Nerve Injury

Nerve Injury

UNDERSTANDING NERVE INJURY

When a nerve, or group of nerves, in your body has been injured, you may suffer weakness in your arm or leg and numbness of an area of skin. Nerve injuries can also be painful. The first step is to identify which nerve is injured and then which type of nerve injury you suffer from. There are many different kinds and each requires its own treatment approach.

What is a Nerve?

A nerve is like the coaxial cable that you plug into the back of your television. It carries information back and forth between the muscles and the spinal cord the same way a coaxial cable transmits electrical signals from your electrical box to your tv. If you took scissors and cut your tv’s coaxial cable in half, the screen would go blank and if you looked at that cut cable you’d see a group of tiny wires inside.

The interior of a nerve looks the same way; it’s made up of all kinds of little sub-nerves, or fascicles. Within each of those fascicles is a bundle of even smaller units, the actual wires that communicate between the spinal cord and the body - the axon.

An axon is many times thinner than a human hair. The axon is the actual wire that carries electrical impulses from the spinal cord to activate a muscle. These can also carry impulses from the skin, conveying touch from that area of skin back to the spinal cord.

Nerve Damage
When nerves are damaged, the nerve tries to repair itself by sprouting regenerating nerve units. Nerves grow at a rate of about 1 millimeter a day, and if they make the correct connection, then recovery of muscle function or feeling is regained. But if the connection isn’t made correctly, or the nerves have been severed, then recovery will not occur without surgical intervention. It is critical to get the nerve to muscle as quickly as possible, which is why it’s essential that you see a paralysis specialist as soon as possible after a nerve issue has occurred to properly classify your nerve injury.

Common nerves in the arm

Axillary nerve and suprascapular nerve: shoulder movement – these nerves move your shoulder out to the side or in front of your body and rotate it away from your stomach

Musculocutaneous nerve: this nerve flexes the arm at the elbow with the biceps and brachialis muscles bringing your hand up towards your mouth

Radial nerve: This nerve opens the fingers, raises the wrist and extends at the elbow (triceps muscle). Think of reaching out to pick something up.

Ulnar nerve: This nerve provides feeling to the last 2 fingers and is important for hand closing and pinch. This is the “funny bone” nerve and injury to this nerve makes fine movements of the fingers very difficult

Median nerve: This nerve provides feeling to the first 3 fingers and also is important for hand closing and pinch. This provides most of the strength to the thumb, index and middle fingers.

Spinal accessory nerve: This nerve allows you to shrug your shoulders. It also stabilizes the shoulder blade to allow lifting the arm out to the side and over the head Long thoracic nerve: This nerve holds the shoulder blade against the chest to avoid “winging.” When it does not work well, it becomes difficult to raise the arm over the head in front of the body.

Common nerves in the leg

Femoral nerve: This nerve controls the muscles on the front of the thigh and provides feeling on the front and inside of the thigh and leg. This muscle allows you to straighten the leg at the knee or “kick.”

Obturator nerve: This nerve controls the muscles of the inner thigh which brings the legs together.

Sciatic nerve: This nerve is made up of 2 nerves. Tibial nerve: This nerve pushes the foot down at the ankle, curls the toes and turns the ankle in. This nerve also provides feeling to the bottom of the foot.

Common peroneal nerve: This nerve lifts the foot and toes at the ankle and provides sensation to the lateral leg and top of the foot.

Nerve Injury Classification System

When we first meet with a patient at the Paralysis Center, our Specialists’ foremost goal is to properly diagnose the nerve injuries.

They are classified as follows according to the Sunderland and Seddon Classification systems:

• A Sunderland first-degree injury, or Seddon’s neurapraxia, will recover within days after the injury, or it may take up to four months. The recovery will typically be complete with no lasting weakness or problem with sensation. Occasionally a decompression operation is required to ensure this recovery

• A second-degree injury, or Seddon’s axonotmesis, also can recover completely, but in this case the axon is divided and must grow from the site of injury back to the original target. Therefore, the recovery will take much longer than with a first-degree injury as severed axons must regrow at a rate of about 1mm/day or 1 inch per month. The architecture of the nerve is typically preserved and there is not much scar tissue for these axons to navigate. This injury may require a decompression operation on occasion if any impediment to regeneration is present.

• A third-degree injury will also recover slowly and will only partially recover. In this injury there is scarring within the nerve and while some axons get stuck in the scar, others make it through and provide some recovery with time. Recovery is slower and it can be difficult to determine how well these injuries will recover.

• A fourth-degree injury occurs when there is dense scar tissue within the nerve that completely blocks the potential for axons to grow through and make their way back to the muscle. Reconstructive surgery is required for recovery.

• A fifth-degree injury, or Seddon’s Neurotmesis, involves a complete separation of a nerve, such as a with a knife wound where the nerve is divided in two. Reconstructive surgery is required for recovery. Nerves can regenerate, but sometimes require surgical assistance after a peripheral nerve has been injured, it will try and repair itself. When an axon is cut, the part that is no longer connected to the spinal cord essentially disintegrates in a process called Wallerian Degeneration. If the injury is incomplete and any axons are still present, the myelin (or insulation around each axon) is often lost. This myelin loss would block an axon’s ability to communicate with its associated muscle fibers. Thus, even though some axons are present the muscle may still be paralyzed. As a nerve heals, first it will regenerate this myelin to allow those axons to conduct a signal once again.

Those same axons, in the location where they are connected to their muscle fibers, will sprout to connect to the muscle fibers that no longer have their original axon.

This can help recover some strength or all strength depending on how many axons are left. At the same time, the severed axons that maintain their connection to the spinal cord will sprout regenerating nerve units. These will look for an appropriate nerve pathway to grown back down the distal nerve in order to find muscle or skin to connect to.

If they are able to make the journey to an appropriate destination — motor nerve to muscle or sensory nerve to skin — then recovery of muscle function and skin sensation will occur. But if there is an impediment to that regrowth, surgery is required restore an effective pathway. In a situation where a nerve has been cut (a fifth-degree injury or neurotmesis), the nerve ends can sometimes be sewn back together microsurgically. When the area has more extensive or over a length of nerve, a bridge must be utilized, that is when a nerve graft is used. A nerve graft is a piece of “expendable” nerve from another part of the body which is transplanted to the damaged nerve site creating a bridge for the axons to grow through around the region of damage so that they can find their way back to their destination.

In some cases in which sensation or muscle recovery is not anticipated for a very long time because of the great distance from the site of injury to the target or in other cases when the proximal nerve is not available to graft from, a nerve transfer 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. That causes the “donor nerve” axons to now grow to the destination of the nerve that was injured, thus restoring its function.

A neurolysis (or nerve decompression) refers to the removal of scar or compressive structures (including fascia or tendonous edges of muscles) from the nerve and may be undertaken if external impediments (or tight "tunnels") are pinching the nerve, limiting the ability of the regenerating axon to pass through on its way to its target.

Other techniques to restore muscle function, like tendon transfers and free functional muscle transplants, also are covered on our web site.

Schedule a Consult with the Paralysis Center today (844) 930-1001.

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