An ACL injury is a common type of knee injury in athletes.
"Even though additional research still needs to be performed to support our findings, our data does provide early evidence for re-examining current rehabilitation and return-to-sport protocols following [ACL reconstruction]," said study author Mark Paterno, of Cincinnati Children's Hospital.
The study included 59 females and 19 males, aged 10 to 25, who underwent ACL reconstruction and returned to sports, and a control group of 47 people who had never suffered an ACL injury.
After two years, 23 of those in the reconstruction group and four of the people in the control group had suffered an ACL injury. Overall, 29.5 percent of athletes suffered a second ACL injury within two years of returning to sports, with 9 percent re-injuring the same knee and 20.5 percent suffering an injury to the opposite knee.
Within the ACL reconstruction group, females were twice as likely as males to suffer an injury to the opposite knee, according to the study.
The findings are scheduled for presentation Thursday at the annual meeting of the American Orthopaedic Society for Sports Medicine in Chicago.
"In our study, female athletes after [ACL reconstruction] demonstrated more than four times greater rate of injury within 24 months than their healthy counterparts," Paterno said in a society news release.
The data highlights the fact that after ACL reconstruction, patients who return to playing sports are at greater risk for injury and should take appropriate precautions, he added.
Data and conclusions presented at meetings should be considered preliminary until published in a peer-reviewed medical journal.
The MedlinePlus Medical Encyclopedia has more about ACL injury.