The nerve/tunnel index: a new diagnostic standard for carpal tunnel syndrome using sonography: a pilot study.

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.