Association of a posterior fourchette finding with other evidence of sexual abuse in prepubertal females

BACKGROUND: We have noted a clinical finding in the genital exam of prepubertal females which has not been previously reported in the literature: thinning or diminution of the posterior fourchette. OBJECTIVE: To determine whether thinning of the posterior fourchette is associated with child sexual abuse. METHODS: We performed a case-control study of girls referred to an inner-city public hospital child protection center evaluating 200-250 new patients/year. Logbooks recording every patient seen in the center were used to identify cases and controls. Cases were all 3 to 11 year old prepubertal females who were seen for a sexual abuse evaluation between 1995 and 2000 who had posterior fourchette thinning. Controls were all prepubertal females seen during the study period who matched cases on age, date of visit, ethnicity and examiner, but had normal posterior fourchettes. Medical records were reviewed to confirm eligibility and supplement information about subject disclosure of sexual abuse and physical findings. Cases and controls were compared for evidence of sexual abuse, defined as disclosure of sexual abuse and/or abnormal hymenal findings (transection or thinning). As per protocol, determination of all genital findings was made by 1 of 2 examiners blinded to details of the patients disclosure. RESULTS: 475 girls age 3 to 11 (pubertal and prepubertal) were evaluated for possible sexual abuse. There were 37 cases who were prepubertal with a thinned posterior fourchette, and 89 matched controls. Included in this analysis were the 32/37 cases (86%) and 81/89 controls (91%) with complete data (range 1-4 controls per case). 87.5% of cases had evidence of sexual abuse compared to 24.7% of controls (OR = 21.14, p < .001). These results remained significant even after excluding the 19 cases and 4 controls with abnormal hymenal findings (69.2% vs 20.8%, OR = 8.6, p = .001). In a multiple logistic regression adjusting for age, ethnicity, examiner and date of visit, cases were significantly more likely than controls to have evidence of sexual abuse (adjusted OR = 22.8, p < .001). CONCLUSIONS: In a case-control study of prepubertal girls, thinning of the posterior fourchette was associated with evidence of sexual abuse. Confirmation of these results will require prospective study.