Manometric diagnosis of anal sphincter injuries.

A manometric technique of anal pressure vectography has been developed for the detection of anal sphincter injuries. Manometric symmetry of the anal sphincter can be visualized on the pressure vectorgram and quantified as a vector symmetry index. The mean vector symmetry index in asymptomatic women was 0.76, compared with 0.33 in incontinent women with a known sphincter injury (p = 0.0001). Among women who were incontinent without having a recognized sphincter injury, nearly half of those who had a previous episiotomy had subnormal (less than 0.60) vector symmetry indices (p = 0.0003). The values were in the same range as those from known injuries, suggesting the presence of an occult sphincter injury. In contrast, normal symmetry indices were found in all those who had never had an episiotomy or who presented with outlet constipation. We conclude that the vector symmetry index can expose occult anal sphincter injuries and may have a role in the selection of patients for sphincter repair.