Sonographic reference values for median nerve cross-sectional area: A meta-analysis of data from healthy individuals

Abstract

Objective: Establish median nerve CSA reference values and identify patient-level factors impacting diagnostic thresholds.

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% CI] was 6.46mm² [6.09-6.84], 8.68mm² [8.22-9.13], and 8.60mm² [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=0.03mm², p=0.047). Men (9.42mm², [8.06-10.78]) had statistically larger proximal tunnel CSA (p = 0.03) as compared to women (7.71mm², [7.01-8.42]). No difference was noted in laterality.

Conclusion: A reference value for median nerve CSA in the carpal tunnel is 8.60mm². Adjustments may be required in pediatrics or older adults. The diagnostic threshold of 10.0mm² for male patients should be cautiously applied as the upper limit of normative averages surpasses this threshold.

Keywords: median nerve; meta-analysis; reference values; ultrasonography.

Figure 1.

Flow chart of studies through the search, screening, eligibility, and inclusion process.

Figure 2.

Forest plot of meta-analysis results showing the direction and magnitude of the weighted averages of median nerve cross-sectional area (CSA) in the proximal forearm 10cm or greater from the wrist across individual studies.

Figure 3.

Forest plot of meta-analysis results showing the direction and magnitude of the weighted averages of median nerve cross-sectional area (CSA) at the inlet to the carpal tunnel (CT) up to 4cm proximal to the radial carpal joint (i.e., distal wrist crease; 3a) and proximal CT at the level of the pisiform (3b) across individual studies.

Figure 3.

Forest plot of meta-analysis results showing the direction and magnitude of the weighted averages of median nerve cross-sectional area (CSA) at the inlet to the carpal tunnel (CT) up to 4cm proximal to the radial carpal joint (i.e., distal wrist crease; 3a) and proximal CT at the level of the pisiform (3b) across individual studies.

Figure 4.

Forest plots showing group differences for weighted averages of median nerve cross-sectional area (CSA) in the proximal carpal tunnel (CT) among studies that provided data stratified by sex demonstrating significantly larger CSA (p=0.03) in men (9.42mm²) than in women (8.58mm²).

Figure 5.

Forest plots showing group differences for weighted averages of median nerve cross-sectional area (CSA) in the proximal carpal tunnel (CT) among studies that provided data stratified by hand dominance (5a) or side (5b) demonstrating no differences based on laterality (p=0.92, p=0.41).

Figure 5.

Forest plots showing group differences for weighted averages of median nerve cross-sectional area (CSA) in the proximal carpal tunnel (CT) among studies that provided data stratified by hand dominance (5a) or side (5b) demonstrating no differences based on laterality (p=0.92, p=0.41).