Role of high-resolution dynamic ultrasonography in the evaluation of posterior interosseous nerve compression at radial tunnel: a prospective case-control study

INTRODUCTION: Radial tunnel syndrome is a dynamic compressive neuropathy of the posterior interosseous nerve often misdiagnosed as lateral epicondylitis. This study aimed to appraise the role of high-resolution dynamic ultrasonography in diagnosing radial tunnel syndrome by assessing nerve compression in different forearm positions. METHODS: In this prospective case-control study, 28 patients with radial tunnel syndrome and 56 matched healthy volunteers underwent dynamic ultrasonography. The anteroposterior (AP) diameter and cross-sectional area (CSA) of the posterior interosseous nerve were measured proximal to the Arcade of Frohse and the AP diameter was measured within the tunnel in the pronated, neutral and supinated forearm positions. The measurements were compared with those of the volunteers and the unaffected side of the patients. RESULTS: An increase in the AP diameter in both the pronation and neutral forearm positions, as well as a larger CSA during forearm pronation, was observed proximal to the Arcade of Frohse in patients compared with volunteers. The increase in the AP diameter within the radial tunnel was significant in all three forearm positions. Comparison of the affected and unaffected sides revealed posterior interosseous nerve compression, with an increased AP diameter in the neutral forearm position. Twenty-five patients who were recalcitrant to non-operative treatment underwent surgical decompression and the Arcade of Frohse was the most common site of compression. At the 12 month follow-up, 24 patients achieved excellent to good results. CONCLUSION: Dynamic ultrasonographic assessment of changes in the AP diameter and CSA is an effective diagnostic tool for identifying radial tunnel syndrome. Although the Arcade of Frohse is the primary site of compression, it is crucial to address all compression structures in the radial tunnel during surgery. LEVEL OF EVIDENCE: IV.