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I'm the coach for a girls' high school basketball. As we get ready for the next season, what's the latest on these ACL injuries girls seem susceptible to?

Just as you already know, it's clear that knee injuries are problematic for female athletes. In particular, anterior cruciate ligament (ACL) tears are common. Rehab and recovery from such an injury can put a player on the bench for an entire season. Scientists at human movement and biomechanic research laboratories continue to study this problem. They start with cadavers (knees preserved after death for study) and examine the effect of load, torque, and alignment on movement of the knee. Then they study the spring, laxity, and stiffness qualities of human male versus female knees under different conditions. They know that there are differences in alignment. These are important factors. But they also know that there's a sex-difference in how stiff the joint is. This kind of stiffness isn't what we refer to as we get older. This quality is the response of the joint to loads, especially twisting or side-to-side force. The muscles around the knee tighten up to prevent joint displacement and thereby prevent ligament damage. Men seem to have a stable level of stiffness. No matter how much load is applied (small to large), the joint doesn't give. But women seem to have variable stiffness. Low loads respond with less stiffness than higher loads. This is okay when the load increases gradually. But it becomes a problem when there's a sudden shift in load. The knee stiffness doesn't increase quickly enough to prevent injury. How to respond to this in practice remains to be seen. As more information about differences between male and female athletes is collected, practical suggestions may be easier to make.

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