The radial nerve is a major peripheral nerve of the upper limb, and in this article, we shall delve into its anatomy, exploring its anatomical course and its motor and sensory functions. We shall also analyze the clinical consequences of any damage to the nerve.
The radial nerve originates in nerve roots C5-T1 and has two distinct functions; sensory and motor. Its sensory function innervates most of the skin of the posterior forearm, the lateral aspect of the dorsum of the hand and the dorsal surface of the lateral three and a half digits. Its motor function, meanwhile, innervates the triceps brachii and the extensor muscles in the forearm.
The radial nerve is the terminal continuation of the posterior cord of the brachial plexus and contains fibres from nerve roots C5-T1. The nerve begins in the axilla region, situated posteriorly to the axillary artery, before exiting the axilla inferiorly via the triangular interval and supplying branches to the long and lateral heads of the triceps brachii.
The nerve then descends down the arm, travelling in a shallow depression within the surface of the humerus known as the radial groove. As it descends, the radial nerve wraps around the humerus laterally, and supplies a branch to the medial head of the triceps brachii, while often being accompanied by the deep branch of the brachial artery.
To enter the forearm, the radial nerve travels anterior to the lateral epicondyle of the humerus through the cubital fossa, before terminating by dividing into two branches. The deep branch - the motor branch - innervates the muscles in the posterior compartment of the forearm, while the superficial branch - the sensory branch - contributes to the cutaneous innervation of the dorsal hand and fingers.
The radial nerve innervates the muscles located in the posterior arm and posterior forearm. In the arm, it innervates the three heads of the triceps brachii, which acts to extend the arm at the elbow joint. The radial nerve additionally gives rise to branches that supply the brachioradialis and extensor carpi radialis longus (muscles of the posterior forearm).
A terminal branch of the radial nerve - the deep branch - innervates the remaining muscles of the posterior forearm. Generally speaking, these muscles act to extend the wrist and finger joints, as well as to supinate the forearm. It is important to note that when the deep branch of the radial nerve penetrates the supinator muscle of the forearm, it is termed the posterior interosseous nerve for the remainder of its course.
There are four branches of the radial nerve that provide cutaneous innervation to the skin of the upper limb. Three of these branches originate in the upper arm - the lower lateral cutaneous nerve of arm, which innervates the lateral aspect of the arm inferior to the insertion of the deltoid muscle, the posterior cutaneous nerve of arm, which innervates the posterior surface of the arm, and the posterior cutaneous nerve of forearm, which innervates a strip of skin down the middle of the posterior forearm.
The fourth branch - the superficial branch - is a terminal division of the radial nerve, supplying innervation to the dorsal surface of the lateral three and half digits as well as the associated area on the dorsum of the hand.
Injury to the radial nerve can be broadly categorized into four groups, depending on where the damage has occurred and which components of the nerve have been affected. In the axilla, the radial nerve can be damaged by a shoulder joint dislocation or a fracture of the proximal humerus, or occasionally by excessive pressure on the nerve within the axilla (e.g. placing the arm in an awkward position for an extended period).
Injury can also occur when the nerve pierces the deep fascia of the arm, when the nerve traverses the cubital fossa and while the nerve passes through the superficial fascia of the forearm. Damage to the radial nerve is usually accompanied by severe pain radiating down the back of the arm into the hand, as well as an inability to extend the wrist joint or fingers, and a wasting of the muscles in the thumb, index finger and middle finger.
Fortunately, radial nerve injuries can often be treated with physical therapy, such as joint mobilisation and muscle stretching. Surgery may be necessary if there is an entrapment of the nerve, and further treatment may be necessary if there is nerve damage, such as tendon transfers and nerve grafting.
The radial nerve is a major nerve of the arm. It originates in the axilla, exiting inferiorly through the triangular interval and supplying branches to the long and lateral heads of the triceps brachii. After travelling down the arm in a shallow depression known as the radial groove, the radial nerve wraps around the humerus laterally and supplies a branch to the medial head of the triceps brachii. During much of its course within the arm, the radial nerve is accompanied by the deep branch of the brachial artery. It eventually enters the forearm and divides into two branches: the deep branch, which is motor, and the superficial branch, which is sensory.
The radial nerve innervates the muscles located in both the posterior arm and the posterior forearm. In the arm, it innervates the three heads of the triceps brachii, which acts to extend the arm at the elbow. In addition, the radial nerve gives rise to branches that supply the brachioradialis and extensor carpi radialis longus muscles. These muscles generally act to extend the wrist and finger joints, as well as supinate the forearm. Once the deep branch of the radial nerve penetrates the supinator muscle of the forearm, it is referred to as the posterior interosseous nerve for the remainder of its course.
The radial nerve provides cutaneous innervation to the skin of the upper limb via four branches. Three of these branches arise in the upper arm, including the lower lateral cutaneous nerve of arm, the posterior cutaneous nerve of arm, and the posterior cutaneous nerve of forearm. The fourth branch, the superficial branch, is a terminal division of the radial nerve and innervates the dorsal surface of the lateral three and a half digits and the associated area on the dorsum of the hand.
Injuries to the radial nerve can generally be classified into four groups based on the location of the damage and affected components of the nerve. When the radial nerve is injured in the axilla, motor functions of the triceps brachii and muscles in the posterior compartment are affected. The patient is unable to extend at the forearm, wrist, and fingers, and this is known as wrist-drop. Additionally, all four cutaneous branches of the radial nerve are affected, resulting in a loss of sensation over the lateral and posterior arm, posterior forearm, and dorsal surface of the lateral three and a half digits.
Injury to the radial nerve in the radial groove is common with a fracture of the humeral shaft. The triceps brachii may be weakened, but is not paralysed. Similarly, the muscles of the posterior forearm are affected, resulting in the patient's inability to extend at the wrist and fingers. Again, the superficial branch of the radial nerve will be damaged, resulting in sensory loss to the dorsal surface of the lateral three and a half digits and the associated area on the dorsum of the hand.
Finally, when the radial nerve is injured in the forearm, the typical mechanism of injury and its effect on the nerve differ, depending on which branch is affected. If the superficial branch is injured, stabbing or laceration of the forearm may result. However, if the deep branch is affected, a fracture of the radial head or a posterior dislocation of the radius is likely. Injuries to the superficial branch cause no motor deficits, whereas the deep branch can affect the majority of the muscles in the posterior forearm, resulting in an inability to extend at the wrist and fingers.
The radial nerve is a large nerve that originates in the brachial plexus and supplies the triceps as well as the skin of the posterior of the arm and forearm. It passes through the axilla and enters the radial groove of the humerus before winding around the humerus and continuing down the posterior of the arm, along the back of the elbow. In the lower arm, it follows the lateral side of the radius and divides into its motor and sensory branches.
Prosection imaging is often used to better understand the course of the radial nerve, as well as the exact motor and sensory components. Together, these components provide motor output to the elbow and wrist joint, enabling flexion and extension of the wrist and the fingers, and provide sensory input from the skin of the posterior of the arm and forearm.
Injuries to the radial nerve can result in paralysis of the triceps and cause disturbances to the sensory input of the proximal forearm. One common clinical presentation of nerve injury is wrist-drop, caused by damage to an associated muscle of the radial nerve, the extensor carpi radialis longus. Wrist-drop occurs when this muscle is unable to cause extension at the wrist joint, resulting in the inability to flex the fingers. Sensory loss from the radial nerve typically affects the lateral 3 ½ digits, and the associated area on the dorsum of the hand.
Damage to the deep branch of the radial nerve is a more severe injury, leading to complete numbness and paralysis of the triceps and the anconeus muscles. In serious cases, deep branch nerve injury can even lead to elbow flexion contracture, leading to the inability to fully extend the elbow joint.
By understanding the anatomy and clinical presentation of injuries to the radial nerve, healthcare providers can better diagnose and treat any injuries that may occur.
