Injury or cutting of the transmitting fibers within a nerve due to trauma, leading to the absence of skin sensation and muscle strength.
Nerves can sustain damage from various types of injuries, including cuts from knives, gunshot wounds, penetrative injuries (like those from shattered glass), or accidental contact with powered machinery (such as rotary saws and propellers).
When a peripheral nerve (a nerve outside the brain or spinal cord) is injured and only some of the individual fibers within the nerve are severed, the cut fibers undergo degeneration on both sides of the injury. This results in muscle weakness and a decrease in sensation in the corresponding skin area supplied by those fibers.
When there’s partial severance and the ends of the cut fibers remain in alignment, new fibers can regrow along the pathways created by the degenerated ones. These fresh fibers start to grow within a few days of the injury, although their growth rate is slow, at approximately 1 mm per day.
In cases of complete nerve severance, the individual fibers attempt regeneration. However, lacking guiding pathways, they cluster together to create a lump of tissue. In these instances, functional recovery does not occur.
During the process of nerve fiber regeneration, there are instances where these fibers may mistakenly follow incorrect pathways. As a result, when function is eventually restored, actions could deviate from the intended outcome (such as attempting to move the index finger but also inadvertently moving the middle finger). This can necessitate the relearning of movement skills and the interpretation of sensations.
The nerve pathways within the brain and spinal cord possess distinct structures compared to peripheral nerves. In these pathways, severed fibers do not undergo regeneration. For instance, if the optic nerves are severed, vision cannot be reinstated.
Surgery has the potential to mend a severed nerve, although this option is applicable solely to peripheral nerves. Through microsurgery, the neurosurgeon meticulously aligns and sutures the severed fibers with delicate needles. This meticulous realignment of nerve ends maximizes the likelihood of proper fiber regeneration. Despite the most skillful surgical repair, complete recovery is seldom achieved.
During the recovery phase, a physiotherapy regimen is essential to maintain the health of paralyzed muscles and prevent contractures (abnormal shortening).