New Ultrasonographic Parameter for Diagnosing Carpal Tunnel Syndrome: The Median Nerve-to-Ulnar Artery Cross-Sectional Area Ratio

<i>Background and Objectives:</i> Carpal Tunnel Syndrome (CTS) is the most common entrapment neuropathy. Ultrasonography is a widely used diagnostic method for CTS, and the median-to-ulnar nerve cross-sectional area ratio (MUR) is a well-known parameter. However, the ulnar nerve may be affected by various conditions of the median nerve; therefore, we considered finding further parameters. The aim of the study is to identify the correlation between the median nerve-to-ulnar artery cross-sectional area ratio (MUAR) and existing ultrasonographic parameters used as diagnostic indicators of CTS. <i>Materials and Methods:</i> Sixty-seven wrists from forty-two patients who were diagnosed with CTS by electrodiagnostic studies within 4 years before enrollment were retrospectively analyzed in this study. The median nerve cross-sectional area (CSA), ulnar nerve CSA, and ulnar artery CSA at full dilation were measured. In addition to well-defined CTS ultrasonographic parameters, the MUAR were calculated. All measurements were gathered at three levels. The reproducibility was evaluated through intraclass correlation coefficients (ICCs) and Bland-Altman plots. <i>Results:</i> The MUAR at the carpal tunnel inlet showed a strong positive correlation with the MUR at the same level (<i>ρ</i> = 0.738, <i>p</i> < 0.05) and the median nerve wrist forearm ratio (<i>ρ</i> = 0.541, <i>p</i> < 0.05). In addition, the MUAR at the carpal tunnel outlet presented a strong positive correlation with MUR at the carpal tunnel inlet (<i>ρ</i> = 0.528, <i>p</i> < 0.05). The MUAR at 12 cm proximal to the distal wrist crease showed a strong positive correlation with the MUR at the corresponding level (<i>ρ</i> = 0.613, <i>p</i> < 0.05). Intra-rater and inter-rater reliability showed a high degree of agreement (ICCs > 0.90). <i>Conclusions:</i> This study demonstrates correlations between known CTS parameters and MUAR and suggests the possibility of MUAR as a reliable CTS diagnostic tool. Further research is recommended to validate these findings.