Relationship between anthropometric variables and the cross-sectional area of the median nerve by ultrasound assessment in healthy subjects.

Objective: Ultrasound study of the wrist in patients with suspected entrapment syndrome has severe limitations due to the variability of what is considered normal for the cross-sectional area of the median nerve and where to proceed to measure it. We aim to determine the extent to which different anthropometric variables influence the median nerve area in subjects without carpal tunnel syndrome.

Methods: We conducted an observational study based on a multivariate linear regression analysis using as a dependent variable the area of the median nerve cut at two specific points in the wrist of healthy subjects. The independent variables were sex, age, height, weight, body mass index, finger flexor strength, and carpal circumference.

Major results: The measurements of the median nerve cross-sectional area were normalized using a quadratic fixing procedure. Of all the variables included in the linear regression analysis, only carpal circumference and sex (0: female, 1: male) contributed significantly in the final model using the wrist crease as the measurement point (Constant B=-209.45, carpal circumference coefficient=21.07, sex coefficient 10.87). At four centimeters distal to the carpal fold, the model included the same variables (Constant B=-221.84, carpal circumference coefficient=24.01, and sex coefficient=11.41).

Conclusion: Both the wrist circumference and the sex are variables that should be considered to determine cut-off points of normality in future validation studies about the cross-sectional area of the median nerve.