Radial Nerve Injury - Symptoms and Treatment

Another Cause of Hand Weakness and Numbness

A depiction of the radial nerve. Gray's Anatomy

Imagine that you are positioning your hands to push hard against something. The wrists are bent back, and the arms begin to straighten. All of these actions depend on the radial nerve, which controls most of the actions required to push something away from you.

The radial nerve travels from the neck along the arm to the finger tips. Along the way, it communicates with different muscles and regions of skin to signal for muscles to contract and send sensory signals back to the brain.

The nerve is prone to injury at certain spots along the way, which leads to distinct patterns of disability and loss.

Injury at the Axilla

Immediately after leaving the brachial plexus, the radial nerve travels under the arm close to the axilla (the armpit). Improper use of crutches is a common cause of nerve compression at this spot, which can lead to impaired radial nerve function throughout the arm.

The radial nerve straightens the arm by causing the triceps muscle at the back of the arm to contract. If the nerve is injured before it supplies the triceps, the arm will be weak when pushing something away. It may also be impossible to bend the wrist back, resulting in a "wrist drop." Finger extensors will also be weak, making it challenging to fully open the hand.

The radial nerve also innervates the brachioradialis muscle, which, unlike other muscles innervated by the radial nerve, bends the arm at the elbow, but only when the fist is held in a position as if it were about to bang on a table.

A doctor concerned about radial nerve injury may test the strength of this muscle as well.

In addition to weakness, people with radial nerve injuries may suffer numbness in the area where the nerve runs along the back of the arm. This numbness may extend all the way down to the hand, especially the side and back of the thumb.

Injury at the Spiral Groove

Like all the other nerves in the arm, the radial nerve is made of a collection of fibers from the brachial plexus, an intertwining of nerve roots exiting the spinal cord. After leaving the brachial plexus, the radial nerve goes down the arm. Along the way, it wraps around the humerus, the arm bone between the shoulder and elbow, in a channel called the spiral groove. The nerve travels along the back of the arm from there on.

The nerve can be compressed within the spiral groove, leading to weakness of the muscles that bend the wrist back and straighten the fingers. A dramatic example can occur with humerus fractures, in which case the nerve can be injured or cut by shards of bone. Another less traumatic example is the "Saturday night palsy," so called because inebriated people who fall asleep with their arm draped over the back of a park bench may not wake when the nerve signals its discomfort, and may wake in the morning with nerve damage.

The parts of the radial nerve that stimulate the triceps branch off before the spiral groove, and so the triceps may retain full strength in this injury.

The brachioradialis will likely still be weakened, though.

Close testing of radial nerve injuries is required because this type of injury can mimic more serious disorders of the central nervous system (the brain and spinal cord) such as stroke. These injuries also often cause more weakness of muscle extension than flexion. The sparing of the triceps, sensory loss along the back of the arm, and especially brachioradialis weakness can help distinguish radial nerve injury at the spiral groove from problems of the brain or spinal cord.

Posterior Interosseous Syndrome

Just before entering the elbow, the radial nerve then sends off a major branch, the posterior interosseous nerve. Unlike other branches of the radian, this nerve does not have any sensory components, and so this results in pure muscle weakness.

The posterior interosseous nerve is responsible for straightening almost anything below the elbow. Finger extension will be weak. There is one exception, though. A major muscle that extends the wrist, the extensor carpi radialis, is actually innervated before the branching of the posterior interosseous, and so the wrist drop may not be as obvious in posterior interosseous syndrome as in the injuries already mentioned. When the wrist is extended, however, the hand may be pulled in one direction more than another, since another muscle that pulls on the wrist from the other side, the extensor carpi ulnars, is innervated by the posterior interosseous, and will be too weak to match the fully intact action of the extensor carpi radialis. The brachioradialis and the triceps will both be spared.

Although posterior interosseous neuropathy does not cause sensory loss, the disorder can still be very painful, as it is often caused by inflammation of tissue where the nerve passes between the two bones of the forearm (the radialis and ulna) or in severe lateral epicondylitis (tennis elbow). The pain is generally worse with finger extension, as this uses and aggravates the inflamed tendons.

Superficial Radial Neuropathy

After the branching off of the posterior interosseous, the radial nerve continuous down to the back of the hand as the superficial branch of the radial nerve, where it has a purely sensory function. The nerve here is most susceptible to injury at the wrist, as can be the case in handcuffs that are worn too tightly.

The pattern of numbness is usually worst from the wrist to the back of the thumb, and may feel like the sensation of having lidocaine injected for a dental procedure. A painful electrical feeling may also shoot up or down the back of the hand. A "pins and needles" feeling may also be present.

Prognosis and Treatment

If nerve injury is due to compression at one of the sites described above, it is usually best to focus on preventing further injury so that the nerve can heal on its own. Splinting the wrist may be needed to allow the use of the hand. Pain management can be done with medications such as anti-inflammatories. In extreme cases, a nerve block may be used to prevent pain, though this may further reduce desired nerve function as well.

In mild cases such as this, full recovery is expected, though it can take time for the nerve to heal. In one study, the time to full recovery ranged from a couple of weeks to 6 months, with an average time of three and a half months.

People whose radial nerve has been injured by severe trauma, with no sign of improvement, may warrant further investigation with studies such as nerve conduction studies or electromyography. Surgical options may then be considered. Surgery may also be an option for severe nerve entrapments, such as posterior interosseous syndrome, that do not improve with time.


Arnold WD, Krishna VR, Freimer M, et al. Prognosis of acute compressive radial neuropathy. Muscle Nerve 2012; 45:893.

Barnum M, Mastey RD, Weiss AP, Akelman E. Radial tunnel syndrome. Hand Clin 1996; 12:679.

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