The Association of Salivary Estradiol Levels with Anterior Cruciate Ligament Stiffness and Laxity

BACKGROUND: Females are three to six times more likely to sustain an anterior cruciate ligament (ACL) injury than males. Researchers have previously identified hormonal fluctuations as a possible intrinsic factor related to the higher incidence of ACL injuries among female athletes. Whether hormonal levels, with or without use of oral contraceptives (OC), influence ligamentous mechanical properties resulting in increased ACL injury risk remains unclear. Furthermore, previous studies have mainly focused on anterior tibial translatory (ATT) laxity, with limited research on changes in ATT tissue compliance/stiffness. The purpose of this study is to investigate the influence of estradiol levels, menstrual cycle phases, with and without use of OC on ATT tissue compliance/stiffness and laxity. METHODS: Fifty-two female participants (age 24-30 years), divided into two groups of 26 each (Group OC using oral contraception, and Group NOC not using oral contraceptive). Data collection was performed on two different dates corresponding to two menstrual cycle phases: follicular or inactive phase (days 1-3) and the ovulation or active pill phase (days 12-14). Estradiol levels via saliva sampling, ATT tissue compliance/stiffness and laxity measures via the GNRB knee arthrometer were collected each testing session. Spearman’s rank-order correlation product-moment correlations were run to determine the relationship between follicular and ovulation phase estradiol and GNRB outputs related to translation and compliance. RESULTS: Estradiol levels showed a significant change between follicular and ovulation phases across both groups combined (p = 0.01). There were weak non-significant correlations between measured estradiol levels and GNRB measures of anterior translation and compliance, (p> 0.05). No significant relationships were found across subjects whether they were on oral contraceptive or not using hormone regulated birth control. CONCLUSION: Estradiol level changes in the follicular and ovulation phases and oral contraceptive use did not significantly influence ACL laxity (anterior tibial translation) or compliance/stiffness. Additional studies on hormonal fluctuations as a potential risk factor for higher female ACL injury are indicated.