If you have ever been around sports, whether it was youth, scholastic, intramural, college, professional, or rec league, you probably know someone who has had an anterior cruciate ligament (ACL) injury. You may have even experienced an ACL injury yourself. The ACL is a ligament inside the knee between the femur (thigh bone) and tibia (shin bone). Its primary function is to provide stability to the knee by limiting the forward movement of the tibia and internal rotation of the knee. According to the CDC, there are an estimated 250,000 ACL injuries per year in the United States. The majority of injuries happen during physical activities that require rapid deceleration and change of direction. There is no way to prevent ACL injuries, but measures can be taken to reduce some of the risk factors that contribute to injury.
Some of the risk factors associated with ACL injuries include gender, ankle/hip mobility and stability, lumbopelvic stability, hamstring strength, and body composition.
Gender: Although significantly more males suffer ACL injuries each year compared to females, females are 2-8x more likely to have knee injuries if involved in sports or physical activity due to the differences in skeletal structure. Females have proportionally wider pelvises than males, which can cause knee valgus (caving in) and over pronation of the feet (flattening of the arches). Females need to place extra emphasis on minimizing the other risk factors mentioned below.
Ankle/Hip Mobility and Stability: The ankle and hip joints have a wide range of motion, while the knee is simply a hinge joint. If range of motion is restricted in the ankle and hip, it causes more torsion at the knee joint. Vice versa, torsion of the knee happens if the ankle and hip joint are unable to stabilize under stress. It is critical to maintain a full range of motion at the ankle and hip, while at the same time possessing the ability to maintain integrity of movement while under stress.
Lumbopelvic Stability: The strength, stability, and endurance of the body’s midsection (abs, obliques, glutes, lower back) dictates how efficiently force is produced and resisted. The midsection is the essential link between the upper and lower body. If the midsection cannot effectively handle the repeated stress of physical activity, it will negatively affect gross motor control. This causes a complete breakdown in function throughout the entire kinetic chain. Research has shown a strong correlation between poor motor control and/or fatigue contributing to ACL injuries.
Hamstring Strength: Stopping, changing direction, and landing all require an eccentric contraction (resisting force) of the quadriceps, hamstrings, glutes, and calves. In most people, there is a discrepancy between how strong the quadriceps are compared to the hamstrings. The tibia can slide forward too far if the hamstring cannot eccentrically resist force during deceleration, putting tremendous force on the anterior cruciate ligament.
Body Composition: As was stated earlier, most ACL injuries occur during rapid deceleration and change of direction. Maintaining a healthy body composition simply means there is less mass to slow down and redirect. Think of lean muscle mass as the braking system for the body. It is important to have sound brakes and a manageable load to stop when it comes to performance and reducing the risk of injury.
The best way to reduce the risk of ACL injuries, and other orthopedic injuries, is to engage in a comprehensive exercise program that includes functional resistance training, agility and plyometric drills, balance and coordination training, and mobility. I will discuss all of these at length in part two of this blog series. Thanks for reading!
One Body! One Life! CARE for It!