The hand reads 6-7-8. The foot reads 4-5-1. These are the exact levels boards love to bury in a vignette. Learn the map, then split a nerve root from a peripheral nerve in seconds.
Start where most people slip. A sensory level is not a guess, it is a landmark. Read the patient, then call the cord level.
Why this trips people: the belly button feels mid-torso, so the instinct is to call it a mid-thoracic level like T6 or T7. The umbilicus has its own fixed address, and it is lower than it feels.
A 24-year-old man is brought to the emergency department after a diving injury into shallow water. He cannot feel pinprick or light touch below a sharp horizontal line at the level of his umbilicus. Sensation is intact above that line. He has bilateral leg weakness and absent ankle reflexes.
The cord injury sits at which sensory level?
Umbilicus is T10. A sensory level at the belly button puts the cord lesion at T10.
The xiphoid is T6 and T7, which is why those felt close. But the umbilicus sits lower than it looks. The fixed anchors going down the front: T4 at the nipple, T6 and T7 at the xiphoid, T10 at the umbilicus, L1 at the groin. The absent ankle reflexes (S1) and leg weakness just confirm the cord is involved below the lesion.
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The Landmark Map
Tap a labeled band on the body. The level and its hook appear on the right. These are the keep-these anchors that show up again and again.
Tap a colored band on the body to reveal its nerve root level and the memory hook that locks it.
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The Hand reads 6-7-8
Tap each digit. Lateral to medial, the hand counts up: thumb is C6, middle finger is C7, little finger is C8. The shoulder badge over the deltoid is a different level entirely.
Tap the thumb, middle finger, or little finger to lock its root level.
Contrast trap: the patch over the deltoid, the regimental badge area, is C5 and the axillary sensory branch. That is a shoulder level, never a hand level. If a stem numbs the shoulder cap, do not reach for a finger answer.
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The Foot reads 4-5-1
Tap a region of the foot. Medial to lateral, the foot counts L4, then L5, then S1: inner ankle is L4, the dorsum and big toe are L5, the outer edge and heel are S1.
Tap the inner ankle, the dorsum or big toe, or the outer edge to reveal its root level.
High-yield detail: the first web space, the skin between the big toe and second toe, is pure L5. It is the cleanest spot to test L5 on a real foot. Numb there with weak big-toe lift equals an L5 problem.
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Map the Rash
A patient walks in with a band of blisters. Watch where it erupts, then call the level. A real dermatome stops dead at the midline. That is the whole tell.
The Patient
Dolores
Age 71 · Day 3 of a burning rash
"It started as a tingling stripe across my left side. Now there are little blisters, all in one band. It burns like a sunburn that only landed in one place."
Find the level
The blisters sit in a band across the lower ribs, just below the nipple line, on the left. Tap the band where they erupt.
Pattern Locked
Single Band, Hard Stop
RouteDorsal root ganglion reactivation in one nerve root
PatternGrouped vesicles in a single dermatome that stop at the midline
PearlNothing in a true dermatome crosses the midline. A band that respects the midline is a root, never a peripheral nerve.
Dolores had a thoracic reactivation. The level was T7, along the lower ribs.
Two shapes, side by side
A root gives a stripe that follows the body map. A named nerve gives a patch that ignores it. Switch between the two profiles.
Nerve roota stripe down the map
Peripheral nervea patch that crosses lines
Nerve root
A stripe that follows the dermatome chart
Follows the body-map stripe and climbs the limb past the wrist or ankle
Often pairs with a reflex change at that level
Pinky plus a medial-forearm stripe equals C8, not a wrist nerve
A shingles band stops dead at the midline
A stripe that climbs the limb and follows the map is a root.
Peripheral nerve
A sharp patch that ignores the chart
Sharp named-nerve patch that crosses root stripes
Stops at a named border like the wrist crease
Spares the forearm or the leg above the lesion
Carpal tunnel numbs three fingertips; ulnar is the pinky, stopping at the wrist
A patch that crosses lines and spares the forearm is a named nerve.
Root or nerve? Make the call.
A named nerve gives a sharp patch that crosses dermatome lines. A root gives a stripe that follows the body map. Decide each one, then check yourself.
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Reflexes, hooks, and the drill
Lock the reflex levels, walk one decision tree with the answer hidden until you guess, then run the board bank. Tap a reflex card to reveal its level.
The lost-reflex split
A 52-year-old woman has 3 weeks of low-back pain radiating down one leg. On exam, one deep tendon reflex is gone in that leg. The reflex tells you the level. Guess the branch before it opens.
Her ankle jerk is absent on the right. Which root is most likely involved?
Knee jerk gone
Think L4. The patellar reflex is the L2 to L4 reflex, led by L4. Pair it with medial-foot numbness.
Big-toe lift weak
Think L5. There is no single L5 reflex, so L5 shows up as weak great-toe extension and dorsum numbness.
Ankle jerk gone
Think S1. The Achilles reflex is the S1 reflex. Pair it with lateral-foot numbness and a weak push-off.
Knee is L4, you go down on all fours. Ankle is S1, you take one step down. The reflex names the floor.
Hooks that stick
Tap each card to unblur the hook. These are built to survive the test.
See it on real skin
Tap any image to enlarge. Notice how the band ends at the midline in every case.
Shingles · thoracic band
Grouped vesicles in one dermatome. The band stops at the midline.
Shingles · one stripe
One dermatome, one side. The midline is the hard border.
Dermatome map
The full stripe map. Bands, not patches.
Peripheral nerves · hand
Named-nerve patches. These are NOT dermatomes.
The board bank
One vignette at a time. Right-click or long-press a choice to cross it out. Double-click or double-tap to highlight it. Choices and cases shuffle, and nothing repeats until the bank is empty.
Case 1 / 26Sensory mapping
Tip: cross out the answers you have killed, highlight the one you are torn on, then commit.
Medically reviewed by Kaitlyn Cocuzzo, MD and Fatima Ali, DO · Last updated July 12, 2026 at 11:55 PM ET
Bone Wizardry is an independent educational resource for visual learning in the medical sciences. It is not affiliated with, endorsed by, or sponsored by any licensing or examination board, contains no real or recalled examination questions, and does not guarantee any educational or examination outcome.
