Preventing ACL Injury

Anterior Cruciate Ligament (ACL) tears are one of the most common knee injuries suffered by athletes, but they are significantly more prevalent in young, female athletes. I would know…I have torn both of mine. As an NCAA Division I volleyball player, I worked my way up the ranks from playing in high school, at the club level, and even at a junior college. Never once was I screened for deficits that could lead to a catastrophic injury like an ACL tear. Maybe if I had, I would not have needed 5 knee surgeries total, including two ACL reconstructions.

The ACL attaches from the posterior (back) of the femur (thigh bone) to the anterior (front) tibia (shin bone) and its main purpose is to limit anterior translation (forward gliding) of the tibia. It also helps to limit excessive internal and external rotation (turning) of the tibia. Thus, the main mechanism of injury for an ACL tear is hyperextension of the knee causing anterior translation of the tibia combined with a rotational force…often seen when an athlete plants their foot and pivots simultaneously.

Why do young female athletes suffer ACL injuries four to six times more often than their male counterparts? There is a biomechanical angle measured through the hip and knee called the “q-angle” that shows the relationship between the hip and knee. Females have a larger q-angle because we tend to have a wider pelvis than males. The wider pelvis causes a more valgus orientation of the knee (see the picture below). That valgus orientation puts significant pressure on the medial (inside) of the knee and ultimately changes the biomechanical efficiency of the knee joint itself. The increased valgus forces put excess pressure on the stabilizing ligaments in the knee, like the ACL, and increase the natural rotation of the knee. There is evidence that a lack of core stabilization also contributes to ACL injuries. Decreases in core neuromuscular control can increase uncontrolled truck displacement which leads to higher knee ligament strain and ACL injury.

A good way to identify athletes at risk of an ACL injury is to do a screening test, such as the Tuck Jump test. This test requires the athlete to complete repetitive tuck jumps (jumping while tucking the knees toward the body) over the course of 10 seconds and the person screening should look for the athlete’s tendency to land with their knees in a valgus orientation which identifies a neuromuscular imbalance that needs to be addressed.

The increased valgus orientation of the knees is often caused by the increased firing of the quadriceps and decreased activation of the gluteal muscles. A great way to reactivate the glutes is to perform the exercise below.

Hip Bridge with Resistance Band:

Begin by lying on the floor with knees bent and feet flat on the floor. Place a resistance band around the thighs just above the knees. Slightly abduct the legs (separate the knees) while simultaneously performing a hip bridge (bringing the hips off the ground). Slowly lower to start position without bringing the knees together. Perform 3 sets of 10 repetitions.

Valgus collapse of the knee can also be contributed to weak hip abductors and external rotators, like the gluteus medius. Performing the clamshell exercise will help strengthen those muscles.

Clam Shell with Resistance Band: