• Hip & Knee Conditions
• Sports Medicine

• Orthopaedics
• Hip & Knee Conditions
• Sports Medicine

Anterior cruciate ligament (ACL) injuries in athletes are common, especially among females, who are at a 2- to 10-times greater risk than males. The causes are multifactorial but can be avoided with proper training. Timothy E. Hewett, PhD, The Ohio State University Medical Center, Columbus, Ohio, USA, discussed the mechanics of ACL injuries in terms of neuromuscular, anatomical, biomechanical, hormonal, and growth and development risk factors. The study of these form the groundwork for a prevention program developed at The Ohio State University Medical Center.

Female athletes have a greater risk of ACL because of increased dynamic valgus and high abduction loads during landing. Other biomechanical and neuromuscular risk factors identified include dynamic trunk instability, proprioception, history of low back pain, and greater knee joint laxity [Myer GD et al. Am J Sports Med 2008; Zazulak BT et al. Am J Sports Med 2007; Hewett TE et al. Am J Sports Med 2005].

For those at high risk for a first ACL rupture, studies have shown a body-knee connection to injury where there is uncontrolled trunk or core motion coupled with knee abduction. To make female athletes less vulnerable to ACL tear, Dr. Hewett recommended training that addresses the mechanisms leading to knee abduction: not allowing the knee to cave in and training to increase hamstring and quadriceps recruitment, single-leg balance and symmetry, and dynamic core stability. This training identifies the neuromuscular imbalances—ligament, quadriceps, leg, and trunk dominance—that make the knee vulnerable to ACL injury.

Females diverge in ACL injury rates from males at ∼ 12 years, the time that the majority of females begin puberty. ACL injuries peak in females at age 16. During females' adolescent growth spurt, their landing motion patterns are considerably different from those of males. Female athletes display greater total medial motion of the knees and a greater maximum lower extremity valgus angle than do male athletes on landing. Flexor torque decreases, and there is an increase in dynamic valgus angulation of the knees after maturation [Hewett TE et al. J Bone Joint Surg Am 2004].

In a study that examined longitudinal risk factors of ACL in females during maturity, incremental increases in height, body mass index, and anterior knee laxity were associated with decreased hip abduction and knee flexor strength and increased knee abduction loads after each year of growth. These changes increased the risk of ACL injury [Myer DG et al. J Athl Train 2009]. In females, increased body mass and height of the center of mass, without matching increases in hip and knee strength, may underlie increased knee abduction loads. Peak height velocity and high load coincide in females but not males.

Combined biomechanical and epidemiologic studies and video analysis provide evidence that sex-specific mechanisms of ACL injury may occur, with women sustaining injuries by a predominantly valgus collapse mechanism. ACL injury preventive programs should focus on the reduction of high-risk valgus, the reduction of loads, and the stability of sagittal-plane movements.

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