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.

Anterior Cruciate ligament (ACL) rupture has been observed at higher rates in females than males during sporting competition, particularly during the preovulatory phase of the menstrual cycle. During the menstrual cycle, estrogen secretion varies from 10 to 100 fold throughout the cycle. A possible explanation for the ACL injuries being observed in the preovulatory phase, is that increases in estrogen levels increases the laxity of the ACL, predisposing it to risk of rupture. Studies investigating knee joint laxity, concluded that increased joint laxity was associated with an increased risk of ACL injury. In addition, measurement of knee laxity found no changes in laxity over time in males, but greater anterior displacement of the knee during the preovulatory phase of the menstrual cycle compared with the ovulatory and postovulatory phases in women.

Use of hormonal contraception typically maintains estradiol levels at ~25 pg/ml and decreases the ovulatory rise in estrogen. A study of the use of hormonal contraceptive in alpine skiers with ACL rupture reported that 74% of women were in the preovulatory phase (vs 26% in the postovulatory), experienced an ACL rupture. However, in women with ACL rupture in the preovulatory phase, 72.5% of the women were not using a hormonal contraceptive. A recent systematic review suggested an association between hormonal fluctuations and ACL injury and that hormonal contraceptives offer 20% reduction in risk of injury. Multiple modalities of hormonal and contraceptive control are available to females within Australia, but the efficacy of different hormonal contraceptives for reducing the risk of ACL rupture is unknown.

This study aims to investigate: 1) whether there are differences in risk of an ACL rupture incidence within menstrual cycle phases in females using different types of hormonal contraception. 2) whether there are differences in the pattern of ACL rupture incidence within menstrual cycle phases in females using vs not using hormonal contraception. 3) whether ACL rupture incidence in female athletes not using hormonal contraceptives are more prevalent during the pre-ovulatory phase of the menstrual cycle.

The study will use a cross-sectional design, with data being collected in women presenting at sports medicine or orthopaedic clinics with ACL rupture. On presentation at the clinic with ACL rupture, the study will be introduced to patients by a clinician and they will be shown a recruitment flyer that includes a QR code. On scanning the QR code patients will be taken to a RedCap survey website that they can enter an email in to receive, via automated reply email, a Participant Information Sheet and link to an anonymous study survey. The survey will take approximately 7 minutes to complete and asks questions about how the participants ACL injury occurred, any previous knee injuries, their menstrual cycle phase that the injury occurred in, their usual menstrual cycle characteristics, their use of hormonal contraceptives and the main sport they play.

Injury data will be analyzed according to menstrual cycle phase to confirm whether the preovulatory phase presents higher risk of ACL rupture than the ovulatory/postovulatory phase. Data will be stratified by hormonal contraception use and type to evaluate whether the injury occurrence pattern within the menstrual cycle differs by hormonal contraceptive use, such that the anticipated higher incidence in the preovulatory phase is mitigated with hormonal contraceptive use (and type).

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.

Inclusion Criteria:

• Presenting to a sports or orthopaedic clinic with an acute ACL rupture of their knee that occurred within the last 3 months

Females who present to a sports or orthopaedic clinic with an ACL rupture that occurred within the previous 3 months

Data to be made available on request