Radial tunnel syndrome

Radial tunnel syndrome is caused by compression of the posterior interosseous nerve (deep branch of the radial nerve) as it passes through the radial tunnel — a channel just past the lateral epicondyle that is bordered by the radial head, the extensor muscles, and the arcade of Frohse (a fibrous arch). Unlike lateral epicondylitis, the pain is located 4–5 cm distal to the lateral epicondyle over the radial head/neck, rather than at the epicondyle itself. True radial tunnel syndrome causes pain, not weakness; paralysis of finger/wrist extension indicates posterior interosseous nerve (PIN) syndrome, a more severe compression.

Lateral forearm pain distal to the lateral epicondyle, worsened by resisted middle finger extension (middle finger extension test) and resisted forearm supination. Distinguishing from lateral epicondylitis can be challenging — both cause lateral elbow pain. Diagnostic injection of local anesthetic into the radial tunnel (not the lateral epicondyle) confirms radial tunnel syndrome. MRI and EMG are often normal.

1. Radial tunnel injection

   Local anesthetic ± corticosteroid injection into the radial tunnel provides diagnostic and therapeutic benefit.

Radial tunnel syndrome that remains symptomatic after a structured trial of conservative treatment is considered for surgical decompression.

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