Overview
This lecture discusses the types, locations, and anatomical effects of lumbar disc herniations, including their impact on specific nerve roots.
Types and Locations of Disc Herniations
- Central disc herniations are rare and emerge from the center of the posterior disc.
- Paracentral disc herniations are most common, occurring just off center due to weaker posterior ligament support laterally.
- Lateral (foraminal) disc herniations occur in the foramen and can be addressed surgically via a laminotomy.
- Far lateral disc herniations occur outside the spinal canal/foramen and compress the exiting nerve root.
- Far lateral herniations account for about 10–15% of cases.
Anatomical Relationships and Nerve Root Compression
- The spinal nerve roots are likened to cars exiting a freeway: traversing roots move centrally then laterally as they exit.
- The exiting nerve root is above the disc space; the traversing nerve root is below.
- Paracentral herniations typically compress the traversing nerve root (e.g., L3-4 disc herniation compresses L4 nerve root).
- Far lateral herniations typically compress the exiting nerve root (e.g., L3 nerve root at L3-4 level).
Disc Herniation Nomenclature
- Degenerative disc bulge: mild disc protrusion, minimal nerve involvement.
- Prolapse: increased bulging, possible nerve compression.
- Extrusion: disc material breaks through annulus, but remains attached.
- Sequestration: nucleus pulposus fully escapes and separates from the disc.
Key Terms & Definitions
- Central disc herniation — Disc herniation directly from the center of the posterior disc.
- Paracentral disc herniation — Herniation near the center but offset, most common type.
- Lateral/foraminal disc herniation — Herniation into the neural foramen, affecting exiting nerve.
- Far lateral disc herniation — Herniation outside the foramen, compressing the exiting nerve root.
- Traversing nerve root — Nerve passing downward past the disc before exiting.
- Exiting nerve root — Nerve leaving the spinal canal at the disc level.
- Prolapse, extrusion, sequestration — Increasingly severe types of disc material displacement.
Action Items / Next Steps
- Review lumbar spine anatomy, focusing on nerve root paths.
- Study the clinical presentations of different disc herniation types.