Introduction

It is estimated that 8 out of 10 adults will suffer from lower back pain at some point in their lives. Most cases of lower back pain are not life-threatening and will usually resolve within 6-8 weeks with conservative treatments.

Prolapsed disc, also known as intervertebral disc herniation, is a common cause of lower back pain. This is a complex, degenerative condition affecting the spine. It is characterised by lower back pain with or without neurological symptoms.

The most common vertebral levels affected are L5/S1 followed by L4/L5, this is due to the high torsional strain and weight within the spinal column at these levels. Intervertebral disc prolapsed usually affects patients from 40s to 50s, especially males (ratio of male to female is 3:1).

Epidemiology

  • Incidence: 500.00 cases per 100,000 person-years
  • Peak incidence: 40-50 years
  • Sex ratio: 1:1
Condition Relative
incidence
Lower back pain (non-specific, without sciatica)6.00
Lower back pain: prolapsed disc1
Bone metastases0.20
Neoplastic spinal cord compression0.02
Cauda equina syndrome0.002
<1 1-5 6+ 16+ 30+ 40+ 50+ 60+ 70+ 80+

Aetiology

Risk factors associated with prolapsed disc:
  • Increasing age
  • Smoking
  • Genetic
  • BMI
  • Occupation (especially those which requires lifting heavy loads, bending over, and operating machinery)

Pathophysiology

A prolapsed disc is a progressive degenerative clinical condition.
  • Over-time, the nucleus pulposus losses the mechanical abilities to withstand the pressure and weight of the body.
  • Annular fibrosis surrounding the nucleus pulposus weakens with age and tears due to the recurrent strain
  • A weakening of the posterior longitudinal ligament.

All of the above contributes to the herniation of the nucleus pulposus into the spinal canal.

The prolapsed disc will exert two types of effect on the surrounding structures:
  • Mechanical neural compression:
    • The prolapsed disc can cause compression of nearby nerve roots and/or cauda equina causing neurological symptoms
  • Inflammatory response
    • This is due to increased production of pro-inflammatory products such as IL-1, IL-6, IL-8, IL-10 and TNF-alpha. These chemicals will stimulate nearby structures especially the paraspinal muscles causing them to spasm resulting in the characteristic back pain. Substance P and phospholipase A2 are also released which results in heightened pain sensation.

Clinical features

95% of prolapsed disc cases are incidental findings and hence asymptomatic.

In the remaining symptomatic 5%, symptoms can generally be grouped into five main categories:
  • Lower back pain (most common complaint).
  • Radiculopathy (dependent on the dermatome).
  • Neurological weakness.
  • Paraesthesia in the affected dermatome.
  • Cauda equina symptoms:
    • Bilateral leg pain and/or weakness.
    • Saddle anaesthesia.
    • Bladder/bowel incontinence.

Positive physical signs are usually associated with neurological features:
  • Straight leg test positive from 30 to 70 degree (known to be the most sensitive examination for lumbar disc herniation, especially nerve root L4-S1). This will reproduce a shooting electrical sensation down the affected dermatome.
  • Restricted lumbar spinal movement due to paraspinal spasm.
  • Lower limb neurological examination:

Affected nerve rootMain motion affectedReflex affected
L3Hip adductionNone
L4Knee extensionKnee jerk

L5
Ankle dorsiflexionNone
S1Feet plantar flexionAchilles reflex



Investigations

Disc prolapse is usually a diagnosis of exclusion. Important differentials such as tumour, trauma, fracture, discitis and inflammatory causes (ankylosing spondylitis, psoriatic arthropathy) should be ruled out first.

A definitive diagnosis of lumbar disc herniation can only be done with the aid of medical imaging. Magnetic resonance imaging (MRI) scans considered to be the gold-standard due to its high sensitivity in assessing soft tissue pathologies. In most cases, a sagittal view and a coronal view will be obtained to accurately assess the level of disc herniation and nerve root affected.

If MRI scans cannot be tolerated, CT-myelogram can be used as a substitute which provides a relatively good picture of the spinal cord and nerve roots.

Other investigation to rule out other differential diagnoses:
  • Spinal x-ray
  • Nerve conduction studies
  • Lumbar puncture

Differential diagnosis

Lower back pain can be attributed to a multitude of causes which includes cauda equina, spinal trauma, spinal fracture, tumour (both primary and metastatic spinal cord compression), discitis (infection), spondylolisthesis, and inflammatory conditions (ankylosing spondylitis, psoriatic arthritis, rheumatoid arthritis and systemic lupus erythematous).

Other differentials to consider includes:
  • Mechanical back pain (especially activity and/or occupational-related)
  • Vertebral osteoarthritis
  • Synovial cyst
  • Intra-abdominal pathologies such as abdominal aorta aneurysm, pyelonephritis, and kidney stones

Red flags for back pain:
  • Weight loss
  • Thoracic back pain
  • Age < 20 and > 55
  • History of malignancy
  • Cauda equina symptoms
  • Fever
  • Trauma

Management

Majority of the patients will recover within 6 to 8 weeks with simple conservative management. NICE recommends the use of risk stratification system such as STarT back risk assessment tool to aid management planning.


Conservative

  • Advise patients to go on with daily activities whilst restricting strenuous activities and pain triggering activities.
  • Physiotherapies
  • Analgesics (NICE recommend NSAIDs instead of paracetamol as first-line for pain relief)
  • If radiculopathy is present, NICE recommends the use of the following medications as first-line; amitriptyline, duloxetine, gabapentin or pregabalin.
  • Corticosteroid epidural injection can be offered in a specialist clinic.


Surgical

  • Indications:
    • Cauda equina (emergency referral to a neurosurgeon)
    • Progressive neurological weakness
    • Pain lasting > 6 weeks which does not respond to conservative management
  • Most common technique used to decompress the spine is laminectomy + micro-discectomy. Spinal fusion usually indicated in the presence of spinal instabilities.

Complications


Complications due to disease progression

  • Sciatica/radiculopathy (if not yet)
  • Loss of height and lumbar lordosis
  • Foraminal stenosis


Complications due to the surgery

  • Re-herniation of the disc
  • Post-surgical infection (wound infection, meningitis, discitis)
  • Injuries to adjacent structures
  • Haematoma within the spinal canal resulting in compression of the spinal cord and/or adjacent nerve roots
  • Spondylolisthesis

Prognosis

The prognosis for prolapsed disc is usually very good.
  • At least 90% of the patients will recover over 6-8 weeks with or without conservative management. This is due to the re-absorption of the prolapsed disc over-time.
  • Only 5% of the patients with acute lower back pain will continue to develop chronic lower back pain (defined by lower back pain lasting > 12 weeks)

The severity of the disease does not correlate with the size of the herniated disc on imaging studies.