Ultrasonographic and Electrophysiologic Assessment of Radial Tunnel Syndrome in Patients with Treatment-Resistant Lateral Epicondylitis: Insights into Diagnostic Utility and Clinical Implications.

To evaluate radial tunnel syndrome (RTS) in patients with treatment-resistant lateral epicondylitis (LE) and assess the diagnostic utility of ultrasonographic, electrophysiologic, and clinical evaluations. In this cross-sectional study, 32 patients with LE persisting for at least 6 months underwent comprehensive clinical, electrophysiological, and ultrasonographic assessments. RTS diagnosis was established using an ultrasound-guided posterior interosseous nerve (PIN) block as the reference standard and compared with diagnostic criteria based on nerve cross-sectional area (CSA) threshold values and side-to-side CSA comparison. Pre- and post-block pain levels during clinical tests were also analyzed. RTS was diagnosed in 44% of patients using the injection test. The mean CSA of the PIN was larger on the symptomatic side but did not differ significantly between RTS-positive and RTS-negative cases. Electrophysiological findings were normal in all patients, and LE ultrasound findings did not vary based on the presence of RTS. Agreement between RTS diagnosis and US-CSA comparison with the contralateral side was slight (κ = 0.138; p = 0.4024), while threshold values showed no agreement (κ = 0.098; p = 0.118). Cozen's test demonstrated the highest reliability, with significant pain reduction following the block. RTS frequently coexists with treatment-resistant LE. Comparing PIN-CSA with the asymptomatic side, along with the US-guided PIN block, enhances diagnostic accuracy.