Lumbar/Sacral · Lower-extremity pattern aid

Lumbar disc level → nerve root deficit.

Select a disc level and herniation morphology. The tool returns the most likely affected root with its dermatome, myotome, reflex, and bedside clue.

Approximately 95% of lumbar disc herniations occur at L4–L5 or L5–S1 [StatPearls].

Select disc level

Herniation morphology

Why morphology matters

At a given lumbar level, the exiting root leaves through the neural foramen at that level, while the traversing root descends past the disc toward the foramen below. Paracentral herniations sit medial in the canal and compress the traversing root; far-lateral herniations sit out in the foramen and compress the exiting root [StatPearls].

Example A lateral L4–L5 lesion typically causes L5 radiculopathy; a far-lateral L4–L5 lesion typically causes L4 radiculopathy.

Selected level

L4–L5

Affected root L5 paracentral · traversing

Dermatome (sensory)

Myotome (motor)

Reflex

Bedside clue

Dermatomal map

Lumbosacral sensory zones

L5 highlighted

Morphology atlas · Axial schematic

Disc shape changes which root is at risk.

Tap a morphology to morph the axial view and see where the fragment sits relative to the canal, lateral recess, and neural foramen. These are teaching schematics, not diagnostic MRI criteria.

Normal axial relationship

Baseline before herniation: the posterior disc margin stays behind the thecal sac, with clear lateral recess and foraminal corridors.

Reference anatomy — the only labeled diagram.

Traversing-versus-exiting root rules follow StatPearls — Lumbar Disc Herniation.

Comparison matrix

All five disc levels, both morphologies. Tap a row to load it in the tool above.

Disc level	Paracentral → traversing root	Far-lateral → exiting root	Dermatome (autonomous zone)	Motor	Reflex

Autonomous zones from StatPearls — Radicular Back Pain. Motor and reflex columns synthesize StatPearls — Lumbar Disc Herniation and the Merck Manual.