Nerve Injuries

Nerves can be thought of as cables which transmit signals from one part of the body to another. Signals which travel towards the brain bring information about touch, pain, heat or vibration. These are called sensory fibres. Signals which travel from the brain carry messages to perform an action such as making a fist. These are called motor fibres.

Some nerves are made up entirely of fibres which pass messages to the brain, and are called sensory nerves. Those nerves composed of fibres which take messages away from the brain are called motor nerves. Most nerves in the upper limb carry both sets of fibres and are called mixed nerves.

The major functions of the hand include performing activities directed by the brain, and receiving information to pass to the brain. In many ways, the hand is merely an extension of the brain, allowing us to touch, feel, grip and hold, and carry out the brain's orders. For this reason, nerve injuries in the upper limb will potentially have a major effect on hand function.

There are 3 main nerves which relate to hand function.

The median nerve is a large, mixed nerve, supplying sensation to the thumb, index, middle and half of the ring fingers, whilst also powering the short, stocky muscles at the base of the thumb. The median nerve is commonly trapped at the wrist in a condition called carpal tunnel syndrome and can be injured when the wrist is cut, or when the wrist breaks.

The ulnar nerve is also a mixed nerve and is found on the little finger side of the wrist. It provides feeling to the little finger and the other half of the ring finger, as well as powering many of the small muscles within the hand itself. Higher up the arm, it runs around the 'funny bone' - explaining why a knock here will make your little and ring fingers tingle. It is commonly trapped as it passes around the elbow in a condition called cubital tunnel syndrome and can be injured after fractures of the forearm or around the elbow.

The radial nerve is a purely sensory nerve by the time it reaches the hand. It does have motor fibres, but these leave the nerve before the level of the wrist joint to supply muscles higher up the arm. It provides feeling to the back of the thumb and can be crushed by a tight wristwatch.

Any nerve can be injured by being cut (for instance when you fall on broken glass), crushed or contused (for instance when you break your arm). Cut nerves can be repaired by careful surgical techniques, often using magnification. The fibres are tiny and can only be sewn together using stitches finer than human hair. Recovery is unpredictable and is rarely complete, except in young children. It is usual to be left with some reduced feeling or muscle weakness/wasting. Recovery in nerves that have been crushed is also unpredictable because it is difficult to be clear exactly what damage has occurred inside the nerve when it is 'trapped'. Even after the nerve has been released, the pace and extent of recovery cannot be predicted.

If nerve recovery is incomplete and sensory function is significantly diminished, your surgeon may discuss a nerve graft operation, but only if the conditions are favourable. If motor function is reduced or absent, other muscles can take over the work, but may need to be moved around the arm in an operation called tendon transfer.

An alternative summary of nerve injuries can be read here