Comparative Analysis of Methods for Obtaining Median Nerve Cross-Sectional Area Using Ultrasound.

Abstract

Background: Ultrasound measurement of median nerve cross-sectional area (CSA) is widely used in carpal tunnel syndrome (CTS) diagnosis. This study compared 3 common measurement methods: A-B, Ellipse, and Trace to evaluate their reliability and accuracy.

Methods: Two observers (experienced hand surgeon and orthopedic surgery resident) measured median nerve CSA in 10 patients with suspected CTS. Each method was applied in standard and zoom-enhanced views: A-B method (measuring major/minor axes), Ellipse method (fitting ellipse to nerve boundaries), and Trace method (manually tracing nerve boundary). Measurements were compared to ImageJ software analysis as reference standard. Reliability and accuracy were assessed using intraclass correlation coefficients (ICCs), Bland-Altman analysis, and standard detectable difference (SDD).

Results: All methods showed high reliability (ICC: 0.940-0.994) but consistently underestimated CSA compared to ImageJ (12.15 ± 5.13 mm²). The Trace method showed smallest mean difference from ImageJ (-1.26 mm²), followed by A-B (-1.46 mm²) and Ellipse (-1.96 mm²). The Trace method demonstrated highest accuracy without zoom (85.5%) and lowest SDD (1.57 mm²). Interrater reliability was significantly higher in zoom condition for all methods, with Trace method showing highest interrater reliability in both zoom and nonzoom conditions.

Conclusion: All 3 ultrasound methods demonstrated high reliability in measuring median nerve CSA, with Trace method showing modest advantages in accuracy and precision. Zoom enhanced views improved interrater reliability but reduced measurement accuracy. Based on our findings, we recommend nonzoom Trace method for consistent longitudinal measurements, though maintaining proficiency in one selected method is more important. Further validation with larger studies is warranted.

Level of evidence: Level 2.