Digital Nerve Injury

Anatomy of the finger nerves

Each finger and the thumb has two main digital nerves running along the palm side, one on each side, close to the arteries. They branch from the median nerve (thumb, index, middle and half the ring finger) and the ulnar nerve (the other half of the ring finger and the little finger). They carry touch, pain and temperature sensation, which is essential for grip, fine control and avoiding injury.

Because they lie just under the skin, even a modest cut on the palm side of a finger can sever a digital nerve.

Causes

• Cuts (lacerations): kitchen knives, broken glass, box cutters, power tools and sheet metal
• Crush injuries: doors, machinery
• Bites
• Surgery on the finger or palm
• Compression: from bowling thumb (a perineural fibrosis of the thumb nerve), tight rings or repetitive pressure, which cause gradual numbness rather than sudden loss

Symptoms

• numbness on one side of the finger, from the cut to the tip
• tingling or "pins and needles"
• reduced ability to feel temperature or sharp objects on that side
• clumsiness with fine tasks
• loss of sweating on the affected side, so the skin may feel smoother
• later, a tender lump at the injury site (neuroma) if the nerve was not repaired

If the cut also severed a flexor tendon, you will not be able to bend the finger at one or both joints. If the digital artery is cut, the finger may be pale or bleed heavily, although each finger has two arteries.

Diagnosis

A doctor or hand surgeon will test sensation before numbing the finger:

• Light touch and two-point discrimination: the ability to tell two points apart, normally less than about 6 mm on the fingertip
• Sharp vs blunt testing
• Sweat test: absent sweating on the injured side
• Tendon and circulation checks

Exploring the wound in an operating room is often the only way to confirm a cut nerve. Ultrasound can help in some cases.

Treatment

Surgical repair

Cut digital nerves are repaired by a hand surgeon, ideally within a few days of injury, using a microscope and very fine stitches to join the nerve ends (neurorrhaphy). If there is a gap, the surgeon may use a nerve graft, a nerve conduit (tube) or a processed donor nerve. Tendon and artery injuries are repaired at the same time.

Some surgeons do not repair very distal nerve cuts near the fingertip, where results without repair can be similar. Decisions depend on the location, the finger and your needs.

Non-surgical care

Nerves that are bruised or stretched rather than cut usually recover on their own over weeks to months and are monitored.

After surgery

• a splint protects the repair for about 3 to 4 weeks, often keeping the finger slightly bent
• hand therapy restores movement and later sensation
• sensory re-education retrains the brain to interpret new signals, using textures and objects
• desensitization reduces hypersensitivity using graded textures and tapping

Recovery time

Nerves regrow at about 1 mm per day, or roughly 1 inch (2.5 cm) a month, after a delay of a few weeks. Tingling that moves toward the fingertip (Tinel's sign) shows the nerve is regrowing.

Most adults regain useful protective sensation within 6 to 12 months, though feeling is often not completely normal. Cold sensitivity is common for the first year or two.

Complications

• incomplete return of sensation
• painful neuroma
• cold intolerance
• stiffness, especially if a tendon was also injured
• complex regional pain syndrome, rarely

For general care of the wound itself, see open wound of the finger.

Protecting a numb finger

Until feeling returns, protect the finger from burns, cuts and cold: use oven gloves, check water temperature with the other hand, and look at the finger often for wounds you did not notice.

Frequently asked questions

How do I know if I cut a nerve in my finger?

The main sign is numbness or tingling along one side of the finger beyond the cut, often reaching the fingertip. You may notice reduced feeling to light touch, temperature or sharp objects. Any numbness after a cut should be checked by a doctor the same day.

Does a cut digital nerve need surgery?

Usually yes, especially for cuts between the palm and the last joint of the finger. Repair within a few days gives the best chance of recovery. Very small branches near the fingertip are sometimes left to heal without repair, depending on the surgeon's assessment.

How long does a digital nerve take to heal?

Nerves regrow about 1 mm a day, so it can take 3 to 12 months for feeling to return to the fingertip. Recovery is often incomplete in adults, and cold sensitivity can last for a year or more.

Will feeling come back if a finger nerve is not repaired?

Some feeling may return from nearby nerves, but an unrepaired cut nerve often leaves permanent numbness and can form a painful neuroma. Late repair or grafting is still possible, so see a hand surgeon if you have ongoing numbness after a cut.