The radial nerve runs the length of the arm, powering the muscles that straighten the wrist and fingers and carrying sensation to the back of the hand. When it’s compressed or trapped — radial nerve entrapment — it can cause anything from weakness and “wrist drop” to nagging outer forearm pain. So where does the radial nerve get trapped, and how do we treat it? 

What does the radial nerve do?

Nerve supply of the hand, including the ulnar nerve distribution

The radial nerve travels down the back of the upper arm, wraps around the humerus, crosses the elbow, and then divides into two branches in the forearm:

  • The posterior interosseous nerve (PIN) — a motor branch that supplies the muscles straightening the wrist and fingers
  • The superficial radial nerve — a sensory branch supplying the back of the hand

Because of this, the symptoms of radial nerve entrapment depend heavily on where along its course the nerve is compressed.

Where does the radial nerve get trapped?

There are several recognised sites:

High compression (upper arm) — “wrist drop”

Where the nerve is compressed against the humerus in the upper arm — for example after a humerus fracture, or from prolonged pressure (the classic “Saturday night palsy”, where the arm is draped over a chair while asleep) — the result is weakness of wrist and finger extension: a wrist drop, often with numbness on the back of the hand.

Radial tunnel (below the elbow) — pain

Where the posterior interosseous nerve is compressed in the radial tunnel just below the elbow, the result is pain over the outer forearm — radial tunnel syndrome — without weakness. This is easily mistaken for tennis elbow.

Posterior interosseous nerve syndrome — weakness

Where the same PIN is compressed enough to affect its motor function, the result is weakness of finger and wrist extension (a partial or complete inability to straighten the fingers), usually without sensory loss.

Superficial radial nerve (wrist) — numbness

When the sensory branch is compressed near the wrist (sometimes from a tight watch strap or handcuffs—”Wartenberg’s syndrome”), the result is numbness and tingling over the back of the thumb and hand, without weakness.

What causes radial nerve entrapment?

Causes include prolonged external pressure, a fracture of the humerus, repetitive forearm rotation and gripping, a direct blow, fibrous bands or a leash of vessels compressing the nerve, a ganglion or mass, and occasionally tight bands or straps at the wrist. Athletes, manual workers, and those doing repetitive twisting of the forearm are more prone to the forearm-level entrapments.

How is radial nerve entrapment diagnosed?

Diagnosis starts with the pattern of symptoms and a careful examination to localise the level of compression:

  • Nerve conduction studies and EMG — help confirm and localise a motor lesion (though they can be normal in the pain-only radial tunnel syndrome)
  • Ultrasound — images the nerve directly, showing swelling, compression, or a mass, and can guide an injection
  • MRI — shows nerve or muscle changes and excludes a compressing lesion
  • X-ray — where a fracture or bony cause is suspected

How is radial nerve entrapment treated?

Most cases are managed conservatively:

  • Removing the cause — relieving external pressure, modifying aggravating activity, and resting from repetitive forearm rotation
  • Splinting — a wrist splint supports a wrist drop and rests the forearm
  • Physiotherapy — nerve-gliding exercises, stretching, and strengthening as the nerve recovers
  • Surgery — decompression of the nerve, reserved for severe or persistent cases, or where there’s a clear compressing lesion

A pressure palsy (such as a Saturday night palsy) often recovers on its own over weeks to months once the pressure is removed.

Frequently asked questions about radial nerve entrapment

What is wrist drop?

Wrist drop is weakness of the muscles that straighten the wrist and fingers, so the hand hangs down and can’t be lifted at the wrist. It’s the hallmark of a high radial nerve compression — in the upper arm — often from a fracture of the humerus or prolonged pressure on the arm. Many pressure-related cases recover as the nerve heals.

What is Saturday night palsy?

It’s a radial nerve palsy caused by prolonged pressure on the nerve in the upper arm — classically from falling asleep with the arm draped over a chair or another person. It causes a temporary wrist drop, which usually recovers over weeks to months once the pressure is relieved and the nerve heals.

How is radial nerve entrapment different from tennis elbow?

One form — radial tunnel syndrome — is often confused with tennis elbow because both cause outer forearm and elbow pain. The clue is that radial tunnel pain is felt slightly farther down the forearm than the bony point of tennis elbow and is aggravated by resisted forearm rotation. Persistent “tennis elbow” that hasn’t responded may actually be radial tunnel syndrome.

Can radial nerve entrapment be treated without surgery?

Usually, yes. Removing the cause, splinting, physiotherapy, and sometimes an ultrasound-guided injection settle most cases, and pressure palsies often recover on their own. Surgery to decompress the nerve is reserved for severe or persistent cases, or where imaging shows a clear compressing lesion.

Final word from Sport Doctor London about radial nerve entrapment

Radial nerve entrapment covers a spectrum — from a wrist drop caused by high compression in the upper arm, to outer-forearm pain from radial tunnel syndrome, to numbness on the back of the hand from a wrist-level entrapment. The symptoms depend on where the nerve is trapped, so an accurate assessment to localise the level is the key to the right treatment. Most cases improve without surgery.

If you have forearm or hand weakness, numbness, or pain, Dr Masci can assess you in London, including ultrasound in clinic. Contact the team here or call +44 (0) 203 488 0350.

Other related nerve conditions: