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Percentile-based diagnostic thresholds for median nerve inlet-to-outlet area ratio in ultrasound assessment of carpal tunnel syndrome

Mohamed Hamza

Egyptian Journal of Neurosurgery, 2026

90 participants

Abstract

Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy. Ultrasound assessment of the median nerve inlet-to-outlet area ratio (IOR) has demonstrated diagnostic value; however, commonly used fixed thresholds are often arbitrary and may not reflect normal population variability.

To derive percentile-based normative reference values for median nerve IOR in healthy controls and evaluate the diagnostic performance of percentile-derived thresholds for CTS.

This secondary exploratory cross-sectional analysis of a publicly available, de-identified dataset (Dryad; doi:

https://doi.org/10.5061/dryad.jt2sm

) included 90 participants (44 healthy controls and 46 electrodiagnostically confirmed CTS cases). Median nerve cross-sectional area was measured at the carpal tunnel inlet (pisiform level) and outlet (hamate level), and IOR was calculated as inlet/outlet. Distribution-free percentiles (5th–99th) were generated from the control group to establish reference limits. Diagnostic performance of percentile-based thresholds was evaluated using receiver operating characteristic (ROC) analysis, with optimal discrimination assessed using Youden’s index.

The 95th percentile control threshold (IOR > 1.318) provided the most balanced diagnostic performance, yielding sensitivity 91.3%, specificity 93.2%, positive predictive value 93.3%, negative predictive value 91.1%, and overall accuracy 92.2%. Discrimination was excellent (AUC 0.984; 95% CI 0.962–1.000). A percentile-anchored…

How strong is the evidence?

Evidence Hub reads this as a cross-sectional. Its evidence level is 4 of 5 (Low · observational). Observational designs can show an association but not prove cause. Reported size: 90 participants or records.

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