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PH-MS05

Disc prolapse and radiculopathy

How an ageing intervertebral disc tears and lets its nucleus escape, how that compresses and inflames a nerve root, and how the pattern of pain, numbness and weakness reveals which root is affected and when it is an emergency.

By the end, you can

  • Describe the structure of an intervertebral disc and the relation of nerve roots to it.
  • Explain how degeneration and loading lead to annular tears and herniation of the nucleus.
  • Explain why a posterolateral L4–L5 herniation usually affects the L5 root.
  • Relate radicular pain, dermatomal numbness, weakness and reflex changes to root compression.
  • Explain the mechanism and warning signs of cauda equina syndrome.
  • Recognise the classic appearances, grades, key numbers and tests of disc herniation, tell radiculopathy from myelopathy and its mimics, and explain how the main treatments act on the mechanism.

What it is

A disc prolapse (herniation) is displacement of the soft centre of an intervertebral disc, the nucleus pulposus, through a tear in its tough outer ring, the annulus fibrosus. Radiculopathy is dysfunction of a spinal nerve root, here caused by the herniated material compressing and inflaming it, with pain, sensory change or weakness in that root’s territory.

2 types to tell apart
Bulge, protrusion, extrusion, sequestration
Increasing degrees of displacement, from a broad bulge of the annulus to a free fragment separated from the disc.
Lumbar and cervical
Most occur at L4–L5 and L5–S1, causing sciatica; cervical herniations, mostly at C5–C6 and C6–C7, cause arm pain.

US spelling: centre → center, fibres → fibers.

Normal function

The intervertebral disc and its nerve roots

Each joins two vertebral bodies. Its centre, the , is a water-rich gel of proteoglycans that spreads compressive load. It is held by the annulus fibrosus, layers of collagen fibres angled in alternating directions like a radial tyre.

Behind the disc lies the vertebral canal. Below the end of the spinal cord (around L1–L2), it contains the , a bundle of nerve roots descending to their exit levels. The runs down the back of the vertebral bodies and discs but narrows in the lumbar spine, leaving the back corners of the disc less supported.

In the lumbar spine each root leaves through the intervertebral foramen below the vertebra of the same number, so the L4–L5 disc lies just above the L4 root’s exit, in the path of the descending L5 root.

Point to it on the model