Lower back pain: prolapsed disc
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).
- Incidence: 500.00 cases per 100,000 person-years
- Peak incidence: 40-50 years
- Sex ratio: 1:1
|Lower back pain (non-specific, without sciatica)||6.00|
|Lower back pain: prolapsed disc||1|
|Neoplastic spinal cord compression||0.02|
|Cauda equina syndrome||0.002|
- Increasing age
- Occupation (especially those which requires lifting heavy loads, bending over, and operating machinery)
- 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.
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 root||Main motion affected||Reflex affected|
|L4||Knee extension||Knee jerk|
|S1||Feet plantar flexion||Achilles reflex|
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
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
- Advise patients to go on with daily activities whilst restricting strenuous activities and pain triggering activities.
- 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.
- 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 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
- 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.