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 are severed. 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.
If both the nerve and insulation have been severed and the nerve is not fixed, the growing nerve fibers may form a painful nerve scar, or neuroma.
For surgical treatment, the insulation around both ends of the injured nerve is sewn together. The goal in fixing the nerve is to save the insulating cover so that new fibers can grow and the nerve can work again.
If a wound is dirty or crushed, surgery may be delayed until the skin has healed.
If there is a space 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 fix the injured nerve. This may cause permanent loss of feeling in the area where the donor nerve graft was taken.
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.
Source: American Academy of Orthopaedic Surgeons