Females do appear to be at greater risk for anterior cruciate ligament (ACL) injuries than men. Many studies have been done to find out why this is happening.
Here's what we know so far. First of all, more and more females of all ages are participating in sports. The very nature of athletic involvement increases anyone's risk of injury regardless of gender. Overall, there are more ACL injuries among men but there are also more men in competitive sports.
Some studies have looked at the size, shape, and position of the female pelvis in relation to the knee joint as a potential factor in ACL injuries. Altered stresses, load, and force on the joint from these anatomical features may play a role in ACL injuries among women.
Others are investigating the role of neuromuscular control. This refers to how well the muscles around the knee compensate for any intrinsic (already present) deficiency of the ACL.
When comparing males to females, men generate greater muscular stiffness around the knee joint. They recruit muscles in a different pattern than women. It may be the case that women's natural movement doesn't allow for the intense athleticism required in today's competitive sports.
The best evidence available shows that improving strength, motor control, and proprioception (sense of joint position) may be the best prevention policy available. Training should include all three of these key components. Whether or not doing so will always prevent injury remains to be seen.