Abstract: High school and collegiate female athletes have a significantly increased risk of sustaining a noncontact anterior cruciate ligament injury compared with male athletes participating in the same sport. This review summarizes the current knowledge of the risk factors hypothesized to influence this problem, and the neuromuscular training programs designed to correct certain biomechanics problems noted in female athletes. The risk factors include a genetic predisposition for sustaining a knee ligament injury, environmental factors, anatomical indices, hormonal influences, and neuromuscular factors. The greatest amount of research in this area has studied differences between female and male athletes in movement patterns during athletic tasks; muscle strength, activation, and recruitment patterns; and knee joint stiffness under controlled, preplanned, and reactive conditions in the laboratory. Neuromuscular retraining programs have been developed in an attempt to reduce these differences. The successful programs teach athletes to control the upper body, trunk, and lower body position; lower the center of gravity by increasing hip and knee flexion during activities; and develop muscular strength and techniques to land with decreased ground reaction forces. In addition, athletes are taught to preposition the body and lower extremity prior to initial ground contact to obtain the position of greatest knee joint stability and stiffness. Two published programs have significantly reduced the incidence of noncontact anterior cruciate ligament injuries in female athletes participating in basketball, soccer, and volleyball. Other programs were ineffective, had a poor study design, or had an insufficient number of participants, which precluded a true reduction in the risk of this injury. In order to determine which risk factors for non contact anterior cruciate ligament ruptures are significant, future investigations should include larger cohorts of athletes in multiple sports, analyze factors from all of the major risk categories, and follow athletes for at least one full athletic season. Future risk assessment studies should incorporate reactive tasks under more realistic sports conditions.
Background: Although neuromuscular indices have been extensively studied in adolescents and adults, limited data exist for prepubescent children.
Hypothesis: No differences exist between prepubescent boys and girls in lower limb strength, symmetry on single-legged hop testing, and limb alignment during drop-jump testing.
Study Design: Cross-sectional study (prevalence); Level of evidence, 1.
Methods: The authors tested 27 female and 25 male athletes who were aged 9 to 10 years and matched for both body mass index and years of organized sports participation. In a drop-jump screening test, the distance between the right and left hips, knees, and ankles was measured as an indicator of lower limb axial alignment in the coronal plane. The distance between the knees and ankles was normalized by the hip separation distance. Quadriceps and hamstrings strengths were measured isokinetically at 180 deg/s. Lower limb symmetry was determined from 2 single-legged hop function tests.
Results: Boys demonstrated greater mean absolute and normalized knee and ankle separation distances on the drop-jump test. Even so, 76% of boys had a normalized knee separation distance of 60% or less of the hip separation distance, as did 93% of girls, indicating a distinctly valgus alignment. There were no differences between the sexes in quadriceps and hamstrings peak torques, hamstrings/quadriceps ratio, time to peak torque, total work, or lower limb symmetry values.
Conclusions: A high percentage of the prepubescent athletes studied had a distinctly valgus lower limb alignment during the drop-jump test and a lack of lower limb symmetry during the hop tests. These same indices have been hypothesized to increase the risk for knee ligament injuries in older athletes. Neuromuscular training may be needed to address these issues in children.
Abstract: While many anterior cruciate ligament (ACL) prevention programs have been
published, few have achieved significant reductions in injury rates and improvements in
athletic performance indices; both of which may increase compliance and motivation of
athletes to participate. A supervised neuromuscular retraining program (18 sessions) was
developed, aimed at achieving both of these objectives. The changes in neuromuscular indices
were measured after training in 1000 female athletes aged 13–18 years, and the noncontact
ACL injury rate in 700 of these trained athletes was compared with that of 1120 control
athletes. There were significant improvements in the drop-jump test, (p < 0.0001, effect size
[ES] 0.97), the single-leg triple crossover hop (p < 0.0001, ES 0.47), the t-test
(p < 0.0001, ES 0.64), the multi-stage fitness test (p < 0.0001, ES 0.57), hamstring strength
(p < 0.0001), and quadriceps strength (p < 0.01). The trained athletes had a significant
reduction in the noncontact ACL injury incidence rate compared with the controls (1 ACL
injury in 36,724 athlete-exposures [0.03] and 13 ACL injuries in 61,244 exposures [0.21],
respectively, p = 0.03). The neuromuscular retraining program was effective in reducing
noncontact ACL injury rate and improving athletic performance indicators.