The nervous system is like a massive communications network, carrying signals from the brain to the rest of our body.
The central nervous system (CNS) is comprised of the nerves in the brain and spinal cord, and the peripheral nervous system (PNS) reroutes the signals from the CNS to the appropriate muscles and organs. Motor nerves take the signal to the target limb or organ, and sensory nerves carry messages back to the CNS, where the brain can process them.
These signals are responsible for every function you take, whether involuntary (blinking) or voluntary (clicking on the link to read this blog post).
For another metaphorical example, think of a downed electrical wire on your street. It can cut off communications and power to your house. So can you just imagine what happens to your body when a nerve is not just injured, but severed?
Anatomy of a Nerve
The cells of our nervous system, called neurons, transmit signals through fibers called axons. These axons are wrapped up in fatty, electrically conductive tissue that speeds up the signals to the muscles and organs. This covering is called the myelin sheath.
Generally, if either the fibers or the myelin sheath is injured, recovery is fairly straightforward, if time-consuming. For instance, compression or stretch injuries to the peripheral nervous system can cause fibers within the axon to break, but without damaging the myelin sheath. This is often the situation in the least serious form of nerve injury, neurapraxia, where damage temporarily blocks the signals from going through properly. More severe is axonotmesis, where the injury causes the surrounding nerve endings to degenerate, and healing may take months or even years.
In a transvection injury, though, the nerve is severed, and both the fibers and the sheath are broken. This is the worst type of nerve injury. Typical causes of transvection injuries include knife wounds, gunshots, car accidents, or a hyperextended limb.
This injury is especially problematic if it happens to the dorsal nerve root, which collects and relays the sensory nerves’ messages to the CNS. If the dorsal root of a spinal nerve is severed, the patient will likely feel pain, numbness, or a burning sensation along the affected nerve.
Nerve Recovery and Regeneration
If the sheath somehow remains intact, the end of the axon farthest from the brain dies, like the broken tail of a lizard. However, the other end of the axon is still connected to the CNS and may, after some time, begin to grow new fibers. It’ll use the myelin sheath as a guide until it reaches a muscle or sensory receptor.
If it makes a correct connection, that will result in eventual recovery of muscle function and sensation. If it doesn’t make a correct connection, then no recovery will happen.
If the nerve has been completely severed, meaning that the myelin sheath is broken, surgery is likely necessary.
Surgical Treatment of Severed Nerves
The first step in surgical nerve repair is to explore the injured nerve and remove any injured tissue from the nerve endings. Depending on the injury, there may be enough length to directly reconnect the two ends.
From a repair standpoint, though, it’s only surgically possible to repair the myelin sheath, not the nerve fibers. Fixing the sheath, however, enables the nerve to regrow the broken fibers.
If there isn’t enough material left to connect the ends of the nerve, a nerve graft may be necessary, where the non-essential nerve is taken from a different part of the body (usually from the leg or upper arm) and used to connect the nerve endings.
The main drawback of this approach is that it may cause permanent loss of feeling in the area where the donor graft was removed.
For instances where a graft isn’t an option, the use of a nerve conduit – an artificial tube that connects the nerve endings – may be possible.
Once the sheath is repaired, the nerve generally begins to heal within several weeks.
It’s a long process, though: Nerves typically grow only one inch per month. Depending on the location of the nerve injury, sensation might not return for a year.
Doctors and patients can track the progress of recovery by tapping a sensitive area within the reconstructed nerve. It should tingle. That means the nerve fibers are regrowing.
You will need a number of periodic checkups to keep an eye on these regenerating fibers, followed by physical therapy and, eventually, strengthening exercises.
Later, as sensation returns to the area, the physical therapy will focus on regaining a sense of touch.
It’s important to keep in mind that even after a successful repair of a severed nerve, there likely will be a residual, permanent loss of function in the area.
Here are some other tips to consider:
- During recovery, be sure to keep the injured area away from heat or sharp objects, since there’s no feeling of pain to warn you.
- Don’t skimp on physical therapy. Not only will it help keep the joints flexible and restore strength, it’ll also reduce the risk of scar tissue on the fixed nerve.
- Depending on the extent of damage, some sensory re-education might be required. Your brain is working with what is essentially a new nerve, so it may need some training to improve motor control or sensation.
Getting to the Finish Line
Recovering from a severed nerve is hard – and it’s unlikely that full sensation or mobility will ever return. But the human body continues to surprise us, and new procedures are discovered constantly. With determination, support, and luck, you can stand tall.