What is a nerve?
Nerves are part of the “electrical wiring” system that carries messages between the brain and the rest of the body. Motor nerves carry messages between the brain and muscles to make the muscles contract and to move the joint. Sensory nerves carry messages from different parts of the body to the brain carrying signal of pain, pressure, and temperature.
Causes of nerve injury
Nerves are fragile and can be damaged by pressure, stretching, or cutting. Injury to a nerve can stop signals to and from the brain, causing muscles not to work properly, and a loss of feeling in the area innervated by the nerve or pain over the area.
- Pressure or stretching injuries can cause fibers within the nerve to break. This may interfere with the nerve’s ability to send or receive signals, without damaging the cover.
- When a nerve is cut, both the nerve and the insulation(covering) are severed.
Nerve healing and non healing
Sometimes, the fibers inside the nerve break while the insulation remains intact and healthy. If the insulation has not been cut, the end of the fiber farthest from the brain dies. The end that is closest to the brain does not die. After some time, it may begin to heal. New fibers may grow beneath the intact insulating tissue until it reaches a muscle or sensory receptor. Once the new nerve reaches its targets, the muscle will be able to contract or the patient may recover the lost sensation. Generally, the rate of nerve growth is about 1mm per day or about 1 inch per month. But recovery is variable. Unfortunately nerves recover less well as we grow older.
If both the nerve and insulation have been severed and the nerve is not repaired back together, the growing nerve fibers may form an overgrowth “ball” of painful nerve scar called neuroma.
What are the signs and symptoms of a nerve injury?
- Loss or alteration of sensation.
- Loss of muscle power which may result in weakness or total loss of movement eg grip or a feeling of clumsiness.
- Pain. This is variable. Some people notice sensitivity to the cold. Less often gentle touching or stroking of the skin in the affected area may produce an unpleasant feeling.
- Dryness of the skin due to loss of normal sweating.
- Muscle wasting in chronic cases
What is the treatment?
If there is a wound with signs of a nerve injury then an operation will be necessary to look for the nerve and to inspect if it has been partly or completely cut. Cut nerve needs to be repaired.
If there is no wound then it is likely that a “wait & see” policy will be adopted. Further investigations such as nerve study may be carried out to try and assess the damage to the nerve. The patient will be examined regularly for spontaneous nerve recovery. If nerve recovery is not happening, then surgical treatment is required. The area of suspected nerve injury will be explored and the nerve inspected for injury. The scarred portion of the nerve will be excised and the gap bridged with a donor nerve taken from another part of the body.
There are several methods of nerve surgery that the microsurgeon will use to heal the injured nerve.
The covering (insulation) around both ends of the injured nerve is sewn together. The goal in fixing the nerve is to ensure continuity of the insulating cover so that new nerve fibers can grow within to reach its targets and the nerve can work again.
If there is a gap between the ends of the nerve, it may be necessary to take a piece of nerve (nerve graft) from a donor part of the body to bridge the gap of the injured nerve. This is called nerve grafting. This may cause permanent loss of feeling in the area where the donor nerve graft was taken.
Nerve transfer (neurotisation)
A nerve transfer is a surgical technique that may be used when a patient has a nerve injury. Nerve transfers involve taking nerves with less important roles — or branches of a nerve that perform redundant functions to other nerves — and “transferring” them to restore function in a more crucial nerve that has been severely damaged. The surgeon will use functioning nerves that are close to the target muscle or sensory area, and these nerves are transferred or “plugged in” to the injured nerve that no longer functions. The nerve that has been “plugged in” now supplies that function. For example, if a breathing nerve is used to restore elbow flexion, the patient may initially have to take a deep breath to move the arm. The brain then learns this trick and soon the patient is able to move the arm simply by thinking about moving the arm. Motor nerves are used to re-innervate muscles and sensory nerves are utilized to restore sensation. This technique provides a nearby source of nerve for faster recovery
Nerve recovery after repair
Once the insulating cover of the nerve is repaired, the nerve generally begins to heal three or four weeks after the injury. Nerves usually grow one inch every month, depending on the patient’s age and other factors. With an injury to a nerve in the arm above the fingertips, it may take up to a year before feeling returns to the fingertips. The feeling of pins and needles in the fingertips is common during the recovery process. While this can be uncomfortable, it usually passes and is a sign of recovery.
Rehabilitation and therapy
Several things can be done to keep up muscle activity and feeling while waiting for the nerve to heal.
- Physical therapy will keep joints flexible. If the joints become stiff, they will not work, even after the muscles begin to work again.
- If a sensory nerve has been injured, care must be taken not to burn or cut fingers because there is no feeling in the affected area.
- With a nerve injury, the brain may need to be “re-educated.” After the nerve has recovered, sensory re-education may be needed to improve feeling to the hand or finger.