Key Points:

A recently published scientific study attempts to explain why puberty leads to an increased risk in ACL tears for girls and boys but tends to affect girls more
An increased Body Mass Index is a risk factor for ACL tear regardless of age or sex
The results suggest that ACL tear prevention programs should start before puberty in girls

This blog is focused on providing a sports medicine physician?s perspective on issues affecting youth sports health and participation. Our fundamental belief is that youth sports done right has numerous benefits, which can lead to a lifetime of good health habits. But as an orthopedic surgeon I?m often troubled by the younger ages at which we see some types of injuries, and the younger ages at which surgical care is done for these injuries. Two particularly bothersome areas are ACL tears in the knee and Ulnar Collateral Ligament tears in the elbow.

Let?s take a look at ACL tears in athletes as young as age nine. A recent publication by Stracciolini and colleagues sheds light on the pediatric ACL problem in very young athletes. Their study shows that boys appear to injure more ACLs before puberty while girls catch up later through their teenage years. The study also shows that higher Body Mass Index (BMI) is associated with a higher risk of ACL tears, regardless of age and sex. Why BMI is independently associated with ACL injury is puzzling. Could it be that the immature neuromuscular system is not yet capable of absorbing the added forces produced by an increased BMI? There are implications for improving the young athlete?s health from each of the points raised in the paper.

First, this study shows that ACL injuries make up a higher proportion of the total number of sports injuries as kids move through puberty. This is especially true for girls and is in line with other studies showing that girls have a higher injury ratio than boys starting at around age 12. In contrast to boys, girls may have greater generalized joint looseness after the onset of puberty, and it seems that the joint looseness is a risk factor for ACL tear. There is also some evidence that changes in the hormones estrogen and progesterone associated with the menstrual cycle are risk factors for girls.

Second, the authors also showed data that supports an association between higher Body Mass Index and the risk of an ACL tear. This risk was present regardless of age and sex. In other words, at any age, if two young athletes are compared and one has a ?normal? BMI for age and the other has an elevated BMI, the athlete with the elevated BMI has higher risk for tearing an ACL.

There are many factors involved in the exact process of ACL tears but the authors attempt to tie everything together like this: After the onset of puberty and a rapid growth spurt, there is increased bone length and increased overall body mass. This leads to increased height of the center of mass and decreased core stability. Poor core stability places the ACL at risk.

Wow, that was a lot to digest in a small amount of space. The practical implications are these: puberty results in a significant increased risk for ACL tears in girls, and an increased BMI increases ACL tear risk in boys and girls regardless of age. One strategy for girls would be to introduce school or team ACL injury prevention protocols before puberty. This has the potential to reduce ACL tear risk into puberty and later years. Start saving your ACL as early as possible!

By Dev Mishra, M.D.,?President, Sideline Sports Doc,?Clinical Assistant Professor of Orthopedic Surgery, Stanford University