Where it is, and two different problems
Just above the elbow, the radial nerve divides into a branch that carries feeling to the back of the hand and thumb, and a deep branch, the posterior interosseous nerve, which carries no feeling from the skin but powers the muscles that straighten the wrist, fingers and thumb. The deep branch runs through a channel of muscle and fibrous bands in front of the elbow (the radial tunnel) and passes under the edge of the supinator muscle, at a fibrous arch called the arcade of Frohse. Across 13 published series, that arch was where surgeons most often found it squeezed.
Radial tunnel syndrome is pain without weakness or numbness. Weakness of the muscles that straighten the fingers and thumb (a finger drop) is a different problem, posterior interosseous nerve syndrome, which a neurologist's review says is usually easy to identify because of the weakness.
Sources 1, 2, 3, 4, 5, 6
Why it's debatedMixed evidence
It was first described in people whose tennis elbow hadn't settled, with pain and tenderness over the supinator muscle but no weakness, by analogy with carpal tunnel syndrome. A neurologist's review argues that 'it is debatable whether radial nerve entrapment causes the forearm discomfort', and a reference text notes that some experts question whether it exists at all.
Across 13 published series (391 arms), definitions varied, nerve tests were abnormal in only 8.9% of 327 arms, three-quarters of the series used a test injection to make the diagnosis, and many people also had tennis elbow, which makes results hard to compare. One surgical series concluded that the usual signs may be unreliable, and another cast doubt on whether nerve compression causes this kind of elbow pain. Surgeons who treat it argue that it is a real diagnosis, made from where the pain is, what it feels like and the tests that provoke it. So it is a label for a pattern of pain, usually used when tennis elbow care hasn't worked, and experts disagree about it.
Sources 6, 2, 4, 7, 8, 9
How common it is, and the overlap with tennis elbowEmerging evidence
In a US insurance database, 75,459 people had the diagnosis: about 9 in 100,000 people a year, at an average age of 52, and 55% were women. A review gives about 0.03% of people a year, against 0.1% to 0.35% for carpal tunnel syndrome.
The two can overlap: 5.7% of people in the database also had tennis elbow on the same side within 6 months, and US orthopaedic surgeons say it can occur at the same time as tennis elbow. In one small study of 32 people with tennis elbow lasting over 6 months, a nerve-blocking injection pointed to radial tunnel syndrome in 44%. That is one small study, so the size of the overlap is uncertain.
Sources 10, 3, 11, 12
How it feels, and how clinicians tell it from tennis elbowEmerging evidence
An aching or sharp pain on the top of the forearm and the outer elbow, brought on by straightening the wrist and fingers, turning the palm up, gripping and lifting. Numbness is rare, because the nerve at this level mainly powers muscles.
Where it's tender: tennis elbow is tender on the bony bump; radial tunnel syndrome is most tender about 3 to 5 cm below it, over the muscle. What provokes it: turning the palm up against resistance, and straightening the middle finger against resistance. Tennis elbow doesn't cause tenderness along the nerve. A local anaesthetic injection into the tender spot that takes the pain away supports the diagnosis. A placebo-controlled trial required 4 of 5 signs: pain with activity, tenderness 3 to 5 cm below the bump, pain worse turning the palm up, pain spreading down the back of the forearm, and a positive result on one more examination test.
Sources 1, 3, 13, 14, 4
What tests and scans do and don't showEmerging evidence
Nerve conduction tests are generally inconclusive: abnormal in 8.9% of arms in published series, and normal in all 32 people in the nerve-block study. A normal test doesn't rule it out, and an abnormal one points to weakness of the nerve or another diagnosis. MRI (magnetic resonance imaging) is usually normal, though in 25 people suspected of it, 13 had swelling or wasting in the muscles the nerve supplies, and 2 of 10 healthy volunteers had borderline findings. Ultrasound looked promising in a small pilot study, but in the 32-person study the size of the nerve didn't separate those with and without a positive nerve block. No single test confirms it.
Sources 4, 3, 12, 15, 16
Look-alikes
Most of these have their own guides on this site.
- Tennis elbow: pain on the bony bump, worse gripping and lifting with the wrist. The two often sit together.
- A pinched nerve in the neck: pain spreading from the neck, changed by moving the neck, often with tingling.
- Posterior interosseous nerve palsy: weakness straightening the fingers or lifting the thumb. See a GP promptly.
- Burning or tingling over the back of the thumb and hand: the radial nerve's other branch, the one that carries feeling (Wartenberg's syndrome). Our brachioradialis muscle guide covers it.
- A lump pressing on the nerve: ganglia, fatty lumps and, rarely, bone tumours.
- Intersection syndrome: pain and creaking further down, a few finger-widths above the wrist.
Sources 1, 6, 2
How it usually goesEmerging evidence
It hasn't been well studied. In the placebo-controlled trial, pain and disability improved over 3 months in both groups, including those given a saline injection. In a series of 40 people given one steroid injection, 23% went on to surgery within a year. A review notes that non-surgical care is often tried for a long time, often a year.
Sources 13, 17, 3