The Effects of Hormonal Contraceptives on Incidence of ACL Injury Within Menstrual Cycle Phases

The aim of this study is to investigate how hormonal contraceptives affect ACL rupture incidence within menstrual cycle phases. It is thought hormones such as estrogen and progesterone (which fluctuate throughout the normal menstrual cycle) play a role in the laxity of ligaments within the body. It is hypothesised that around the time of ovulation the ACL undergoes increased laxity, leaving it more likely to be injured. This study will look at the phase of the menstrual cycle in which the ACL injuries occur and whether there are differences due to the use and type of hormonal contraception participants may be using (such as Combined oral contraceptive, Mirena, Implanon), which can modify the levels of circulating estrogen and progesterone. This study involves participants completing an anonymous electronic survey after presenting to a sports or orthopaedic clinic with an ACL rupture. The survey collects information about participant's current ACL injury and any previous knee injuries; typical menstrual cycle patterns and the use of hormonal contraception; and history of sports participation. Responses will be analysed to look for similarities and differences in ACL injury occurrence by menstrual cycle phase and hormonal contraceptive use. The study hypotheses are: 1. Hormonal contraceptives that are known to reduce ovulatory rises in estrogen will have the most consistent pattern of ACL rupture incidence across all phases of the menstrual cycle. 2. There will be a mitigated risk of ACL rupture in the preovulatory phase of the menstrual cycle, relative to the other phases, in women using hormonal contraception compared to those not using hormonal contraception 3. There will be a higher proportion of ACL ruptures during the preovulatory phase of the menstrual cycle in non-hormonal contraceptive users.