Peripheral Nerve Injury

An injured nerve regrows at approximately one millimetre a day, or an inch a month 1. From an injury at the wrist, axons must regrow about 100 mm to reach many of the hand muscles, so recovery takes at least 100 days 1.

This makes the timeline predictable, which matters: a family told 'we will see' worries differently from one given a specific expected timeframe for the first signs.

Muscle that has been denervated for too long undergoes irreversible change, and after roughly 12 to 18 months reinnervation produces little useful function even if the nerve arrives 1.

This is why surgical decisions — repair, grafting or nerve transfer — are time-critical, and why a nerve injury that shows no recovery at the expected point needs surgical review rather than continued waiting.

Maintains joint range so contracture does not develop, protects insensate skin from injury and burns, prevents overstretching of paralysed muscles through splinting, and keeps the rest of the limb conditioned.

Electrical stimulation is used to maintain muscle where voluntary contraction is absent. Sensory re-education begins as sensation returns, because a hand that feels inaccurately is used poorly even when it is strong.

Radial nerve injury from a humerus fracture causes wrist drop and usually recovers: in a systematic review of 1,045 patients, 88.1% recovered overall, and 70.7% of those managed without surgery recovered spontaneously 2. Ulnar nerve injury at the elbow affects grip and fine control. Peroneal nerve injury at the knee causes foot drop and is managed with an ankle-foot orthosis while it recovers.

Brachial plexus injuries are a larger category and are covered separately, in adults after trauma and in newborns after difficult delivery.

A regenerating nerve grows at roughly a millimetre a day 1. The muscle it is heading for remains reinnervatable for a limited period — commonly described as around twelve to eighteen months — after which it is replaced by fibrous tissue 1.

This is why the distance from injury to muscle can be measured and turned into a timetable, and why surgical decisions cannot be postponed indefinitely while waiting for spontaneous recovery.

Joint range, because a joint that stiffens during the wait cannot be used when the nerve arrives. Skin, in an area that cannot feel. Muscle bulk, with electrical stimulation where it is appropriate.

And function in the meantime, through splinting and trained compensation — a hand that cannot extend the wrist can still work with the right splint, and waiting passively wastes months.

Age, which nerve is injured and the delay before repair all affect the result. In a pooled analysis of individual data on 623 median and ulnar nerve injuries repaired with microsurgery, people under 16 had 4.3 times the odds of a good motor recovery compared with people over 40 3. Each month of delay before repair lowered the odds of a good motor and sensory recovery 3.

Ulnar nerve injuries did worse than median ones: the chance of motor recovery was 71% lower 3. That is why the expected result is discussed openly at the start, and why an injury that needs surgery is not left to wait.