Peripheral Nerve Injury

How peripheral nerves are built

Each peripheral nerve contains thousands of nerve fibers (axons). Each axon is insulated by myelin and wrapped in connective tissue layers that bundle them together. How badly these layers are damaged determines whether and how a nerve recovers.

Types of nerve injury

A more detailed Sunderland system grades injuries from 1 to 5 based on which layers are disrupted.

Causes

• cuts and lacerations: glass, knives, machinery, surgery
• fractures and dislocations: for example, a broken upper arm damaging the radial nerve, or a hip dislocation injuring the sciatic nerve
• stretch injuries: motorcycle accidents and difficult births injuring the brachial plexus
• compression: prolonged pressure during sleep or anesthesia, tight casts, crossing the legs (peroneal nerve), and entrapment syndromes such as carpal tunnel syndrome
• crush and blast injuries
• injections given into or near a nerve
• burns, electrical injury and radiation

Symptoms

Symptoms follow the area supplied by the nerve:

• sensory: numbness, tingling, pins and needles, reduced feeling of touch or temperature
• pain: burning, shooting or electric pain (neuropathic pain)
• motor: weakness, paralysis, muscle wasting, and specific deformities such as wrist drop or foot drop
• autonomic: dry or sweaty skin, color and temperature changes

Common nerve injuries

Diagnosis

• examination: mapping numbness and testing individual muscles
• Tinel's sign: tapping over the nerve produces tingling at the site of regrowth, and its advance over weeks shows recovery
• nerve conduction studies and electromyography (EMG): most informative about 3 to 4 weeks after injury, when degeneration has occurred. They show the severity and track recovery
• ultrasound and MRI (MR neurography): show whether the nerve is intact, compressed or cut

Treatment

Non-surgical

For neurapraxia and many axonotmesis injuries:

• remove pressure, and protect the limb
• splints to prevent deformity (such as a wrist splint for wrist drop, an ankle-foot orthosis for foot drop)
• physical and occupational therapy to keep joints mobile, maintain muscle and retrain function
• sensory re-education as feeling returns
• nerve pain treatment: medicines such as gabapentin, pregabalin, duloxetine or amitriptyline, and topical treatments
• regular checks for signs of recovery

Surgical

• Direct repair: a cleanly cut nerve is stitched together, ideally within days of injury.
• Nerve grafts: a gap is bridged with a donor nerve (often from the lower leg) or a processed nerve graft.
• Neurolysis or decompression: freeing a nerve trapped by scar or compression.
• Nerve transfers: rerouting a working nerve to a paralyzed muscle, increasingly used for brachial plexus and other severe injuries.
• Tendon transfers: restoring movement when nerve recovery is not possible.

Closed injuries with no recovery on clinical or EMG checks by about 3 to 6 months are usually explored surgically, because muscles that remain without nerve supply for 12 to 18 months cannot recover even if the nerve regrows.

Recovery and outlook

• Neurapraxia: full recovery within weeks to about 3 months.
• Axonotmesis and repaired injuries: nerves regrow about 1 mm a day. An injury 30 cm (12 inches) from the target muscles may take nearly a year to show recovery.
• Better outcomes: children and young adults, clean cuts, early repair, injuries close to the target muscles, and nerves serving a single function.
• Possible long-term effects: reduced sensation, weakness, cold intolerance, chronic pain and, rarely, complex regional pain syndrome.

Frequently asked questions

How long does nerve damage take to heal?

Mild nerve injuries (neurapraxia) usually recover within days to 12 weeks. More severe injuries heal as the nerve regrows about 1 mm a day, roughly 1 inch a month, so recovery can take many months to over a year depending on the distance.

What are the symptoms of nerve damage?

Common symptoms are numbness, tingling, burning or shooting pain, weakness and muscle wasting in the area the nerve supplies. Some injuries cause specific problems, such as being unable to lift the wrist or foot.

Can a damaged nerve repair itself?

Yes, if the outer sheath is intact. The damaged fibers regrow along the sheath. A completely cut nerve cannot reconnect on its own and usually needs surgical repair or grafting for the best chance of recovery.

When is surgery needed for a nerve injury?

Surgery is needed for nerves cut in open wounds, ideally within days. For closed injuries, surgery is considered when there is no sign of recovery on examination or EMG after about 3 to 6 months.

What tests diagnose nerve injury?

Doctors use a detailed physical exam, nerve conduction studies and electromyography (EMG), and sometimes ultrasound or MRI. EMG is most informative about 3 to 4 weeks after the injury.