July 15 (UPI) -- Young athletes who sustain an ACL injury are at increased risk for a second knee injury when they return to sports, according to research.
Researchers found that patients who failed to achieve 90 percent quadricep strength on a battery of tests were 84 percent less likely to sustain an ipsilateral graft failure but three times more likely to suffer a contralateral anterior cruciate ligament, or ACL, injury.
ACL injury affects as many as 250,000 individuals in the United States annually, resulting in an annual health care cost exceeding $2 billion, according to the Centers for Disease Control and Prevention. The incidence of ACL injury is greater in males due to greater exposure to physical activity, but the relative risk of injury per exposure is two to eight times greater in females, the CDC found.
The researchers followed 181 female athletes, all average age of 16, for two years following an ACL injury.
"Current criteria to evaluate readiness to return young athletes to pivoting and cutting sports, may not identify young, active patients independently at high risk for a future ipsilateral graft tear or contralateral ACL injury," researchers wrote in the study, which was led by the Dr. Mark V. Paterno, of Cincinnati Children's Hospital Division of Sports Medicine. "Inability to achieve 90 percent LSI on an isometric quadriceps strength assessment resulted in a reduced risk of ipsilateral graft failure, but an increased risk in contralateral ACL injury after ACL reconstruction and current return to sport."
The study was presented at the Annual Meeting of the American Orthopedic Society of Sports Medicine, held July 11-14 in Boston.
Orthopedic surgeons and sports medicine professionals have relied on the return-to-sports criteria to help guide patients as they consider participating in athletic competition after injury.
The strength of the quadricep is viewed as one of the most important measures to predict risk for further injury to the ACL.
In the return-to-sport assessment, athletes underwent isometric quadriceps strength, four functional hop tests and the International Knee Documentation Committee patient reported outcome survey.
Athletes were classified as those who successfully passed all six return-to-sport tests at a level of 90 percent compared to those that failed to meet all six criteria. Limb symmetry index was calculated for strength and hop test assessments.
Fifty-seven patients achieved 90 percent or greater on all testing.
The researchers wanted to know if passing all six measures resulted in a reduced risk of second ACL injury in the first 24 months after returning to their sport. They also wanted to assess if the ability to successfully pass individual return-to-sport criteria resulted in reduced risk of a second ACL injury.
Of the 181 patients enrolled, 39 sustained a second ACL injury, including 18 ipsilateral graft failures and 21 contralateral ACL tears in the first 24 months.
There was also no difference in contralateral ACL injuries between patients who passed all criteria -- 7 percent -- and those who failed at least one criterion, at 13.7 percent.
"Further investigation is needed on the relationship between quad strength and side of future ACL injury and whether other factors may help contribute to a predictive model of future ACL injury specific to limb," Paterno said.