The Correlations between Estradiol, Estrone, Estriol, Progesterone, and Sex Hormone-Binding Globulin and Anterior Cruciate Ligament Stiffness in Healthy, Active Females

BACKGROUND: Injury to the anterior cruciate ligament (ACL) often requires surgery and extensive rehabilitation. Women who participate in collegiate sports and military drills are more likely to injure their ACL than are men participating in similar activities. The influence of the normal fluctuation of sex hormones on the physical properties of the ACL is one potential cause for this disparity. The purpose of this study was to report the correlation between estradiol, estrone, estriol, progesterone, and sex hormone binding globulin (SHBG) and ACL stiffness during three phases of the menstrual cycle in normally cycling, healthy females. METHODS: We tested ACL stiffness and collected blood from 20 female subjects who were not using oral contraception during three phases of their menstrual cycle. Ligament stiffness was tested with the KT-2000 trade mark knee arthrometer (MEDmetric, San Diego, CA). Concentrations of estradiol and SHBG were assessed via radioimmunoassay (RIA). Progesterone, estriol, and estrone concentrations were determined via enzyme-linked immunoassay. RESULTS: Spearman rank correlation analysis indicated a significant correlation between estradiol concentration and ACL stiffness (-0.70, p < 0.001) and estrone concentration and ACL stiffness near ovulation (0.46, p = 0.040). With the effects of the other variables controlled, there was a significant partial correlation between estradiol (-0.80, p < 0.001), estriol (0.70, p = 0.003), and progesterone (0.66, p = 0.005) and ACL stiffness near ovulation. CONCLUSIONS: Our results indicate that there is a significant correlation between estradiol, estriol, and progesterone and ACL stiffness suggesting that fluctuating levels of sex hormones may influence the stiffness of the ACL near ovulation. Future studies that examine the relationship between sex hormones and the physical properties of the ACL should be focused near the ovulation phase of the menstrual cycle.