Review Question - QID 8921

Different neuromuscular recruitment patterns (high quadriceps-to-hamstring activity ratio) and landing/cutting biomechanics (decreased hip and knee flexion, increased knee external rotation with subsequent dynamic knee valgus) contribute most to the increased incidence of anterior cruciate ligament (ACL) tears in female athletes.

ACL tears are 2-9 times more common in female athletes compared to their male counterparts. This difference in ACL injury rates is not seen until puberty. A variety of factors are postulated to play a role in this discrepancy, including smaller femoral notch size, smaller ACL, increased Q angle and hormonal differences. Altered neuromuscular activation and movement coordination appear to be the most important reason for different ACL injury rates between the sexes. ACL prevention programs primarily aim to modify these maladaptive neuromuscular and biomechanical patterns.

Griffin et al. summarized the findings of the second Hunt Valley Meeting, focusing on risk factors for ACL injury and current prevention programs. There is good evidence that neuromuscular training, including strengthening and flexibility exercises, plyometrics, agility and technique training, as well as a heightened awareness of the biomechanics of injury, reduces ACL injury risk in female athletes. Randomized trials are underway to determine the longitudinal effect of initiating prevention programs at an early age. The impact of ACL prevention programs is still largely unknown.

Voskanian et al. reviewed risk factors for ACL injury in female athletes and proposed key elements for a successful ACL prevention program. The authors recommend initiation of the prevention program prior to puberty, incorporation of neuromuscular training and muscle strengthening, as well as education and feedback regarding body mechanics and proper landing patterns. Strengthening should focus on the hamstrings and hip abductors, which may decrease dynamic knee valgus. Lastly, the program should be easy to follow, and require minimal equipment and time commitment, so as to enhance compliance.

Zebis et al. evaluated the effects of implementing a prophylactic neuromuscular training program in female athletes. Neuromuscular activity of the lower extremity was analyzed with electromyography (EMG) during performance of a side-cutting maneuver in 12 soccer players and 8 handball players, before and after implementation of a neuromuscular training program. Neuromuscular training increased the pre-landing and landing EMG activity for the medial HS muscles, while the quadriceps EMG activity remained unchanged. An increased ratio between HS and quadriceps activity may decrease the risk of dynamic knee valgus and subsequent ACL tear.

Illustration A is a comprehensive injury causation model from Griffin et al. that details the various risk factors that may contribute to an ACL tear.

Incorrect Responses:
Answer 1: High quadriceps-to-hamstring activity ratio is associated with increased risk of ACL injury, not high hamstring-to-quadriceps activity ratio. Aggressive quadriceps loading of the knee has been found in cadaveric studies to result in significant anterior translation of the tibia relative to the femur, and hence it has been proposed as a potential mechanism of injury.
Answers 3 + 4: While the association between elevated estrogen and ACL injury has been suggested, there is no scientific consensus that hormonal variations in different stages of the menstrual cycle play a role in higher incidence of ACL injury in females, though research in this area is ongoing.
Answer 5: Females do have smaller femoral notches compared to males, but this anatomic factor is far less significant than neuromuscular coordination.