Added Value of Wrist-to-Forearm Ratio to Single Measurement of Median Nerve Cross-Sectional Area for Diagnosis of Carpal Tunnel Syndrome.

PURPOSE: The purpose of this study was to evaluate whether utilization of wrist-to-forearm ratio (WFR) improves the diagnostic performance of ultrasound beyond the wrist cross-sectional area (CSA) alone.

METHODS

Prospective observational cohort study of patients evaluated for carpal tunnel syndrome in a hand surgery clinic. Median nerve CSA was measured at the carpal tunnel inlet and proximal forearm, and WFR was calculated. Carpal tunnel syndrome (CTS)-6 score and chart-documented clinical diagnosis served as reference standards. Demographic variables were obtained by retrospective chart review. Diagnostic performance of CTS-6, CSA, and WFR was assessed using Receiver operating characteristic analysis. Mixed-effects logistic regression evaluated the incremental value of WFR beyond CSA. Alternative WFR thresholds (1.6-2.0) were analyzed.

RESULTS

A total of 113 patients (196 wrists) were included; 113 wrists (57.7%) were clinically diagnosed with CTS. Mean age was 56.4 ± 16.0 years, and 50.4% were female. WFR ≥ 1.4 classified 76.5% of wrists as positive compared with 67.3% for wrist CSA ≥ 10 mm2 and 44.9% for CTS-6 ≥12. CTS-6 demonstrated excellent discrimination (area under the curve [AUC] 0.977), wrist CSA good discrimination (AUC 0.813), and WFR weak discrimination (AUC 0.623). Adding WFR to models, including CTS-6 and wrist CSA, did not improve diagnostic performance. CSA misclassified 51 wrists; WFR reclassified 21 (41%) but resulted in more incorrect classifications overall. Increasing WFR thresholds improved specificity but reduced sensitivity, with no improvement in overall diagnostic performance.

CONCLUSIONS

CTS-6 demonstrated excellent diagnostic discrimination in this cohort, and wrist CSA demonstrated good standalone ultrasound performance. WFR did not provide meaningful incremental diagnostic value beyond wrist CSA when clinical diagnosis was used as the reference standard.

CLINICAL RELEVANCE: As ultrasound becomes more integrated into clinical practice, hand surgeons should be aware of the relative utility of different measurement techniques for diagnosing carpal tunnel syndrome.