Lumbar disc herniation

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