Where is the radial nerve and what does it do?

The radial nerve runs down the back of the upper arm and runs along the humerus bone before passing into the forearm. It is connected to both muscles (movement) and skin (sensation).  It is responsible for triceps (elbow extension) as well as the muscles that extend the wrist , fingers, and thumb.  Most of us think about the biceps muscle as the main muscle that flexes the elbow.  The radial nerve is also connected to an important muscle that also contributes to flexing the elbow called brachioradialis. The skin connects through the radial nerve to the brain with sensation information from the back of the forearm and hand mostly.

What causes a radial nerve palsy?

The radial nerve travels along the humerus bone in the upper arm.  When there is prolonged pressure to the back of the arm the nerve has no cushioning to protect it. The nerve becomes squished directly against the bone. Brief pressure is well tolerated but sustained pressure damages the nerve at this site where it is vulnerable.

In medical textbooks this is often called “Saturday night palsy”. This is because of the association of someone being intoxicated with alcohol and falling asleep with their arm over the side of a chair leading to this nerve damage. Usually when we sleep we will toss and turn to some extent or be woken up by discomfort.  When someone is in an intoxicated sleep from alcohol, recreational, or prescription drugs they often don’t move or respond to discomfort. While the classic means of nerve injury is sleeping in a chair with the arm draped over the side, it can also happen by simply sleeping with your arm hanging off the bed with pressure over the triceps area. Rarely it can occur in other situations like pressure on the nerve from the inside part of the arm of a chair from prolonged sitting.

What are the symptoms of a radial palsy?

The usual story is someone waking up having lost the ability to extend the wrist and fingers. As the triceps muscle is already connected before the spot where the nerve is damaged, ability to extend the elbow is unaffected. While patients can still flex the elbow due to a functioning biceps, there is some weakness of elbow flexion as the brachioradialis has been weakened.

This is very frightening as some people will have gone to the emergency room thinking that they have suffered a stroke.

Radial palsy is most often a problem of pure weakness.  There is no pain. Usually there is no numbness or tingling but some people can have mild sensation changes along the forearm and hand.

How is a radial palsy diagnosed?

The story of sudden onset wrist drop is the first clue to a doctor. There is a specific pattern of weakness, reflex, and sensation changes that are easy for a physiatrist, neurologist, or nerve/muscle specialist to spot. More serious problems like stroke is often considered when it first happens and some people attending an emergency room might have tests to rule out a stroke. Often people will have an EMG and Nerve Conduction Study in order to electrically confirm the dysfunction in the radial nerve and determine how severe the injury is.

Will the nerve heal by itself?

Nerve injuries occur to the myelin (insulation around the nerve) and axons (microscopic wires running through the nerves).  In this kind of nerve injury it most often is an injury purely to the myelin (insulation part).  The body is able to repair myelin fairly easily but it takes time. Damage to the axons (microscopic wires) is more serious and difficult for the body to repair.  The good news is that the majority of people with radial nerve palsy have myelin damage and are expected to make a full recovery. The kind of injury (myelin vs. axons) can be determined by the nerve testing (Nerve conduction study and EMG).

How quickly will the nerve recover and when should I go back to the doctor?

The majority of patients will have mostly recovered by three months.  This is the general time frame it takes the body to repair the myelin (though in some cases much faster). This is assuming that there is no further ongoing injury to the nerve.  If the nerve is exposed to repeated pressure trauma then it may not heal or healing might be prolonged.

If the nerve testing determined that there was also a significant amount of damage to the axons then full recovery will take longer. Axons regrow but very slowly at the rate of 1mm per day or 1 inch per month.  For the nerve to regrow axons from the injury site back to the muscles it may take 6 – 9 months or longer. If there is significant axon damage that has resulted in hand and forearm numbness then that sensation recovery will take even longer.

As most people will have recovered by 3 months I suggest that anyone with significant ongoing weakness go back to the doctor for re-evaluation if weakness is still ongoing after three months from the time that nerve pressure injury has stopped.

What can I do while I’m waiting for the nerve to heal?

The most important thing is to understand the mechanism of this nerve injury and prevent further damage. Try to avoid any sustained pressure to the back of the arm(triceps area).  As described above the most common situations where the nerve is injured is when the arm is hanging over the bed, draped over a chair, or has external pressure over the area of the triceps muscle in the back of the arm.

The ability to grip things is greatly affected by wrist movements. When the wrist is in a flexed position (as experienced in wrist drop), the flexion of the fingers (grip) is very weak and ineffective.  One simple way to assist this function while your nerve is healing is to wear a brace.  A wrist brace that keeps the wrist straight or semi extended will allow you to grab and hold onto things more normally.

When parts of our body aren’t moving they tend to get stiff.  In order to avoid this I suggest that you stretch the wrist and fingers several times a day. To do this, keep the elbow fully extended and gently pull the wrist and fingers back and hold for 30 seconds. This doesn’t have to be done frequently.  Even 3 times a day would be adequate.