The nerves act like the wires in the body's "telephone system" and carry messages between the body and the brain. There are two types of nerves. The first type, the motor nerves, carry information from the brain to the muscles and are used to make the muscle (and the body) move. The second type of nerve is a sensory nerve. Sensory nerves are used to carry messages back and forth from the body to the brain to indicate pressure, pain, and temperature.
Makeup of Nerves
The nerves are wrapped up in insulation, in this case with a layer of surrounding tissue that protects the nerve from injury. Each individual nerve is made up of millions of individual fibers that are bundled together inside the insulating tissue. While each particular nerve fiber, or axon, works as either a motor or sensory nerve, most nerves are made up of both types in the human body.
Results of Injury
The nerves that serve the body aren't particularly strong, and they can be injured or broken from too much stretching, pressure, or cutting. If the nerve is damaged through excessive stretching or pressure, it may stop working and no longer carry messages to and from the brain. The tissue surrounding the nerve, however, may be undamaged. If the nerve is cut, the nerve along with its covering may both be broken. In any injury, the nerve's ability to carry messages may be interrupted, and this can stop muscles from working or can cause loss of feeling in the part of the body served by that particular nerve.
If a nerve fiber breaks, the end of the nerve that's farthest from the brain dies. If the insulation isn't damaged, it becomes an empty tube once the nerve completely dies. The end of the fiber closest to the brain will not die, however. In fact, it may even start healing on its own, possibly growing back through the uninjured tube until it reaches a muscle or a sensory receptor.
If both the nerve and its surrounding tissue are cut and the nerve is not repaired, a condition known as a neuroma may result. In such cases, the nerve fibers try to grow back but because they don't have a good insulating tube in which to grow, they end up forming a ball at the site of the original cut. The neuroma that results can be painful and can even cause an electrical sensation when it's touched.
Treatment of Nerve Injuries
If the injury caused a cut in both the nerve and its insulation, the insulation needs to be carefully sewn back together so the nerve can grow back on its own. Since nerve fibers, especially those that serve the fingers, can be as tiny as a strand of thin spaghetti, the hand surgeon needs to make the stitches very thin and tiny. Because the repaired insulation is so fragile, a splint may need to be worn for the first three weeks to hold it in place until it begins healing. Since the nerve will attempt to grow back down the tube on its own until it reaches a muscle or receptor, the hand surgeon just focuses on repairing the insulating tissue (figure 2).
During the surgery, your hand surgeon will line up the ends of the empty tube and all the fibers it holds as closely as possible. There are millions of nerve fibers in the bundle, however, and some of the original connections may not grow back perfectly. If the area near the wound was crushed or has skin that needs to grow back, your hand surgeon may delay surgery focused on repairing the nerve until the other damage has healed.
If the injury ended up causing a gap between the ends of the nerve or its insulation, the hand surgeon may need to perform a nerve graft to fill the opening by taking a tiny piece of nerve from somewhere else in the body. This graft will return feeling and movement to the injured finger or area, but it may end up leaving the part of the body the nerve served losing its sensation. If the gap is small enough, however, the missing insulation can sometimes be replaced with a special cylinder or even with part of a vein.
After the insulating tissue is repaired, it will take three to four weeks for the nerve fibers to grow back across the site of the injury. The fibers will grow back down the tubes at about an inch a month, so if the injury was in the forearm a foot or so from the fingers, it may take a year before feeling in the fingertips return. During this time, it's common to have a "pins and needles" sensation in the tips of the fingers; while this sensation is mildly uncomfortable, it is a good sign of healing.
It may take months for a nerve to heal after treatment, and during this time your hand surgeon may want you to keep the joints flexible through physical therapy. If the joints are allowed to become stiff, even after the nerves that control the muscles return, it may be impossible to move your fingers or whatever area of the body was affected. During the recovery period, if a sensory nerve was damaged, extra care must be taken about cuts and burns. Since the fingers or other area don't yet have any sensation, it's possible to injure the area without knowing it.
Even after the nerve grows back, due to a prolonged disconnection between the brain and the nerve, the brain may simply ignore the nerve. To treat this, the brain may need to be re-educated to respond to the nerve, and your doctor might suggest some specific therapy to accomplish this.
In some cases, full recovery is not a possibility. This may be due to factors such as the nature of the wound, its location, and the age of the person who suffered the injury. Even if the injury caused permanent loss, therapy and care by one of our very skilled hand surgeons may produce really positive results.