ACL Injury Prevention
The anterior cruciate ligament crosses from the medial surface of the tibia to the lateral condyle of the femur. Its primary function is to prevent anterior translation of the tibia and has a secondary role in preventing internal or medial rotation of the knee.
Participation in activities that require multidirectional movements such as pivoting, cutting, and quick deceleration, as well as loading activities, place athletes at a higher risk for injury. These activities require a higher level of lower extremity strength, stability and muscle balance to prevent the excessive anterior and medial forces at the knee that place the ACL under heavy strain. Deficits in any of these areas place the athlete at a higher risk for an ACL injury, taking him or her out of their sport and into a lengthy rehabilitation process.
The following are evidence-based risk factors for non-contact ACL tears (3):
Some of these risk factors are inherent and cannot be changed, like being female, having laxity in your joints, and anatomical characteristics in bone structure. However, issues with loading pattern, muscle recruitment and strength imbalance can be addressed and corrected in order to decrease an athlete’s risk for an ACL tear.
The amortization phase of jumping is the short time between loading to prepare for a jump and actually jumping. With sufficient strength and muscle balance, the knee will maintain a neutral position during this phase, resulting in an explosive plyometric movement and adequate loading for landing. However, multiple factors affect this pattern and place the knee in a faulty posture, setting up risk for a multitude of knee injuries, ACL tears included.
When the knee falls medial to the line between the hip and foot, a large valgus load is placed on the joint. The term “knee valgus” refers to the knee falling inward, or in a knocked-knee position. This dynamic valgus force places the tibia into internal rotation.
In addition, if an athlete is quadriceps dominant, meaning they do not have sufficient hamstring co-contraction to counteract the anterior force the quad places on the tibia, the tibia undergoes very quick anterior translation along with the medial rotation from the valgus load. These motions are the exact movements the ACL helps to prevent. The ACL simply cannot withstand the force of landing in that position, and a sprain or tear will occur.
Women are anywhere from 2.4 to 9.7 times more likely to sustain an ACL injury than men across multiple sports (5,6). This increased risk is not only due to a wider pelvic structure and hormone cycles that causes joint laxity, both of which are fixed and unalterable, but women have also been shown to demonstrate more quadriceps dominance during plyometric activity when compared to men. Women generally have less hamstring and glute activation when compared to their male counterparts during loading and landing, making them more likely to sustain a non-contact ACL injury.
Improving lower extremity muscle recruitment and strength can improve the forces placed on the ACL during these high level activities. A consultation with a trained physical therapist can help to identify which of these risk factors an athlete may present. PTs are trained to not only identify these biomechanical errors, but to design a strengthening and muscular re-education program specific to the athlete’s sport or activity. Identifying and correcting these movement patterns is not only important in the prevention of knee injuries, but as part of the rehabilitation process after ACL reconstruction.
At Austin Sports Medicine and its Center for ACL Injuries, identifying risk factors and addressing mechanical issues in an attempt to prevent knee injuries is a priority. However, most patients present for treatment once an injury has occurred. ACL injury prevention is part of ASM’s routine rehabilitation protocol, even after reconstructive surgery, with the goal being to return an athlete back to his or her sport with less likelihood to re-tear and be taken away from their sport or activity again.