Scientists have long speculated that female hormones play a role in this and that there must be a particular phase of the cycle during which women were more vulnerable to injury.  

Recent studies published in British Journal of Sports Medicine and The American Journal of Sports Medicine did indeed find increases in joint laxity as a result of hormonal shifts throughout the month – but the laxity occurred in different parts of the menstrual cycle for different women. 

Researchers now theorize that there is indeed a connection between female hormonal fluctuations and ACL injuries, but unfortunately it may not be in predictable “one-size-fits-all” way. 

Some other reasons that women are more likely to experience ACL tears include:

• Women have a more narrow space (called the intercondylar notch) for the ACL to move within making it more likely that ends of the femur bone (the femoral condyles) could pinch the ACL and rupture it. 
• Women have a wider “quadriceps angle” (aka “q angle”).  The q angle is the angle at which the femur (or upper leg bone) meets the tibia (or lower leg bone).  Because females have a wider pelvis there femure comes in at more of an angle relative to their tibia, which means more force on the ligaments of women’s knees whenever the knee twists.  
• In general, women have looser muscles, tendons and lligaments than men (again because of those darned hormones!) potentially providing less protection from rotational forces.
• Women have less muscle strength relative to bone size than men do, meaning that the ACL needs to work harder in women to keep in the knee aligned properly. 
• Women are often not encouraged to participate in sports as young girls and/or to the extentthat young boys are and therefore may not develop the muscular coordination, proprioception and reflexes as well, making them less able to handle the stresses of competitive play much later on in their physical maturation.  (Even more reason to get girls playing sports earlier!)

Coming up next…more on what the ACL does and what you can do to reduce your risk of injury.