The Athletic Knee, Part I.

You’re out playing a soccer game, a tennis match, or maybe even down hill skiing when all of a sudden you lose your balance and feel a “pop” in your knee. For a moment, the pain is excruciating, but then it becomes more tolerable. However, your knee starts to swell and it is painful to walk on. So, you are helped off the field, court, or get a sled ride down the mountain. Unfortunately, you have just joined the nearly 200,000 others who will tear their Anterior Cruciate Ligament (ACL) this year.

With a general increase in organized sports and year round training, games and tournaments, it is not surprising that the exposures and risks for ACL injuries has increased as well. If you are female athlete (especially those participating in soccer, basketball or gymnastics) your risk of injuring your ACL is 2 – 10 times greater than your male counterparts, and the numbers are growing! With the advent of Title IX legislation and the rise in opportunities for female athletic participation, a whole new number of athletes have become at risk of injury.

ANATOMY
The ACL is one of the four principle ligaments which help to stabilize the knee. The ACL is anterior or in front of the Posterior Cruciate Ligament (PCL) and crosses it from inside to outside. The other two major ligaments are the Medial Collateral Ligament (MCL) on the inside part of the knee, and the Lateral Collateral Ligament (LCL) on the outside part of the knee. The ACL functions to prevent the Tibia (shin bone) from being pulled off the Femur (thigh bone). The quadriceps (thigh) muscles in front help to extend the knee and the Hamstring muscles in back help to flex or bend the knee. The hamstrings are vital as they actively help to prevent the quads from pulling the tibia off the femur.

RISKS
The probability of tearing your ACL is increased if you are involved in a contact or collision sport that includes cutting, twisting and jumping. However, it is important to note that non-contact ACL injuries (where no one hits you) are responsible for 70% of these injuries, where direct contact accounts for only 30%. Again, female athletes have an increased incidence of non-contact ACL injuries than do male athletes (up to 10%).

GENDER DIFFERENCES
Some of the factors increasing the risk of injury to the female athlete include:

Anatomical Structure: women tend to have wider pelvises than men and tend to be more “knock-kneed”, putting increased stresses across the knee joint.
Muscular Activation: female athletes do not contract the hamstrings as quickly as male athletes and are unable to protect the ACL from shearing forces.
Ligament Structure: the female ACL is smaller in diameter than the corresponding male ACL.
Hormonal Differences: Some have even suggested a hormonal reason, however this remains relatively inconclusive.

Coming in The Athletic Knee, Part II, we will discuss the methods used to reduce the liklihood of non-contact ACL injuries to the knee….