For some young people who experience an ACL (anterior cruciate ligament) injury, delaying surgical repair is associated with a higher risk of new tears in the meniscus and cartilage after the initial injury. That’s according to a new study by Johns Hopkins Children’s Center researchers, who found that adults with the same type of so-called ACL injury generally showed no significant increase in such risk.

The likely explanation? Adults are more likely to dial back physical activity and comply with calls for restrictions from a doctor, while children are more likely to continue strenuous sports and other play, and experience further knee damage that may not at first be obvious.

“What we have shown with children is that the longer you wait, the more damage may be done to the knee,” says R. Jay Lee, senior author of the study and a pediatric sports medicine specialist at the Children’s Center.

In the study, which appeared in the Orthopaedic Journal of Sports Medicine, the Johns Hopkins investigators worked to establish the risk of tears to the meniscus, a C-shaped pad of cartilage in the knee, in pediatric and adult patients. They did so by comparing the presence of new meniscal tears discovered during arthroscopy with tears present during an MRI taken around the time of an initial ACL injury.

The researchers say the findings reinforce the need for timely surgical treatment in pediatric patients to prevent ongoing damage to the knee.

ACL tears, often experienced as a “popping” sensation in the knee, are especially common in children and adults who play sports that involve sudden, sharp changes in direction, such as football, soccer, lacrosse and basketball. Research estimates that between 100,000 and 200,000 people each year tear their ACL in the United States. Historically, physicians have recommended that ACL reconstruction be delayed in younger patients until the child is finished growing. However, in people of all ages, ACL tears leave the knee unstable and more prone to further injury.

The researchers say they hope their findings will help inform decisions when adults and caregivers of children who experience ACL injuries are deciding when to have surgery. The researchers will continue their investigation, particularly looking at whether restricting patients’ mobility has an effect on new meniscal tears.