RADIAL NERVE: ANATOMY AND FUNCTIONS - ANATOMY AND PHYSIOLOGY - 2025

The radial nerve is a peripheral nerve existing in the human body that innervates the posterior part of the upper extremities. It originates in the posterior cord of the brachial plexus and receives contributions from the roots of the spinal nerves C5, C6, C7, C8, and T1.

The radial nerve provides both a motor and sensory function to the arm and forearm, as well as sensory innervation of the hand. It originates from the posterior cord of the brachial plexus, behind the axillary artery, and is in the armpit and reaches the posterior compartment of the arm passing under the teres major muscle.

In this compartment it snakes around the spiral groove of the humerus, accompanied by the deep brachial artery. It then penetrates the lateral intermuscular septum until it reaches the anterior compartment of the arm.

It then goes through the elbow to reach the forearm. There, it enters the ulnar fossa, dividing into superficial and deep branches.

- Deep branch: it has motor functions and innervates most of the muscles of the posterior compartment of the forearm. The posterior interosseous nerve starts from this branch, which passes between the supinator muscle, enters the posterior compartment of the forearm and ends at the wrist joint.

- Superficial branch: it is in charge of sensory innervation, mainly of the skin, the hand and the fingers. This branch of the radial nerve travels toward the wrist lateral to the radial artery and enters the hand. In it they are divided into digital cutaneous branches.

Radial nerve functions

The radial nerve constitutes the nerve endings of muscles of the arm, forearm, wrist, and hand, as well as providing sensitivity to the back of the hand. Most muscles that the radial nerve activates are extensors.

Motor functions

The radial nerve provides movement to the muscles located in the back of the upper arm, as well as in the posterior forearm.

In the upper arm, the radial nerve innervates the three heads of the triceps brachii, which helps to extend the arm at the elbow.

This nerve is also responsible for muscles of the posterior forearm such as the brachioradialis and extensor carpi radialis longus.

The deep branch of the radial nerve, which is a terminal branch, supplies the rest of the muscles of the posterior forearm. These muscles generally serve to extend the wrist and finger joints. They also allow supination of the forearm.

Sensory functions

There are four branches of the radial nerve that provide cutaneous innervation to the skin of the upper extremities. Three of them originate from the upper arm. These branches are:

- Lower arm lateral cutaneous nerve: this gives sensitivity to the lateral aspect of the upper arm, below the deltoid muscle.

- Posterior cutaneous nerve of the arm: activates the posterior surface of the upper arm.

- Posterior cutaneous nerve of the forearm: innervates an area of ​​skin that runs through the middle of the forearm, from the elbow to the wrist.

- Superficial branch: it is the terminal division of the radial nerve. It activates the surface of the back of the hand, as well as the thumb, index, middle and middle of the ring finger.

Radial nerve pathologies

Pathologies in the radial nerve can be complex and can occur anywhere (axillary level, in the radial tunnel, in the posterior interosseous, in the superficial branch, etc.).

- Radial tunnel

One of the most common pathologies is radial tunnel syndrome. It involves compression of the posterior interosseous nerve in the forearm, in the posterior area of ​​the arm or the elbow. Its main causes are trauma, tumors, lipomas (fatty tissue tumors), gaglions (cysts), inflammation, etc.

The main symptoms are: stabbing pain in the upper part of the forearm, on the back of the hand and on one side of the elbow. This pain is accentuated when the patient stretches the wrist and fingers of the hand.

Unlike what occurs in other pathologies of the nerves, it does not cause numbness because the radial nerve innervates mainly muscles.

Treatment consists of a splint on the wrist and / or elbow. Although if this does not solve the problem, surgery may be necessary.

- Radial neuropathy

If the radial nerve is injured it can result in radial neuropathy, also known as radial nerve palsy. This can be due to many causes such as a broken humerus, sleeping in an uncomfortable position, infections, and even exposure to toxins.

It manifests as tingling, numbness, weakness, or trouble moving the wrist, hand, or fingers. It may or may not be accompanied by pain. This injury is treated by intervening in its underlying causes.

- Classification according to location

Radial nerve injury can be classified into three groups according to the location of the damage, since the symptoms will be different.

At the armpit level

The radial nerve can be injured in this area by a shoulder dislocation, or a proximal humerus fracture. Symptoms are motor deficits in the triceps brachii and posterior compartment muscles.

In this way, the patient cannot extend the forearm, wrist, or fingers. It is common to observe unopposed wrist flexion. In addition, the four cutaneous branches of the radial nerve are also altered.

There is a loss of sensation in the upper lateral and posterior arm, the posterior forearm and the back of the first three fingers.

Radial groove

The radial nerve is susceptible to injury if there is a fracture of the shaft of the humerus. It is manifested by weakness (but not paralysis) of the triceps brachii, problems to extend the wrist and fingers due to alterations in the posterior forearm.

On the forearm

As there are two terminal branches in the forearm, the symptoms will vary according to the affected branch. Thus, a lesion that covers the superficial branch produces a sensory loss of the innervated fingers and their associated palm, with preservation of motor functions.

Damage to the deep branch affects the motor functions of the forearm muscles, with no sensory loss.

It is also observed in the loss of sensation of the dorsal part of the first three fingers and half of the ring finger, as well as its associated palm.

For symptoms, anti-inflammatory drugs, pain relievers, anticonvulsants, or tricyclic antidepressants may be prescribed. Orthotics or splints may be recommended, as well as physical therapy.

References

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4. Steinberg, D. (nd). Radial tunnel syndrome. Retrieved on April 16, 2017, from MSD Manual: msdmanuals.com.
5. THE RADIAL NERVE. (sf). Retrieved on April 16, 2017, from Teach me anatomy: teachmeanatomy.info.