A GENDER-SPECIFIC WRIST RATIO AND THE LIKELIHOOD OF A MEDIAN NERVE ABNORMALITY AT THE CARPAL-TUNNEL

The objective of this study was to clarify the significance of the association of the patient wrist ratio and a median abnormality at the carpal tunnel. The average wrist ratio and median nerve latencies were determined in 665 patients with symptoms involving at least one hand or forearm. The mean average wrist ratio of the 419 women (0.690) exceeded that of the 246 men (0.672), differing significantly (mean difference 0.018; 95% confidence interval, 0.012 to 0.024; P < 0.0001). The mean average wrist ratio of the 236 women (0.704) with a median abnormality exceeded that of the 183 women (0.672) without a median latency abnormality (difference 0.032; 95% confidence interval, 0.026 to 0.038; P < 0.0001); the mean average wrist ratio of the 166 men (0.681) with a median abnormality exceeded that of the 80 men (0.655) without a median latency abnormality (difference 0.026; 95% confidence interval, 0.016 to 0.035; P < 0.0001). Regression analyses revealed an increasing average wrist ratio to correlate positively with a slowing of the dominant hand median nerve motor and sensory latencies, with the best latency correlation being the median minus the ulnar palm-to-wrist latency difference in the women (r = 0.394, P < 0.0001) and in the men (r = 0.329, P < 0.0001). A median abnormality was found in 79% of the women and in 86.9% of the men with an average wrist ratio of 0.7 or greater; women had 73.8% of the average wrist ratios of 0.7 or greater. The patient wrist ratio (and related factors) seems a vital yet confounding variable relative to much of the previous epidemiologic investigation of the carpal tunnel syndrome, and may be a key element in explanation of the greater prevalence of a median neuropathy at the carpal tunnel in women and the tendency of a bilateral occurrence of the condition.