OBJECTIVES: To define the relationship between body indices of healthy adults 
and cross-sectional areas of the carpal tunnel and median nerve and to obtain 
the nerve/tunnel index, which represents a new standard for diagnosing carpal 
tunnel syndrome using sonography.
METHODS: Body indices (height, weight, and body mass index) were analyzed in 60 
healthy adults, and electromyography and sonography were also performed. The 
cross-sectional areas of the proximal and distal median nerve and carpal tunnel 
were obtained by sonography. The proximal and distal nerve/tunnel indices were 
obtained by calculating the ratio between the proximal and distal 
cross-sectional areas of the median nerve to those of the carpal tunnel and 
multiplying the value by 100.
RESULTS: Although the proximal cross-sectional areas of the median nerve and 
body indices showed statistically significant relationships with weak positive 
correlations, the proximal and distal areas of the carpal tunnel showed 
relatively stronger correlations with body indices. Between sexes, there were 
significant differences in the proximal median nerve cross-sectional area (mean 
± SD: male, 10.48 ± 3.21 mm(2); female, 8.81 ± 3.21 mm(2); P < .05) and proximal 
carpal tunnel area (male, 182.50 ± 21.15 mm(2); female, 151.23 ± 21.14 mm(2); P 
< .05). There was no difference in the proximal nerve/tunnel index (male, 5.80% 
± 1.72%; female, 5.91% ± 1.63%). There was a statistically significant 
difference in the distal carpal tunnel cross-sectional area (male, 138.90 ± 
20.95 mm(2); female, 121.50 ± 18.99 mm(2); P < .05) between sexes, but the 
distal median area (male, 9.99 ± 3.42 mm(2); female, 8.46 ± 1.84 mm(2)) and 
distal nerve/tunnel index (male, 7.15% ± 2.00%; female, 7.01% ± 1.38%) showed no 
significant differences. The proximal index was significantly higher than the 
distal index (proximal, 5.85% ± 1.66%; distal, 7.08% ± 1.71%).
CONCLUSIONS: The nerve/tunnel index is unaffected by body indices or sex and 
thus may be a useful and objective standard for diagnosing carpal tunnel 
syndrome.