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Which Fingers Are Numb Is the Best Clue You’ve Got. Here’s How to Read It.
Thumb, index, middle and the thumb-side half of the ring finger: median nerve. Little finger and the other half of the ring finger: ulnar nerve. The back of the hand on the thumb side, especially the web between thumb and index: radial nerve.
Three nerves run into your hand, and each one owns a specific territory of skin and a specific set of muscles.
So the fingers that go numb are not random information. They are the single most useful diagnostic fact you can bring to an appointment. Knowing which territory you have narrows the list from twenty conditions to about three.
Get it wrong and you can spend months treating the wrong spot. A night splint on the wrist does nothing for a nerve pinched at the elbow. Wrist surgery does nothing for a nerve root in the neck. Meanwhile the nerve that IS squeezed keeps losing ground.
Below: each nerve’s territory, where it gets squeezed, a one-minute self-test for each, how long nerves take to recover, and when numbness needs to be seen today.
Which nerve supplies the thumb, index and middle finger?
The median nerve.
- Skin: palm side of the thumb, index, middle, and the thumb-side half of the ring finger. Plus the backs of the fingertips of the index, middle and that half of the ring finger.
- Muscles: most of the muscles that bend your fingers, plus the pad of muscle at the base of the thumb that lifts it up away from the palm.
- Where it gets squeezed: at the wrist, in the carpal tunnel. Higher up in the forearm, as pronator teres syndrome.
- The distinguishing detail: the nerve gives off a branch to the palm BEFORE the carpal tunnel. So carpal tunnel numbs the fingers but usually spares the palm. A numb palm as well points higher up the arm.
Which nerve supplies the ring and little finger?
The ulnar nerve.
- Skin: little finger and the little-finger half of the ring finger, front and back, plus the edge of the hand.
- Muscles: nearly all the small muscles inside the hand, the ones that spread your fingers, pinch strongly and do fine coordination. This is why ulnar problems cost you dexterity and grip, not just feeling.
- Where it gets squeezed: at the elbow, in the cubital tunnel, which is by far the commoner site. At the wrist, in Guyon’s canal, often in cyclists.
- The distinguishing detail: the nerve gives a branch to the back of the hand before the wrist. Numbness on the BACK of the little-finger side of the hand means the problem is at the elbow, not the wrist. That single observation sorts most ulnar cases.
The ring finger is split down the middle between two nerves. Which half is numb tells you which nerve, and it’s a question almost nobody gets asked.
What does the radial nerve supply in the hand?
- Skin: the back of the hand on the thumb side, especially the web between thumb and index. No palm territory at all.
- Muscles: everything that straightens the wrist, the knuckles and the thumb. In the hand, it bends nothing.
- Where it gets squeezed: in the upper arm, producing a wrist drop (the classic is falling asleep with an arm hooked over a chair). In the forearm as radial tunnel syndrome, or as the motor-only PIN palsy. At the wrist, as Wartenberg’s syndrome, with a tight watch strap the classic cause.
For how these nerves serve the thumb in particular, see thumb anatomy.
How can I tell which nerve is affected? Three one-minute tests
- Median. Make an OK sign with thumb and index. A flattened, pinched-looking circle instead of a round one means a deep forearm branch of the median nerve is affected. Then look at the thumb pad from the side, both hands together. Flatter on one side is a finding.
- Ulnar. Hold a piece of paper between your thumb and the side of your index finger while someone pulls. If your thumb tip bends to hold on, that’s compensation for ulnar weakness. Also check whether your little finger drifts away from the ring finger and won’t tuck back in.
- Radial. With the forearm supported palm-down, lift the wrist and fingers up against gravity. Can’t, or the fingers lag while the wrist lifts? Radial nerve.
I test all three on every new nerve patient, on both hands, before I touch a single tunnel. It takes a minute and it stops you treating the wrong nerve.
When the numbness doesn’t fit the map
If the numbness doesn’t follow any of these territories, the problem probably isn’t a single nerve in the arm.
- Numbness in a stripe running down the whole arm. A nerve root in the neck, not the hand. See cervical radiculopathy.
- All fingers, both hands, symmetrical, glove-like. A generalized neuropathy, which is a medical workup rather than a hand one. See peripheral neuropathy vs carpal tunnel.
- The whole hand, after an injury, with burning pain and color change. Think CRPS.
- Ring and little finger plus the inner forearm, worse with arms overhead. Consider the nerves at the base of the neck. See thoracic outlet syndrome.
Still unsure which fingers are which? The symptom-first version is pins and needles in your fingers: which nerve.
How are nerve problems in the hand diagnosed?
- The map. Which fingers, which surface, palm involved or not, night or day, constant or coming and going.
- Provocation tests. Tapping over the nerve (Tinel’s), holding the wrist bent (Phalen’s), or the elbow fully bent for a minute to load the ulnar nerve. Reproducing your tingling in your territory is the point.
- Sensation testing. Light-touch filaments and two-point discrimination give a number for how much feeling you’ve lost.
- Strength. Pinch and grip measured on a gauge, compared side to side.
- Nerve conduction studies and EMG. Measure how fast and how well the nerve carries a signal, and whether muscle has lost its supply. See nerve conduction test results explained.
- Ultrasound or MRI. Sometimes, to see a swollen nerve or what’s pressing on it, such as a ganglion.
How long does a squeezed or cut nerve take to recover?
Nerves heal on their own clock, and this is where the Closing Window Method earns its keep. The window is the time before the muscle that nerve feeds gives up waiting.
- Comes and goes, mostly at night (window OPEN). The nerve is irritated, not damaged. Take the pressure off and it often settles over weeks. Give a night splint about 6 weeks before judging it.
- Numb all the time (window CLOSING). The nerve is losing ground. Release still helps, but recovery after surgery is slower and may be incomplete. See still numb after carpal tunnel surgery.
- Muscle wasting (late in the window). A flat thumb pad, or a hollow between thumb and index on the back of the hand. The goal shifts from full recovery to stopping it getting worse. Wasted muscle can take a year or more to rebuild, and in long-standing cases may not fully return.
- Cut and repaired. After a lag of a few weeks, a repaired nerve regrows at roughly 1 mm a day, about an inch a month. A wrist-level repair can take many months to reach the fingertips, and adult feeling rarely returns to perfect. Muscles need to be reached within roughly 12 to 18 months or they stop accepting the nerve. See nerve repair recovery.
What helps while you wait to be seen?
- Take the pressure off. Wrist neutral at night for the median nerve (carpal tunnel night splint). Elbow not fully bent at night for the ulnar nerve (cubital tunnel night splint, or a towel wrapped loosely around the elbow). No leaning on the elbow at a desk or car door.
- Nerve glides. Gentle, slow, never stretched into strong tingling. 5 to 10 reps, 2 to 3 times a day. See nerve glide exercises.
- Protect numb skin. If you can’t feel well, you can’t feel a hot pan, a sharp edge or a blister forming. Check your fingers after cooking and tool work.
- Splints for weakness. A wrist drop splint for radial palsy, an anti-claw splint for ulnar weakness. They keep the hand usable and the joints supple while the nerve recovers.
- Work and driving. Most people keep working with intermittent tingling. Constant numbness and a weak pinch change that: dropping tools, fumbling small parts, or a grip on the wheel you can’t trust are all reasons to get assessed before you push on.
Go to the emergency department now if
- Numbness or weakness came on suddenly in one arm with a drooping face, slurred speech, or weakness in the leg on the same side. That’s a possible stroke. Call emergency services.
- Numbness in both hands with new trouble walking, or with loss of bladder or bowel control.
- Numbness with severe, escalating forearm pain and tightness after an injury or in a cast, especially pain on stretching the fingers. See acute forearm compartment syndrome.
Get it checked today if
- A cut on the hand, wrist or finger has left any part numb. Cut nerves do best repaired early, ideally within days.
- Numbness after a wrist fracture or in a cast is getting worse rather than better. See numb fingers after a wrist fracture.
- You woke up unable to lift the wrist or fingers.
Get it checked if
- Numbness has become constant rather than coming and going.
- The thumb pad looks flatter, or a hollow has appeared between thumb and index on the back of the hand.
- You’re dropping things or fumbling buttons.
- Night numbness has been waking you for more than a few weeks. See hands numb at night.
- The numbness doesn’t fit any of the maps above.
Before your appointment, work out exactly which fingers and which surfaces are affected, and whether the palm is involved. That single sentence does more diagnostic work than any scan.
Written by Nigel Chua, hand occupational therapist in practice since 2005. Thousands of hands, wrists and elbows assessed and treated. My credentials are here. This article explains; it doesn’t examine. Numbness that’s become constant, or a muscle that’s started to flatten, deserves a proper assessment this week.