ACL injury is at the top of the list when it comes to sport-related injuries. Within this year’s football season alone, the number of college and professional athletes reporting that they have or suspect an ACL injury continues to grow. Observers may assume this common injury is due to the high-impact play, but researchers are now pointing to another important factor.
Measurements of the ACL were calculated through magnetic resonance imaging (MRIs) of the knee. Researchers found that participants who have previously injured their ACL had an average ligament size ten percent smaller than participants of similar size who had not injured their knee.
When measuring the ACL size in participants with former injuries, investigators used the opposite, uninjured knee. The injuries suffered by these participants were noncontact injuries.
This study consisted of 54 participants, who were divided into two groups. Those with previous injuries were paired with uninjured participants of the same age, gender, height and weight.
Signs of an ACL Tear
You may experience:
Falling to the ground
Pain in the knee
Immediate onset of swelling
Instability of the knee—a feeling of looseness within it or that it can't be "trusted"
"If you compared two people of the same weight, based on our data set, we would expect the injured person had the smaller ACL," said Ajit Chaudhari, assistant professor of orthopedics at Ohio State University and lead author of the study.
Researchers, with the aid of an orthopedic surgeon experienced in operating on injured knees, used the MRIs to determine the outline of each ACL.
Results showed that 16 of the 27 injured participants had smaller ACLs than their matched controls. Overall, the injured group had an average ACL volume of 1,921 cubic millimeters, while the control group had an average volume of 2,151 cubic millimeters.
Based on what is currently known about the fibrous design of the ligament, researchers believe that a smaller ACL is more prone to injury.
"If you have a weaker ACL, it's more likely to tear if all other factors are equal," said Chaudhari. "If being larger in size means the ACL has more fibers, then that would make it stronger. If the individual building blocks are of similar strength, then it comes down to how much total tissue there is."
While this study provides evidence of a connection between ACL size and injury, the use of MRIs are not suggested by researchers as a way to screen potential athletes, due to the expense of the testing and an uncertainty of how individuals will react to physical activity.
"I would certainly not say in any way, shape or form that people should start using ACL size as a determinant of whether they should play any sport," Chaudhari said.
By incorporating the proper training techniques, athletes can reduce their risk of ACL injuries. It is important to perform training drills that require balance, power and agility, such as plyometric exercises. Plyometrics is a type of exercise training designed to produce fast, powerful movements in which a muscle is loaded and then contracted in rapid sequence, using the strength, elasticity and innervations of muscle and surrounding tissues.