The radial nerve is a nerve in the human body that supplies the upper limb. It supplies
the medial, lateral, and long heads of the triceps brachii muscle of the arm, as well
as all 12 muscles in the posterior osteofascial compartment of the forearm and the associated
joints and overlying skin. It originates from the brachial plexus, carrying
fibers from the ventral roots of spinal nerves C5, C6, C8 & T1.
The radial nerve and its branches provide motor innervation to the dorsal arm muscles
and the extrinsic extensors of the wrists and hands; it also provides cutaneous sensory
innervation to most of the back of the hand. The ulnar nerve provides cutaneous sensory
innervation to the back of the little finger and adjacent half of the ring finger.
The radial nerve divides into a deep branch, which becomes the posterior interosseous nerve,
and a superficial branch, which goes on to innervate the dorsum of the hand.
Structure The radial nerve originates as a terminal
branch of the posterior cord of the brachial plexus. It goes through the arm, first in
the posterior compartment of the arm, and later in the anterior compartment of the arm,
and continues in the posterior compartment of the forearm.
In arm From the brachial plexus, it travels posteriorly
through what is often called the triangular interval, the lower triangular space of the
axilla or the triceps hiatus.
Having passed through this inter muscular gap, the radial nerve continues posteriorly
in a medial to lateral fashion on the arm while in conjunction with the axillary artery/brachial
artery. The nerve will first give off branches to
the medial head of the triceps brachii and then enter a groove on the humerus, the radial
sulcus, where it innervates the lateral head of the triceps. It is commonly believed that
the radial nerve also provided motor innervation to the long head of the triceps. However,
a study conducted in 2004 determined that, in 20 cadaveric specimens and 15 surgical
dissections on participants, the long head was innervated by a branch of the axillary
nerve in all cases. With the lateral and medial heads of the triceps
innervated, the radial nerve emerges from the radial groove on the lateral aspect of
the humerus. At this point, it pierces the lateral intermuscular
septum and enters the anterior compartment of the arm.
It then courses inferiorly between the brachialis and brachioradialis muscles.
When the radial nerve reaches the distal part of the humerus, it passes anteriorly to the
lateral epicondyle and continues in the forearm. In forearm
In the forearm, it branches into a superficial branch and a deep branch.
The superficial branch of the radial nerve descends in the forearm under the brachioradialis.
It crosses brachioradialis to enter posterior of forearm near the back of the wrist and
supply dorsum of hand. It gives nerve supply to dorsal aspect of thumb, index finger, and
radial side of middle finger except the nail beds, which are supplied by proper digital
branches of median nerve. The deep branch of the radial nerve pierces
the supinator muscle, winds around the radius under the cover of supinator to reach posterior
of forearm where it again pierces supinator and after which it is known as the posterior
interosseous nerve of forearm.It pierces the posterior extensor muscles and comes to lie
on posterior interosseous membrane just below extensor pollices brevis. It continues to
move along with posterior interosseous artery(a deep branch of common interosseous artery
which is a branch of ulnar artery), and ends as a pseudoganglion below extensor retinaculum.
Function The following are branches of the radial nerve.
Cutaneous
Cutaneous innervation by the radial nerve is provided by the following nerve branches:
Posterior cutaneous nerve of arm Inferior lateral cutaneous nerve of arm
Posterior cutaneous nerve of forearm The superficial branch of the radial nerve
provides sensory innervation to much of the back of the hand, including the web of skin
between the thumb and index finger. Motor
Muscular branches of the radial nerve: Triceps brachii
Anconeus Brachioradialis
Extensor carpi radialis longus Deep branch of the radial nerve:
Extensor carpi radialis brevis Supinator
Posterior interosseous nerve: Extensor digitorum
Extensor digiti minimi Extensor carpi ulnaris
Abductor pollicis longus Extensor pollicis brevis
Extensor pollicis longus Extensor indicis
The radial nerve provides motor innervation to the muscles in the posterior compartment
of the arm and forearm, which are mostly extensors. Clinical significance
Injury Injury to the radial nerve at different levels
causes different syndromes with varying motor and sensory deficits.
At the axilla Common mechanisms of injury: Saturday night
palsy, crutch palsy Motor deficit:
Loss of extension of forearm, weakness of supination, and loss of extension of hand
and fingers. Presence of wrist drop, due to inability to
extend the hand and fingers.
Sensory deficit: Loss of sensation in lateral arm, posterior forearm, the radial half of
dorsum of hand, and dorsal aspect of radial 3½ digits, excluding their nail beds.
At mid-arm Common mechanism of injury: Mid-shaft humeral
fracture Motor deficit:
Weakness of supination, and loss of extension of hand and fingers.
Presence of wrist drop, due to inability to extend the hand and fingers.
Sensory deficit: Loss of sensation in posterior forearm, the radial half of dorsum of hand,
and dorsal aspect of radial 3½ digits, excluding their nail beds.
Just below the elbow Common mechanism of injury: Neck of radius
fracture, elbow dislocation or fracture, tight cast, rheumatoid nodules, injections due to
tennis elbow, injuring the deep branch of the radial nerve that pierces the radial head,
causing posterior interosseous nerve syndrome Motor deficit:
Weakness in extension of hand and loss of extension of fingers.
Presence of finger drop, and partial wrist drop, since the extensor carpi radialis longus
and brachioradialis muscles are working.
Sensory deficit: None, as sensation is supplied by the superficial radial nerve
Within the distal forearm: Common mechanism of injury: Wartenberg's syndrome,,
due to nerve entrapment beneath the tendinous insertion of brachioradialis, tight jewellery,
and watch bands. Motor deficit: None
Sensory deficit: Numbness and tingling in radial half of dorsum of hand, and dorsal
aspect of radial 3½ digits, excluding their nail beds.
In Wartenberg's syndrome, there is significant radial wrist pain, and close resemblance to
symptoms in de Quervain's tenosynovitis. Finkelstein's test may be positive.
History Additional images
References
See also This article uses anatomical terminology;
for an overview, see anatomical terminology. Muscular branches of the radial nerve
Posterior brachial cutaneous nerve Dorsal antibrachial cutaneous nerve
Superficial branch of the radial nerve Deep branch of the radial nerve
Radial neuropathy Radial tunnel syndrome
External links Radial_nerve at the Duke University Health
System's Orthopedics program Atlas image: hand_plexus at the University
of Michigan Health System - "Axilla, dissection, anterior view"