Girls and women seem to be at greater risk for anterior cruciate ligament (ACL) than their male counterparts. Women playing basketball and soccer are much more likely to injure their ACLs than men playing these same sports at the same level. Much research has gone into trying to understand the risk factors in order to prevent this potentially disabling injury.
Some studies have attempted to see if females are more likely to injure their knees at a particular time in the menstrual cycle. There are some reports that ACL tears are more likely at three points in the menstrual cycle: the preovulatory phase, follicular phase, and menstrual phase. Each of these phases has different changes in the type and levels of hormones circulating in the blood.
Since each normal menstrual cycle is approximately a month long, there may be a connection to the moon cycles. We are unaware of any scientific studies to prove or disprove this connection. Scientists have discovered receptor sites on the anterior cruciate ligament (ACL) for hormones such as estrogen and progesterone. Just the presence of these places for hormones to attach to cells suggests hormones may influence ligaments. But what the connection is or exactly how these hormones affect the ACL is a big unknown right now.