Radial Tunnel Syndrome

Radial tunnel syndrome is when one of the deep nerves of the forearm gets squeezed as it passes through a narrow channel just past the outer elbow. The channel is the radial tunnel, walled in by the bony radial head, surrounding muscles, and a tight fibrous arch (the arcade of Frohse). The squeezed nerve causes a deep, aching pain in the outer forearm. The classic confusion is with tennis elbow — both cause pain on the outer side of the elbow. The tell-apart: tennis elbow hurts right at the bony bump on the outside of your elbow; radial tunnel hurts about 2 inches further down your forearm. True radial tunnel syndrome causes pain only, not weakness — if your fingers or wrist also stop working, that's a more severe nerve compression with a different name (PIN syndrome).

• Deep, aching pain in the outer forearm — not right at the elbow bump, but about two inches further down the forearm, in the muscle belly.
• Pain with twisting and gripping — turning a doorknob, wringing a towel, or using a screwdriver brings on the ache.
• Worsening with repetitive forearm use — the pain builds during sustained gripping or twisting activities and may linger for hours afterward.
• No numbness or tingling — unlike many nerve problems, radial tunnel syndrome causes pain only, not the pins-and-needles you'd expect from a pinched nerve.
• Resemblance to tennis elbow that doesn't respond to tennis elbow treatment — if you've been treated for lateral epicondylitis without improvement, this may be the real diagnosis.

Pain in the outer forearm a couple inches past the elbow that gets worse when you extend your middle finger against resistance (the middle finger extension test) or rotate your palm upward against resistance. Telling it apart from tennis elbow is the hard part because both hurt around the outer elbow. The most reliable test: a numbing injection placed precisely into the radial tunnel — if your pain disappears for the few hours the medicine works, that confirms the nerve is the culprit. MRI and nerve-conduction tests usually look normal in this condition.

1. Radial tunnel injection

   An ultrasound-guided injection of numbing medicine — sometimes paired with a steroid — placed precisely into the radial tunnel does double duty: it confirms the diagnosis (your pain disappears for a few hours) and often quiets the pain for a longer stretch.

If a long, structured trial of activity changes, therapy, and injections hasn't quieted the pain, surgical decompression — a small operation that opens the tight fibrous arch and frees the nerve from anything pressing on it — is the next step.

External patient-education references and related OSI pages for additional background:

• Britannica — Joint (anatomy)
• AAOS OrthoInfo — patient education library
• OSI glossary — orthopedic terminology in plain language