Overview
This lecture covers exam findings and imaging interpretation for nerve root compressions, focusing on L3-S1, and emphasizes diagnosis and management of disc herniations.
Nerve Root Compression: Key Exam Findings
- L3 compression causes hip abduction weakness.
- L4 compression leads to knee extension weakness and decreased patellar reflex.
- L5 compression results in ankle dorsiflexion and inversion weakness, great toe extension (EHL) weakness, and sometimes hip abduction weakness.
- S1 compression causes ankle plantar flexion weakness and decreased Achilles tendon reflex.
- L5 compression is commonly associated with foot drop.
- S1 compression is typically linked to plantar flexion weakness.
Clinical Correlations & Imaging
- Foot drop suggests L5 nerve root compression, which may be due to far lateral L5-S1 or paracentral L4-5 disc herniations.
- L5-S1 disc herniation often compresses the traversing nerve root.
- Axial MRI images can reveal traversing nerve root compression.
- Far lateral disc herniations may be missed on imaging that only checks the central canal.
- Far lateral disc herniations compress the nerve root near the dorsal root ganglion (DRG), causing severe pain.
- Massive central disc herniations at L4-5 can obliterate the central canal and may cause cauda equina syndrome.
- Large herniations with severe symptoms usually require surgical rather than conservative management.
Key Terms & Definitions
- Foot drop — Inability to dorsiflex the foot, commonly due to L5 nerve root compression.
- Paracentral disc herniation — Disc herniation near the center, often affecting the traversing nerve root.
- Far lateral disc herniation — Disc herniation located outside the central canal, often compressing the exiting nerve root.
- Traversing nerve root — The nerve root that passes by the disc level, often compressed by herniations.
- Foraminal stenosis — Narrowing of the spinal foramen, potentially compressing exiting nerve roots.
- Dorsal root ganglion (DRG) — Nerve cell cluster involved in transmitting sensory information, sensitive to compression.
- Cauda equina syndrome — Severe neurologic condition from massive central canal compression, requiring urgent intervention.
Action Items / Next Steps
- Review nerve root levels and their associated motor deficits and reflex changes.
- Practice interpreting MRI images for central and far lateral disc herniations.
- Understand criteria for conservative versus surgical management in disc herniation cases.