"The Uneven Playing Field", by Michael Sokolove, The New York Times, 11 May 2008
This article mainly focuses on ACL injuries among high-school age girls, which are roughly
five times more prevalent than among boys playing the same sports at the same age. A team of 18 girls playing a typical schedule of soccer games can expect one season-ending ACL injury to a player every year. One team cited in the article had 6 players in varying stages of recovery from ACL injuries, two of whom had had surgery on both knees. The article also notes that concussions are roughly 1.5x more prevalent among teenaged girls than teenaged boys (high school girls playing soccer suffer concussions at the same rate as high school boys playing American football).
One possible reason for the discrepancy is the growth hormones during adolescence, when boys get more testosterone and girls get more estrogen. Of course, prior to adolescence, boys and girls are much more the same. Interestingly, testosterone typically causes a reduction in flexibility as it increases strength, so teenaged girls might actually have an edge over boys in jiu-jitsu.
Things that make you go "ew...": Apparently, an ACL doesn't really
tear, so much as it explodes and dissolves into a puddle of worthless goo, no longer connecting your thigh to your lower leg...