Radial Tunnel Syndrome

Radial Tunnel Syndrome

Authors, Editors, Case Information Author: Milan Oxspring, MD Affiliation: Mayo Clinic, Department of Physical Medicine and Rehabilitation Co Author(s): James B. Meiling, DO Senior Editor: Carlton Covey, MD, MEd Clinical Vignette: A 38-year-old right-handed male construction worker presented with chronic exertional dorsal right forearm pain. He had been experiencing these pain symptoms chronically for 5+ years and they were provoked with exertion, especially at his job with using jackhammers and saws. Symptoms were generally relieved with rest. Exam was notable for tenderness to palpation approximately 5cm distal of the lateral epicondyle on the dorsal side of the forearm, without any tenderness at the lateral epicondyle itself. Pain was reproduced with resisted wrist, finger, and thumb extension without focal weakness. Type of Probe Used: 4-18 MHz linear-array ultrasound transducer Unlabeled Long Axis View of the Deep Radial Nerve Proximal to the Radial Tunnel Unlabeled long axis view of the right deep radial nerve distal to radiocapitellar joint prior to the radial tunnel. Labeled Long Axis View of the Deep Radial Nerve Proximal to the Radial Tunnel Labeled long axis view of the right deep radial nerve distal to the radiocapitellar joint. The deep radial nerve (dashed lines) is seen to descend underneath the arcade of Frohse. There is focal enlargement of the nerve just prior to entering the radial tunnel in between the deep and superficial heads of the supinator muscle, indicating a site of peripheral nerve entrapment (arrows). The extensor carpi radialis longus (ECRL) and brachioradialis (BR) are seen superficial. Unlabeled Short Axis View of the Deep Radial Nerve Proximal to the Radial Tunnel Unlabeled short axis view of the right deep radial nerve just proximal to its entrance into the radial tunnel. Labeled Short Axis View of the Deep Radial Nerve Proximal to the Radial Tunnel Labeled short axis view of the right deep radial nerve just proximal to the entrance into the radial tunnel. There is focal enlargement of the deep radial nerve (dashed circle, cross-sectional area 7.16 mm2) just proximal to the radial tunnel, indicating entrapment of the peripheral nerve just distal to this site. The nerve is visualized as a hypoechoic circle with complete loss of intraneural fascicular architecture. Unlabeled Short Axis View of the Deep Radial Nerve Proximal to the Radial Tunnel with Doppler Unlabeled Short Axis View of the Deep Radial Nerve Proximal to Radial Tunnel with Doppler. Labeled Short Axis View of the Deep Radial Nerve Proximal to the Radial Tunnel with Doppler Labeled Short Axis View of the Deep Radial Nerve Proximal to Radial Tunnel with Doppler focal enlargement of the deep radial nerve (dashed circle) just proximal to the radial tunnel, indicating entrapment of the peripheral nerve just distal to this site. The nerve is visualized as a hypoechoic circle with complete loss of intraneural fascicular architecture. Vascularity can be seen around and in the fascial plane superficial to the nerve, representing the Leash of Henry. BR, brachioradialis; ECRL, extensor carpi radialis longus; ECRB, extensor carpi radialis brevis. Unlabeled Short Axis View of the Posterior Interosseous Nerve within the Radial Tunnel Unlabeled Short Axis View of the Posterior Interosseous Nerve within the Radial Tunnel. Labeled Short Axis View of the Posterior Interosseous Nerve within the Radial Tunnel Labeled Short Axis View of the Posterior Interosseous Nerve within the Radial Tunnel with mild flattening of the posterior interosseous nerve within the tunnel (dashed circle) between the two supinator heads. The nerve is visualized as a hypoechoic oval and is typically only seen as 1-2 fascicles within this area. BR, brachioradialis; ECRL, extensor carpi radialis longus; ECRB, extensor carpi radialis brevis. Unlabeled Short Axis View of the Posterior Interosseous Nerve Distal to the Radial Tunnel Unlabeled Short Axis View of the Posterior Interosseous Nerve Distal to the Radial Tunnel. Labeled Short Axis View of the Posterior Interosseous Nerve Distal to the Radial Tunnel Labeled Short Axis View of the Posterior Interosseous Nerve Distal to the Radial Tunnel. The nerve (dashed circle) runs adjacent to the recurrent radial artery (hypoechoic circle to the left of the nerve) and surrounded by all of the muscles it supplies innervation to. EDC, extensor digitorum communis; EDM, extensor digiti minimi; ECU, extensor carpi ulnaris; EPL, extensor pollicis longus; APL, abductor pollicis longus. #11 - Video View Video Short Axis Cine of the right deep radial nerve as it turns into the posterior interosseous nerve within the radial tunnel from proximal to distal. Focal enlargement of the deep radial nerve is seen as the nerve rapidly enlarges and then returns to a more normal size within the radial tunnel. Interpretation Image Interpretation: Prominent focal enlargement of the right deep radial nerve just proximal to its entrance into the radial tunnel. The nerve is focally hypoechoic with complete loss of intraneural fascicular architecture. Sonopalpation at this site reproduced the dorsal forearm symptoms. Within the radial tunnel, the posterior interosseous nerve (PIN) appears mildly flattened, returning to normal size distally. No abnormal Doppler signal was noted. Teaching Pearl: In the evaluation of deep radial nerve pathology, ultrasound should scan both proximal and distal to the arcade of Frohse. Findings that support entrapment include focal nerve enlargement, hypoechogenicity, loss of fascicular architecture, and a transition point or notch at the site of compression. Radial tunnel syndrome can coexist with lateral elbow tendinopathy or radiocapitellar pathology, so symptom reproduction with sonopalpation and full lateral elbow assessment can improve diagnostic confidence. References: 1. Basavaraj S, Raju V, Paraj D, Bhat AK, Acharya A. Role of high-resolution dynamic ultrasonography in the evaluation of posterior interosseous nerve compression at radial tunnel: a prospective case-control study. J Hand Surg Eur Vol. Published online April 26, 2026. doi:10.1177/17531934261443138 2. Xiao TG, Cartwright MS. Ultrasound in the evaluation of radial neuropathies at the elbow. Front Neurol. 2019;10:216. doi:10.3389/fneur.2019.00216 3. Kim Y, Ha DH, Lee SM. Ultrasonographic findings of posterior interosseous nerve syndrome. Ultrasonography. 2017;36(4):363-369. doi:10.14366/usg.17007
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