Decreasing Knee Injury Risk Factors With Neuromuscular Training

Injury Background Anterior cruciate ligament (ACL) tears are disabling injuries that place a significant burden on the athlete. The average cost for ACL reconstruction is estimated to be approximately $17,000 per patient and full recovery commonly takes around 6 months to achieve. It has been estimated that 1 in every 3000 people in the United States suffer an ACL rupture each year. Roughly 80% of these injuries are linked to a noncontact mechanism, with more than 70% of them occurring while landing from a jump.

Injury Mechanism Upon landing, the lower body falls into what is referred to as the "position-of-no-return" (PNR). The landing kinematics involved with the PNR places a high amount of stress on the ACL and can ultimately lead to a complete rupture.

Injury Imbalance Female athletes who participate in sports that involve jumping and cutting activities suffer 4-to-6 times more ACL injuries than males who participate in the same sports. This is attributed to the higher number of risk factors that females possess during and after puberty. In particular, upon maturation, males exhibit a neuromuscular spurt, with increases in power, strength, and coordination, whereas females do not. Other risk factors that females demonstrate are quadriceps dominance and ligament dominance. Both of these dominances are linked to the landing kinematics of the knee when placed in the PNR.

Quadriceps dominance is characterized by the extended knee posture that is displayed in the PNR when landing from a jump. When landing on an extended knee, the tibia is translated anteriorly to the femur, causing the ACL to become taunt. In order to prevent the ACL from rupturing, the hamstrings must activate to flex the knee and translate the tibia posteriorly. In response to anterior tibial translation, females are found to utilize a different muscle recruitment pattern than males by contracting their quadriceps before their hamstrings, whereas males follow the opposite pattern. By contracting the quadriceps first, the hamstrings are overpowered, which allows for further anterior tibial translation to occur during landing.

Ligament dominance is evidenced by the increased knee valgus that displayed in the PNR when landing and cutting. During these maneuvers, females rely on their knee ligaments rather than lower extremity musculature to absorb ground reaction forces. This tendency places a high amount of stress on the ACL, which in turn, increases the probability of it rupturing.

Injury Prevention Due to the high rate of noncontact ACL injuries seen in female athletes, neuromuscular training (NMT) programs have been developed in an attempt to prevent or reduce the risk of injury. These programs are administered as either an off-season regimen or in-season warm-up routine, and they incorporate a combination of plyometric, proprioceptive, and strength training exercises, with particular focus being placed on correct technique. By modifying neuromuscular risk factors, NMT programs have been able to significantly reduce the rate of noncontact ACL injury.

Specific Aim 1:

To evaluate the effectiveness that an ACL prevention program has on modifying at-risk landing mechanics (associated with noncontact ACL injury) compared to a resistance training program of equal workload.

Specific Aim 2:

To evaluate the effectiveness that an ACL prevention program has on improving max vertical jump height compared to a resistance training program of equal workload.