The recovery of the nerve is a complex process that has its peculiarities, being different to other tissues of the body. We have all suffered a skin wound and we have seen how the body in a matter of days is healing. If we take a hit, we are sore for a short time and it happens to us. When we suffer a nerve injury, however, our doctor tells us that it will take months to recover. Why is this happening?
How is the nerve root damaged?
Nerve roots coming out of the neck and back can be damaged in several ways:
– Compression. A structure that is close to the nerve compresses the nerve and injures it. This is typical of a herniated disc or an osteophyte (an extension of bone that forms in a wear zone). This is most common in the column.
– Traction. If a nerve is anchored in a point and we pull it, we can damage it. When there is a root entrapment, if we perform an abrupt stretching of the hamstrings, for example, we can damage the nerve root by a traction mechanism.
– Ischemia. We call this the mechanism by which a tissue undergoes damage when the blood does not reach it well. In the compression and tensile mechanism there is also a component of damage due to ischemia. When a tissue does not reach the blood well, it dies. This is what we call infarction. This process is well known when it occurs in the heart.
– Inflammatory processes such as that caused by a viral infection or an autoimmune process.
– Metabolism. Diseases such as diabetes can damage the nerve and produce symptoms.
What can happen to the nerve root?
The nerve root that comes out of each area of the back is like a wire full of nerve fibers. Each “hair” of the cable is the axon of a neuron.
Let’s look at the picture. This hair that comes to the body of the neuron is the axon and is the one that will transmit the nervous signal. The body of the neuron is the one that feeds the axon. If we cut the axon, only the part that is not attached to the body is killed. This death is called Wallerian degeneration. It would be like cutting off the tail of a lizard, the tail will die and the lizard will regenerate the tail that was cut off.
The nerve root is all these axons or nerve fibers together in the form of cable. In a compression, for example, some or all of the nerve fibers that make up the nerve root may die.
The nerves that leave the lumbar or cervical area contain fibers of different sizes and with different functions. The smaller fibers carry information about pain and sensitivity. Typically, these smaller fibers are initially affected and pain and sensitivity changes are noted. In more serious injuries we will have muscular involvement due to the injury of the fibers that carry the signal to the muscle.
Sometimes no nerve fibers die and only the root myelin sheath is damaged. Myelin is a layer that needs the nerve to function properly and that mainly gives speed to the signal conduction. In these cases, the nerve does not work well but there is no damage to the structure of the nerve fibers that compose it. It would be the mildest injury where the symptoms will be temporary and the recovery will be complete upon referral of the cause.
How and when does nerve recovery occur?
The star questions when we suffer from a nerve root injury are two: “Will I recover?” And how long does nerve recovery take? This depends on the situation of the injury and the mechanisms that the nerves use to recover.
The main thing for nerve recovery is that we stop the mechanism that is damaging it. For example, if we have a hernia compressing a nerve root and we operate, the nerve will stop being compressed. At other times will be medicines like corticosteroids or the healing process of our own body that will remove the threat. Once the cause is removed, the nerve root can start its recovery mechanisms.
1 – The slightest situation occurs when there is damage in the myelin without injury to the nerve fibers. In this case two phenomena occur. On the one hand the driving is blocked and does not pass the signal correctly by this point. The nerve stops working but temporarily. This blockage gives way quickly and then all that is left is for the nerve to repair myelin. This can take from weeks to months to recover depending on the degree of involvement.
2 – If there is death of some of the fibers of a nerve there are two mechanisms that try to solve the problem:
– On the one hand, the part that has not died of the axon begins to grow and crosses the area of the injury. It does so at a rate of a few millimeters per day or so (this all depends on the type of injury and the location). As they grow, they may come to the place where they should or go to the wrong place. If the axon has to grow and travel long distance it will take longer and it is easier to get lost along the way.
– On the other hand, the fibers of the nerve that are healthy, in their destination (in the muscle for example) begin to grow to encompass more territory than theirs. Imagine an area of the muscle that does not reach a sign of any nerve. The nerves of the healthy areas grow their nerve endings to try to take charge of this area of muscle to which no signal arrives. This expansion contributes to the improvement although it has a relative level of effectiveness.
Responding to the questions asked, if there is no damage from the axons the nerve recovery will be quick when the cause gives in. In cases where there is little axonal damage and, above all, myelin damage, it may take a few months but a faster recovery is seen with progressive changes to improvement. There is a steady evolution towards improvement. In the first 3-4 months almost all the lost force will have recovered. When a significant number of axons die, repair mechanisms need many months to produce improvements in sensitivity and function. We would be talking about periods of 8-12 months to see a situation of sequelae that will surely be in this case.