Sex differences in the volumetric relationship between the median nerve and carpal tunnel in healthy adults: A three-dimensional MRI study.

Abstract

Carpal tunnel syndrome (CTS) occurs more frequently in women than in men; however, the anatomical basis for this sex difference remains unclear. Conventional two-dimensional assessments, such as cross-sectional area (CSA) measurements, are limited to single slices and may not accurately represent whole-tunnel morphology. This study aimed to quantify the three-dimensional volumetric characteristics of the median nerve and carpal tunnel using MRI in healthy adults and to investigate sex-related anatomical differences. Seventy-nine healthy adults (36 men and 43 women) underwent three-dimensional wrist MRI, and median nerve volume (MNV) and carpal tunnel volume (CTV) were quantified. The volumetric nerve-to-tunnel ratio (MNV/CTV) was calculated and compared between sexes. For comparison, CSA measurements were obtained at the pisiform and hamate levels. Sex-related differences and the influence of potential confounding factors were evaluated. Men had significantly larger MNV and CTV than women. In contrast, the MNV/CTV ratio was significantly higher in women overall. Level-specific analyses showed a significant sex difference in MNV/CTV at the hamate level but not at the pisiform level. After adjustment for age, body mass index (BMI), and occupational workload, sex remained independently associated with MNV/CTV. Strong correlations were observed between three-dimensional volumetric measurements and CSA measurements of the median nerve. Three-dimensional MRI identified sex-related differences in relative median nerve occupancy within the carpal tunnel in healthy adults. These findings suggest that volumetric assessment provides complementary anatomical insight beyond conventional CSA measurements and may partly contribute to understanding the higher prevalence of CTS in women.