Sports-related knee injuries in children and adolescents are increasing at “an alarming rate,” U.S. researchers said.

Doctors at the Children's Hospital of Philadelphia noted an increase of more than 400 percent in these types of injuries at their institution over the last decade.

From 1999 to 2011, ACL tears have increased by 11.35 injuries per year, meniscus tears have increased by 13.95 injuries per year and tibial spine fractures have increased by 1.07 injuries per year, according to hospital billing records of patients under age 18.

While the exact cause of the growth in knee injuries is unclear, the researchers said increased diagnosis, earlier referral and more aggressive treatment may partly account for the rising numbers.

In addition, "the high-level, year-round, young-age specialized sports competition has been cited as one cause for the increase," said lead study author Dr. Todd Lawrence.

"The implications of ACL tears and meniscus tears in children and adolescents are significantly greater than the same injuries in adults," Lawrence added.

Reconstruction procedures can be complex, requiring lengthy recovery, and can also potentially impair growth. Returning to high-level sports after healing can also place young athletes at high risk of re-injury.

"While we are never going to prevent all injuries, there is good evidence, particularly for some sports like soccer, that sports injury prevention programs can go a long way towards reducing them," Lawrence said.