A torn anterior cruciate ligament, or ACL, is a sports injury that you hear about all the time.  Young female athletes are seven times more likely to have this injury than boys.  In fact, some sports medicine doctors say the rise in ACL injuries among girls is an "epidemic."

  Casey Arnold is a 14-year-old soccer player, traveling the country competing.  Last May, she took a serious hit that sidelined her.

  "My leg locked and my goalie came out and smashed it in," said Casey.

  It turns out she tore her ACL.

  "ACL tears are an epidemic in the young, female athletes.  It's probably seven times as common to have an ACL torn in a female as it is in a male," said Dr. Stephanie Martin, a pediatric orthopedic surgeon.

  And it happens in all age groups.

  “If you play a varsity sport, let's say soccer or basketball in high school, one in 100 girls will tear their ACL.  If you play varsity basketball or soccer in college, one in 10 will tear their ACL," said Martin.

  The reason that girls are so vulnerable has to do with hormones and looser ligaments.  There’s also another reason.

  "It has to do with the fact that their pelvis is over their knees, over their feet; (that makes them) a little bit more knocked-kneed.  When they land jumps, they tend to land stiffer kneed," said Martin.

  Studies have shown a torn ACL puts their body at risk at a later age, too.

  "They do have increased risk down the road for arthritis," said Martin.

  Casey had reconstructive surgery and is going through physical therapy to prevent future injuries.

  "It's a lot stronger.  Surprisingly, my bad leg is better than my good leg now," she said.

  She's anxiously awaiting her turn back on the field.