Radial nerve

Radial nerve
The suprascapular, axillary, and radial nerves.
Details
Fromposterior cord
Toposterior interosseous nerve
Innervatesposterior compartment of the arm, posterior compartment of the forearm
Identifiers
Latinnervus radialis
MeSHD011826
TA98A14.2.03.049
TA26431
FMA37069
Anatomical terms of neuroanatomy

The radial nerve is a nerve in the human body that supplies the posterior portion of the upper limb. It innervates the medial and lateral 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, C7, C8 & T1.[1]

The radial nerve and its branches provide motor innervation to the dorsal arm muscles (the triceps brachii and the anconeus) and the extrinsic extensors of the wrists and hands; it also provides cutaneous sensory innervation to most of the back of the hand, except for the back of the little finger and adjacent half of the ring finger (which are innervated by the ulnar nerve).

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 (back) of the hand.

Structure

Radial nerve of the right axilla, posterior view

The radial nerve originates as a terminal branch of the posterior cord of the brachial plexus.[1] 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.

Arm

The radial nerve originates from the posterior cord of the brachial plexus with root values of C5 to C8 and T1. From the brachial plexus, it travels behind the third part of the axillary artery (part of the axillary artery distal to the pectoralis minor). In the arm, it runs behind the brachial artery and then enters the lower triangular space to reach the radial sulcus of back of the humerus.[1] It travel downwards together with profunda brachii artery, between the lateral and medial heads of triceps brachii until it reaches the lateral side the arm at 5 cm below the deltoid tuberosity where it pierces the lateral intermuscular septum to reach the anterior compartment of the arm. Then, it descends down to cross the lateral epicondyle of the humerus where the nerve terminates by branching itself into superficial and deep branch which continues into cubital fossa and then into the forearm.[2]

Radial nerve gives out muscular branches to supply the long head, medial head, and lateral head of triceps brachii muscles before and during its course in the radial sulcus. After it emerges out from the radial sulcus, it supplies the brachialis, brachioradialis and extensor carpi radialis longus.[2]

Above the radial sulcus, the radial nerve gives off posterior cutaneous nerve of the arm which supplies the skin at the back of the arm. In the radial sulcus, it gives off lower lateral cutaneous nerve of the arm and posterior cutaneous nerve of the forearm. The radial nerve also gives articular branches to supply the elbow joint.[2]

Forearm and hand

In the forearm, it is divided into a superficial branch (primarily sensory) and a deep branch (primarily motor).

Variation

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 found out that axillary nerve innervates the long head of triceps in 20 cadavers without any supply from radial nerve.[5]

Function

The following are branches of the radial nerve (including the superficial branch of the radial nerve and the deep branch of the radial nerve/posterior interosseous nerve).

Cutaneous

Cutaneous innervation of the right upper extremity. Areas innervated by the radial nerve are colored in pink.

Cutaneous innervation by the radial nerve is provided by the following nerve branches:

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

Muscles of the posterior forearm. All the labelled muscles (that is, all the visible muscles except the ones on the dorsal hand and one at top left) are innervated by the radial nerve, and represent all muscles innervated by the radial nerve except for the supinator.

Muscular branches of the radial nerve:

Deep branch of the radial nerve:

Posterior interosseous nerve (a continuation of the deep branch after the supinator):

The radial nerve (and its deep branch) 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,[1] crutch palsy, lesions[6]
  • 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.[7][8]
  • Sensory deficit: Loss of sensation[7] in lateral arm, posterior forearm, the radial half of dorsum of hand, and dorsal aspect of radial 3+1⁄2 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.[7][8]
  • Sensory deficit: Loss of sensation in posterior forearm, the radial half of dorsum of hand, and dorsal aspect of radial 3+1⁄2 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:
  • Sensory deficit: None, as sensation is supplied by the superficial radial nerve
    Radial nerve

Within the distal forearm:

History

Additional images

See also

References

  1. 1 2 3 4 Scott, Kevin R.; Ahmed, Aiesha; Scott, Linda; Kothari, Milind J. (2013-01-01), Barnes, Michael P.; Good, David C. (eds.), "Chapter 42 - Rehabilitation of brachial plexus and peripheral nerve disorders", Handbook of Clinical Neurology, Neurological Rehabilitation, Elsevier, 110: 499–514, doi:10.1016/b978-0-444-52901-5.00042-3, ISBN 9780444529015, PMID 23312667, retrieved 2020-10-25
  2. 1 2 3 4 5 Krishna, Garg (2010). "8 - Arm". BD Chaurasia's Human Anatomy (Regional and Applied Dissection and Clinical) Volume 1 - Upper limb and thorax (5th ed.). India: CBS Publishers and Distributors Pvt Ltd. pp. 95, 111, 122, 128. ISBN 978-81-239-1863-1.
  3. ↑ "Acland's video Atlas of Human Anatomy 1.3.1.8 - Radial nerve in the forearm and hand". Wolters Kluwer. Archived from the original on 29 November 2017. Retrieved 26 January 2018. The deep branch of the radial nerve, also known as the posterior interosseous nerve, is a motor nerve.
  4. ↑ Nurul Huda, Mohd Nor; San, Aye Aye; Fauziah, Othman (2014). "An Anomalous Pattern of Superficial Branch of Radial Nerve: A Cadaveric Case Report". International Journal of Morphology. 32 (1): 29–31. doi:10.4067/S0717-95022014000100005. ISSN 0717-9502. The deep branch of radial nerve and also known as posterior interosseous nerve is the nerve of extensor compartment of the forearm ...
  5. ↑ de Sèze MP, Rezzouk J, de Sèze M, Uzel M, Lavignolle B, Midy D, Durandeau A (2004). "Does the motor branch of the long head of the triceps brachii arise from the radial nerve? An anatomic and electromyographic study". Surg Radiol Anat. 26 (6): 459–61. doi:10.1007/s00276-004-0253-z. PMID 15365769. S2CID 10052988.
  6. ↑ Ryan, Monique M.; Jones, H. Royden (2015-01-01), Darras, Basil T.; Jones, H. Royden; Ryan, Monique M.; De Vivo, Darryl C. (eds.), "Chapter 14 – Mononeuropathies", Neuromuscular Disorders of Infancy, Childhood, and Adolescence (Second Edition), San Diego: Academic Press, pp. 243–273, doi:10.1016/b978-0-12-417044-5.00014-7, ISBN 978-0-12-417044-5, retrieved 2020-10-25
  7. 1 2 3 Prakash, M. V. S. Satya; Udupi Bidkar, Prasanna (2016-01-01), Prabhakar, Hemanshu (ed.), "Chapter 37 - Peripheral Nerve Injuries", Complications in Neuroanesthesia, San Diego: Academic Press, pp. 359–368, doi:10.1016/b978-0-12-804075-1.00037-7, ISBN 978-0-12-804075-1, retrieved 2020-10-25
  8. 1 2 Kretschmer, Thomas; Heinen, Christian (2015-01-01), Tubbs, R. Shane; Rizk, Elias; Shoja, Mohammadali M.; Loukas, Marios (eds.), "Chapter 36 - Iatrogenic Injuries of the Nerves", Nerves and Nerve Injuries, San Diego: Academic Press, pp. 557–585, doi:10.1016/b978-0-12-802653-3.00085-3, ISBN 978-0-12-802653-3, retrieved 2020-10-25
  9. ↑ Tor Wo Chiu (2011). Stone's Plastic Surgery Facts and Figures. Cambridge University Press. ISBN 9781139499781.
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