Sonographic Reference Values for Median Nerve Cross-sectional Area: A Meta-analysis of Data From Healthy Individuals

Abstract

Objective: Establish median nerve cross-sectional area (CSA) reference values and identify patient-level factors impacting diagnostic thresholds. Materials and Methods: Studies were identified through a robust search of multiple databases, and quality assessment was conducted using a modified version of the National Institute of Health Study Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies. A meta-analysis was performed to identify normative values stratified by anatomic location. A meta-regression was conducted to examine heterogeneity effects of age, sex, and laterality. Results: The meta-analysis included 73 studies; 41 (56.2%) were high quality. The median nerve CSA [95% confidence interval, CI] was 6.46 mm2 [6.09–6.84], 8.68 mm2 [8.22–9.13], and 8.60 mm2 [8.23–8.97] at the proximal forearm, the carpal tunnel inlet, and the proximal carpal tunnel, respectively. Age was positively associated with CSA at the level of proximal carpal tunnel (β = 0.03 mm2, P = .047). Men (9.42 mm2 [8.06–10.78]) had statistically larger proximal tunnel CSA ( P = .03) as compared with women (7.71 mm2 [7.01–8.42]). No difference was noted in laterality. Conclusion: A reference value for median nerve CSA in the carpal tunnel is 8.60 mm2. Adjustments may be required in pediatrics or older adults. The diagnostic threshold of 10.0 mm2 for male patients should be cautiously applied as the upper limit of normative averages surpasses this threshold.