helped by surgery
  • Psychological testing
    • MMPI : scores > 75 for hysteria and hypochondriasis indicate poor prognosis
    • Zung Depression Scale combined with Modified Somatic Perception Questionnaire is the best discriminator in a comparison of 8 psychometric tests

Treatment

Always think root, not disc

Conservative management

  • Physical therapy
    • Good for pain relief but no proven benefit
    • Traction reduces intra-discal pressure, but pain often recurs on removal of traction
  • Lumbar back support
  • NSAIDs
  • Epidural injection of local anaesthetic / steroid
    • 60 - 85% success in short term
    • 30 - 40% success in the long term
  • Weight loss
  • Exercise to strengthen abdominal and extensor muscles, once acute attack is over
  • Back education results in 70% subjective improvement in symptoms
  • In the management of acute back pain there is no real place for the use of
    • Muscle relaxants
    • Oral corticosteroids
    • Antidepressants
  • Spinal manipulation/chiropractic treatment is contraindicated

Surgical management

  •  Indications of surgical intervention for acute LBP
    • Pain refractory to conservative management
    • Bowell / bladder incontinence
    • Neurological deficits
  •  Indications of surgical intervention for chronic LBP
    • Chronic and disabling LBP ± leg pain, severe enough to prevent work/activity
    • Failure of conservative treatment for 6 months
    • Well localised pathology on investigation (MRI, discography)
    • Realistic patient expectations
  • Contraindications
    • No definite pathology to explain symptoms
    • Multiple level degeneration, where symptoms cannot be localised
    • Major psychological stress
  • Options
    • Fusion of involved segments : usually for chronic cases
    • Laminectomy
      • The lamina of the vertebra is removed to increase the size of the spinal canal to decompress spinal nerves
      • Also a common treatment for spinal stenosis
    • Discectomy : the nucleus pulposus is removed to decompress the affected nerves
    • Chemo-nucleolysis : The disk is chemically dissolved
      • Proteolytic enzyme from papaya latex
      • Does not affect annular collagen, but disrupts proteoglycan structure
      • Induces hydrolysis of cementing protein of the high molecular weight; glycosaminoglycan
      • Decreases the water binding capacity with a reduced disc pressure and volume
      • Indications
        • Should have failed adequate trial of conservative treatment
        • Fulfil the diagnostic criteria for disc herniation
      • Contraindications
        • Absolute
          • Allergy
            • Hypersensitivity reported in 1.5%
            • Anaphylaxis reported in 0.5%
          • Rapidly progressive neurological deficit
          • Possibility of spinal cord tumour
          • Massive herniation
            • Protrusion is greater than 3 CT cuts
            • Fragment occupies > 50% canal diameter
        • Relative
          • Severe spinal stenosis
          • Pregnancy
          • Previous treatment with Chymopapain (? sensitivity)
          • Severe arachnoiditis
      • Technique
        • Test dose of 0.3 ml used
        • If no reaction after 10 minutes, give the remaining 1.2 ml
        • Total therapeutic dose is 3,000 units of the enzyme
        • Should be administered with antibiotics
      • Results : Gogan and Fraser Chymopapain; a 10 year double blind study
        • 80% of chymopapain group regarded injection as successful vs. 34% of saline group
        • 20% of chymopapain group required surgery vs. 47% of saline group
      • Complications
        • May get increased back pain after injection
        • Anti-inflammatory medication, walking and swimming are the best modalities used during convalescence

Outcome

  • Most herniated disks will heal without treatment
  • The results of all forms of treatment need to be compared with the natural history of the disease
  • The most important criterion for success remains the proper selection of patients
  • Conservative
    • 70 - 90% recover with a combination of rest and analgesia
    • It has been shown in one study that 73% of patients displayed reasonable to major improvement without surgery
  • Surgery
  • De-compression (discectomy, laminectomy)
    • 90-95% success in relief of leg pain
    • 80% success in relief of back pain
    • Results are same for conventional discectomy as for micro-discectomy
    • Long term results after discectomy not significantly different than those after no surgical treatment
  • Fusion : 66% satisfactory outcome
  • The Hague Spine Intervention Prognostic Study Group found that rates of pain relief and perceived recovery were faster for patients assigned to early surgery, although 1 year outcomes were similar for conservative treatment plus eventual surgery as needed versus early surgery

Complications

  • Neurological damage
  • Wound infections
  • Discitis
  • CSF fistula
  • Haematoma
  • Great vessel injury
  • Pulmonary embolus
  • Late stenosis
  • Instability
  • Secondary scaring
  • Arachnoiditis

References


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