The England scrum-half has damaged his anterior cruciate ligament (ACL), which could mean six months on the sidelines.

BBC: Ellis faces World Cup heartache

Anterior cruciate ligament (ACL) injuries are very common in young athletes, especially in women because of structural differences in their bodies, which tend to begin when they reach puberty.

CNN: How do I protect my daughters' knees from sports injuries?

The screening techniques are so accurate that the National Basketball Association has asked OSU doctors to help identify which of their athletes are at the highest risk for anterior cruciate ligament, or ACL, and other injuries, and to come up with programs to try and prevent them, so that more players are on the court than on the bench.

CNN: Keeping the world's Kevin Wares injury-free