Strength-duration testing of the external anal sphincter in females with anorectal dysfunction.

PURPOSE: The strength-duration test has been suggested as a means of assessing external anal sphincter function. This study was designed to investigate this claim by comparing the strength-duration test with established measures of external anal sphincter function. METHODS: Forty-nine females undergoing diagnostic anorectal testing (manometry, rectal sensation, electromyogram, pudendal nerve terminal motor latency, and endoanal ultrasound) also had the strength-duration test performed (which was repeated for each patient after a short rest period). RESULTS: The strength-duration test was repeatable. Statistically significant correlations were found between this test at pulse durations of 3 ms, 1 ms, and 0.3 ms with electromyographic activity of the external anal sphincter and with pressure in the anal canal during voluntary contraction. Significant correlations were found for durations of 100 ms, 30 ms, 10 ms, and 3 ms with the pudendal nerve terminal motor latency on the right and for the 3 ms and 0.3 ms durations with latency on the left. There were no correlations between the strength-duration test and resting pressure in the anal canal. CONCLUSION: The strength-duration test significantly correlates with the established measures of external anal sphincter function and its innervation. Therefore, this simple test appears to provide a simple measure of external anal sphincter denervation.