Nerves connect your brain and spinal cord to the muscles and skin, giving you movement and feeling. If a nerve injury occurs, there is an interruption in the information being conveyed to the skin or muscles to and from the brain. The larger nerves in your arms and legs, which are about the size of a pencil, are made up of tens of thousands of nerve fibers — similar to the makeup of a telephone cable. The nerve fibers are grouped together in bundles called fascicles. Some nerves — such as the median and ulnar nerves in your arm — have motor and sensory fascicles, giving you both movement and feeling in your hand.
A nerve injury can result in a problem with a muscle or in a loss of sensation. In some people, it also causes pain. To understand nerve injury and recovery, it is important to understand the different types of nerve injury. The type of nerve injury will determine the type of treatment that will be needed.
Nerve Recovery and Regeneration
After nerve injury, the nerve will try to repair itself by sprouting regenerating nerve units. These regenerating units will then try to grow down the nerve to reinnervate (restore nervous function to) muscle or skin. If they make a correct connection — motor nerve to muscle or sensory nerve to skin — then recovery of muscle function and skin sensation will occur. However, if the regenerating nerve fibers do not make a correct connection, then no recovery will occur.
Nerves regenerate at the rate of one inch per month. Although sensation can be regained even after long periods of denervation (loss of nerve supply), muscle reinnervation will not occur after long periods of time without nerve innervation (nerve supply). Therefore, it is necessary to get nerve to muscle as quickly as possible if recovery will not occur on its own. Electromyography (EMG) tests will show muscle recovery before the muscles can be seen contracting. If there is no evidence of recovery by three to six months after nerve injury, surgery usually is recommended.
If surgery is necessary, there are several types of surgery that may be recommended. These include nerve repair, nerve graft, nerve transfer or neurolysis.
For nerve regeneration, the regenerating nerve fibers need the guidance of the nerve for direction to the muscle or sensory unit. If the nerve has been cut, a nerve repair is used to sew the two ends of a nerve together. This usually is possible when the nerve has been cut sharply. However, in cases with more extensive damage, it may not be possible to sew the two ends of the nerve directly together once the damaged nerve has been trimmed away.
In these cases, a nerve graft is used. A small piece of donor nerve is used to bridge the gap between the two nerve ends, and the nerve then will regenerate across this “bridge” to provide recovery. The donor nerve is taken from other areas of your body using small, non-critical, sensory nerves. Depending on how much donor nerve graft is needed, several nerves are commonly used; these include the sural nerve in your leg and the medial antebrachial cutaneous nerve in your arm. The sural nerve runs up the back of your leg, and the surgery will leave you with a scar in the back of your leg and with numbness to the outside of your foot. The medial antebrachial cutaneous nerve is taken from your inner upper arm, and this procedure will result in numbness to the inside of your forearm. After surgery, you will have a large area of numbness in the region of the donor nerve that will become smaller over several years. As this donor area gains sensation, you may feel more tingling in the area of numbness.
In some cases in which sensory or muscle recovery is not anticipated for a very long time, nerve transfers may be used. Nerve transfers use functioning nerves that are close to the target muscle or sensory area, and the nerves are transferred to the injured nerve. This provides a close source of nerve for faster recovery.
A neurolysis refers to the removal of scar from the nerve and may be used if scar tissue is blocking the nerve from regenerating.
Complications from surgery include infection, bleeding and delayed wound healing of the primary surgical site or the donor nerve site in cases of nerve graft. Since this type of surgery involves nerves, there is a risk that your nerve function in the region of your injury – with respect to sensory or motor function – will be lessened, or pain may develop.