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Radial nerve

Also called posterior interosseous nerve, superficial radial nerve

The nerve that winds round the back of the upper arm to the back of the forearm and hand. Where it runs, what it supplies, where it gets pressed on, and what studies report about recovery.

Region
Forearm
Updated
October 14, 2026
Reviewed
October 14, 2026 · how entries are checked

Function

Where it starts and what it does

The radial nerve arises from the spinal nerves labelled C5 to T11. It belongs to the brachial plexus, the network of nerves, starting at the neck, that serves the arm1. It leaves from the network’s posterior cord, one of its large nerve bundles, along with the axillary nerve7,8.

The nerve carries both movement and feeling1. Its motor branches, which carry signals to muscles, drive the muscles of the back of the arm and forearm1. Those include the forearm muscles that straighten the wrist and fingers1.

Its path down the upper arm

A review describes the nerve leaving the armpit behind the brachial artery, the main artery of the upper arm6. It passes between two heads of the triceps brachii, the three-headed muscle on the back of the upper arm6. It then runs in the radial groove, a shallow channel that winds around the back of the upper arm bone6. That bone is the humerus, and the groove lies on the middle third of it9.

Engraving of the right shoulder blade and arm from behind with three nerves drawn in yellow. The axillary nerve comes out below the teres minor muscle, beside the long head of the triceps, and branches into the underside of the deltoid, which is cut and turned up. The suprascapular nerve crosses the top of the shoulder blade to the supraspinatus and infraspinatus. The radial nerve winds down the back of the upper arm between the heads of the triceps and its deep branch continues into the back of the forearm.
Axillary nerve at the back of the shoulder, with the suprascapular and radial nervesHenry Vandyke Carter, in Henry Gray, Anatomy of the Human Body (1918), Fig. 818. Public domain, via Wikimedia Commons. (source, Public domain)

In the upper third of the arm, triceps muscle lies between the nerve and the bone, one review states10. In the lower third the nerve lies straight on the bone’s covering, with no muscle between10. The nerve pierces the lateral intermuscular septum, a sheet of tough tissue that separates groups of muscles6,10. It then runs between the brachialis and the brachioradialis, two muscles that bend the elbow6,10.

Its two branches below the elbow

The nerve divides into a superficial (shallow) branch and a deep branch11. In 20 limbs from cadavers (bodies donated for study), the split lay within 2.1 cm of the outer elbow bump in every limb12.

  • The deep branch normally passes between the heads of the supinator into the back of the forearm11. The supinator is a muscle that helps turn the hand palm-up13. The branch comes out as the posterior interosseous nerve, which supplies the muscles there11. On its way it passes through the radial tunnel6,14. A review defines that tunnel as the space from the elbow joint down to the lower edge of the supinator’s shallow layer6.
  • The superficial branch is described as purely sensory in one source and mainly sensory in another6,15. It comes out from under the brachioradialis to lie beneath the skin of the back of the forearm6. At the wrist it splits into branches to the back of the thumb, index finger and half the middle finger6.
Engraving of the outline of a right arm and hand seen from behind, with the nerves that run under the skin drawn in yellow. On the back of the upper arm a branch is labelled posterior brachial cutaneous, and down the back of the forearm one is labelled dorsal antibrachial cutaneous. At the thumb side of the wrist a nerve labelled radial comes to the surface and fans out over the back of the hand to the thumb, index and middle fingers. The ulnar nerve is labelled on the little-finger side of the hand, and the axillary and other skin nerves are labelled higher up.
Skin nerves of the back of the arm, forearm and hand, with the radial nerve's branchesHenry Vandyke Carter, in Henry Gray, Anatomy of the Human Body (1918), Fig. 813. Public domain, via Wikimedia Commons. (source, Public domain)

The nerve’s sensory branches supply skin on the back of the forearm, and on the back and thumb side of the wrist and hand1. On the hand its share of skin shrinks from the thumb towards the ring finger1. The finger pads belong to the median nerve and the ulnar nerve1.

How it slides as the arm moves

One study measured how far the nerve had to slide in ten arms from five cadavers16.

Slide needed (mm)Wrist, tilted 15 degrees to the thumb side, then 30 to the other4.3 Elbow, from 10 to 90 degrees8.8 Wrist, fingers, elbow and shoulder movements combined9.4 Wrist, fingers, elbow and shoulder movements combined14.2
Slide needed (mm). Bars start at zero; the table below gives each value with its source.
Movement, in the same ten cadaver armsWhere the slide was measuredSlide needed (mm)
Wrist, tilted 15 degrees to the thumb side, then 30 to the otherWrist4.316
Elbow, from 10 to 90 degreesElbow8.816
Wrist, fingers, elbow and shoulder movements combinedWrist9.416
Wrist, fingers, elbow and shoulder movements combinedElbow14.216

Over that elbow movement, the same study measured 28% strain, or stretch as a share of length, in the nerve at the elbow16.

Where it crosses the septum

Two cadaver studies looked at the nerve near the lateral intermuscular septum17,18. In eight paired arms, it slid less in the upper arm than the median and ulnar nerves did17. Bending the elbow to 90 degrees doubled its slide, and cutting the septum as well tripled it17. In 27 specimens, the nerve had very little mobility where it entered the front of the arm, between the septum and the bone18. A review states that the nerve’s movement is greatly restricted where it pierces that septum10.

Measurements in living people

In healthy people, ultrasound (a scan made with sound waves) showed the nerve sliding 0.41 to 4.03 mm as the wrist bent forward19. A 2014 review of sliding measured in living people included 12 studies, and none was on the radial nerve20.

A 2017 review of limb movement and nerve stretch in living people covered 22 studies, 15 on the median nerve21. The rest were on the sciatic (four), tibial (two), ulnar (one) and peroneal (one) nerves21. Its authors state that nerve behaviour under stretch is not well established in living people21. The studies differed too much in nerves, sites and joint positions to pool21.

Breakdown

Pressure in the upper arm

In 20 years of US emergency department records, sleeping position was the main mechanism of radial nerve injury, at 62%2.

A review defines “Saturday night palsy” as direct pressure on the nerve in the arm from a firm object, usually at the radial groove6.

Wrist drop is the loss of wrist straightening after radial nerve injury6. In a study of 25 patients with posture-related wrist drop, 68% of cases followed sleeping after getting drunk22. Most of the 25 (88%) had been pressed on for 2 to 4 hours22. A review states that injury in the arm does not much affect the triceps, so the elbow can still be straightened10.

Hard muscular effort

A review names three places in the arm where the nerve is prone to being squeezed10:

  • between the heads of the triceps10;
  • in the groove of the humerus10;
  • where it pierces the lateral intermuscular septum10.

A systematic review is a study that searches for all the research on a question in a checkable way. One such review of squeezing in the upper arm without injury found only 12 studies, with 21 patients23. In 16 cases the mechanism was sudden or repeated elbow straightening with forceful muscle contraction23.

The sport evidence cited here is three reports, each on one or two people24,25,26:

  • an elite bodybuilder, whose palsy was put down to the bulk of enlarged muscle pressing on the nerve24;
  • a 21-year-old collegiate baseball pitcher, with outer arm pain and weak wrist straightening after pitching25;
  • two competitive softball players, whose severe nerve injuries were attributed to the “windmill” pitching motion26.

A broken upper arm

One systematic review found radial nerve palsy in 11.8% of humeral shaft fractures (breaks of the upper arm bone’s shaft), 532 of 4,5173. An updated review, covering studies from 1964 to 2017, put the figure at 12.3%27.

The deep branch in the forearm

The arcade of Frohse is the tendon-like upper edge of the supinator’s shallow layer, and the deep branch passes beneath it28. A meta-analysis is a study that pools the results of several earlier studies. One meta-analysis reports that the arcade is considered the most common place for that branch to be squeezed28. Pooling 20 anatomical studies, it found the arcade in 66% of adults28.

Two patterns are described, and sources disagree about one of them6,29:

  • Posterior interosseous nerve syndrome often shows as weakness straightening the fingers and thumb, with wrist straightening kept11. Skin feeling stays normal6.
  • Radial tunnel syndrome is described in one review as pain and tenderness along the same nerve, with no muscle weakness or loss of feeling6. A 1999 review argues it is debatable whether squeezing of the radial nerve causes that pain29.

One study compared 21 industrial workers who had radial tunnel syndrome with 21 matched workers who did not30. Odds were higher for those who worked with the elbow fully straight, and no link was found with sport or leisure activities30. A review of sports nerve injuries lists posterior interosseous nerve syndrome in sports with repeated forearm turning and wrist straightening31.

The superficial branch at the wrist

A review defines Wartenberg syndrome as a squeezing problem affecting only the superficial branch6. The branch is thought to be open to outside pressure at the wrist because it runs just under the skin close to the bone6.

The first dorsal compartment of the wrist holds two tendons32,33. In 20 cadaver arms, the nearest branch of the superficial radial nerve lay a mean of 0.4 cm from the centre of that compartment12. De Quervain’s disease is painful swelling around two thumb tendons at the wrist. It was present in half of a series of 52 cases of squeezing of the superficial branch34. A review states that Wartenberg syndrome is sometimes confused with De Quervain’s6.

Recovery

What the grade of injury means

A review of nerve tissue states that most nerve compressions are the mildest grade of injury, neurapraxia35. Another describes neurapraxia as a temporary signal block that clears fully within 12 weeks36. Where the fibres themselves are damaged, regrowth is slow, about 1 mm a day, and often incomplete36.

After pressure or effort in the arm

Group studiedWhat was reported
Pressure palsies of the nerve in the arm, in a reviewTypically complete in 2 or 3 months; up to 6 in more severe cases6
25 patients with wrist drop after holding one posture for a long timeA mean of 2.4 weeks passed before improvement began22
51 patients with a radial nerve problem from pressure, confirmed by nerve testingAll 23 with follow-up recovered completely, a mean of 3.4 months after onset4
21 published patients with squeezing in the upper arm without injuryAll four not operated on recovered completely; of 18 operated on, 12 recovered completely, one partly and four not at all23

After a broken upper arm

One systematic review found that 88.1% of nerves recovered overall after palsy with a humeral shaft fracture3. In patients not operated on, 70.7% recovered on their own3. An updated review found recovery on its own in 77.2% of patients not operated on27. It found recovery in 89.8% of those who had surgery to explore the nerve and repair the fracture within 3 weeks27.

In the forearm and at the wrist

A 2008 systematic review found no randomised or controlled trials (studies that compare groups) of any approach to radial tunnel syndrome5. The authors of a 2024 systematic review conclude that outcomes are hard to compare across studies37.

In the series of 52 superficial branch cases, 71% of those not operated on had excellent or good results34. So did 74% of those operated on34.

Connections

The muscles it supplies

The triceps is mainly supplied by the radial nerve38. Branches straight from the main trunk supply, in order, the triceps, anconeus, brachioradialis and extensor carpi radialis longus6. The anconeus is a small muscle at the back of the elbow, and the last is a forearm muscle that pulls the wrist back. In Gray’s account, most other muscles of the back of the forearm, the forearm extensors, are supplied through the deep branch13.

A review gives the order in which the posterior interosseous nerve reaches them6:

  • first the supinator and the extensor carpi radialis brevis6;
  • then, through one branch past the supinator, the extensor carpi ulnaris and the long and short thumb extensors6;
  • through the other, the extensor digitorum, extensor digiti minimi, extensor indicis and abductor pollicis longus6.

Exercises and stretches that load it

In five cadaver elbows, pressure in the radial tunnel rose when the wrist moved from neutral to a bent-forward, palm-down position39. Related exercise pages: wrist extensor stretch, wrist extension, triceps extension1,38,39.

Radial nerve supplies

Radial nerve runs in a groove on the back of

Radial nerve leaves the brachial plexus alongside

Radial nerve shares the skin of the hand with

Radial nerve sends branches to

Radial nerve has skin branches lying beside

Radial nerve has a branch whose squeezing is sometimes confused with

Radial nerve has a forearm pain syndrome that is compared with pain at

Radial nerve is loaded by

Radial nerve supplies the muscles worked in

Radial nerve supplies the muscle worked in

Sources

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  2. Boroumand S, Ajjawi I, Gu E, Littleton A, Flores-Pérez P, Vafa AZ, Klimitz FJ, Diatta F (2026). Exploring 20 years of peripheral nerve injuries of the upper extremity: An analysis of median, radial, and ulnar nerve injuries presenting to US emergency departments.. Journal of Hand Therapy. doi:10.1016/j.jht.2026.02.012 PMID 41966926
  3. Shao YC, Harwood P, Grotz MR, Limb D, Giannoudis PV (2005). Radial nerve palsy associated with fractures of the shaft of the humerus: a systematic review.. Journal of Bone and Joint Surgery. British Volume. doi:10.1302/0301-620X.87B12.16132 PMID 16326879
  4. Arnold WD, Krishna VR, Freimer M, Kissel JT, Elsheikh B (2012). Prognosis of acute compressive radial neuropathy.. Muscle & nerve. doi:10.1002/mus.23305 PMID 22581545
  5. Huisstede B, Miedema HS, van Opstal T, de Ronde MT, Verhaar JA, Koes BW (2008). Interventions for treating the radial tunnel syndrome: a systematic review of observational studies.. The Journal of hand surgery. doi:10.1016/j.jhsa.2007.10.001 PMID 18261668
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  7. Stokey PJ, Kaur S, Lee A, Behrens K, Ebraheim N (2024). Anatomy and Deficiency of the Deltoid Muscle: A Review of Literature.. Orthopedic Reviews. doi:10.52965/001c.115352 PMID 38562147
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  11. Wheeler R, DeCastro A (2023). Posterior Interosseous Nerve Syndrome.. StatPearls. PMID 31082090
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  17. Chen WA, Luo TD, Wigton MD, Li Z (2018). Anatomical Factors Contributing to Radial Nerve Excursion at the Brachium: A Cadaveric Study.. The Journal of hand surgery. doi:10.1016/j.jhsa.2017.09.023 PMID 29122426
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  39. Erak S, Day R, Wang A (2004). The role of supinator in the pathogenesis of chronic lateral elbow pain: a biomechanical study.. Journal of hand surgery (Edinburgh, Scotland). doi:10.1016/j.jhsb.2004.06.001 PMID 15336750

Every source the library cites

Changes

  • First published.