Date Published: June 20, 2017
Publisher: Public Library of Science
Author(s): Akihiro Tamura, Kiyokazu Akasaka, Takahiro Otsudo, Jyunya Shiozawa, Yuka Toda, Kaori Yamada, Jean L. McCrory.
Dynamic knee valgus during landings is associated with an increased risk of non-contact anterior cruciate ligament (ACL) injury. In addition, the impact on the body during landings must be attenuated in the lower extremity joints. The purpose of this study was to investigate landing biomechanics during landing with dynamic knee valgus by measuring the vertical ground reaction force (vGRF) and angular impulses in the lower extremity during a single-leg landing. The study included 34 female college students, who performed the single-leg drop vertical jump. Lower extremity kinetic and kinematic data were obtained from a 3D motion analysis system. Participants were divided into valgus (N = 19) and varus (N = 15) groups according to the knee angular displacement during landings. The vGRF and angular impulses of the hip, knee, and ankle were calculated by integrating the vGRF-time curve and each joint’s moment-time curve. vGRF impulses did not differ between two groups. Hip angular impulse in the valgus group was significantly smaller than that in the varus group (0.019 ± 0.033 vs. 0.067 ± 0.029 Nms/kgm, p<0.01), whereas knee angular impulse was significantly greater (0.093 ± 0.032 vs. 0.045 ± 0.040 Nms/kgm, p<0.01). There was no difference in ankle angular impulse between the groups. Our results indicate that dynamic knee valgus increases the impact the knee joint needs to attenuate during landing; conversely, the knee varus participants were able to absorb more of the landing impact with the hip joint.
The anterior cruciate ligament (ACL) is frequently injured during soccer, basketball, and many other sports. In recent studies, the mechanism of ACL injury has been widely considered to involve biomechanical factors [1–3]. An increased knee valgus angle during landings is one of the main causative factors for knee injuries, including injuries to the ACL [4–6]. Dynamic knee valgus, described as a combination of hip adduction, hip internal rotation, and knee abduction is recognized as a common lower extremity alignment seen in non-contact ACL injury situations [4,7,8]. Prospective studies have reported that increased knee valgus angle and knee abduction moment during landings were predictive of non-contact ACL injuries in female athletes [4,9,10]. These studies suggested the importance of knee injury prevention for athletes who land with dynamic knee valgus.
The vGRF and angular impulses in the lower extremity joints explain the net force and joint moments experienced by the lower extremity joints over periods of time during the deceleration phase of landings. From the results of our study, the subjects with dynamic knee valgus experienced greater knee angular impulse compared with those with dynamic knee varus. These findings indicate that landing with dynamic knee valgus may increase the impact on the knee joint during the deceleration phase of landings. Therefore, dynamic knee valgus during landings may be one of the biomechanical factors that reduce an individual’s capacity to attenuate the impact imposed on the knee joint during landings. Some researchers have reported that the knee and hip joints are the primary shock absorber during landings [12,17,18]. In addition, it has been shown in females that the hip extensor, knee extensor, and ankle plantar flexor muscles contribute 38, 41, and 22% of the total energy absorption, respectively . Some of these reports have indicated that the knee joint is the most important impact absorber of the lower extremities [12,17,20]. The results of the present study show that the hip angular impulse in dynamic knee valgus is smaller than that in dynamic knee varus. Therefore, the knee joint was the most important impact absorber in the participants who landed with dynamic knee valgus, while the impact absorption by the hip joint was small. In addition, the vGRF impulse represents the total impact applied to the body, including the hip, knee, and ankle joints, by the ground during landings. In this study, vGRF impulse differed between the two knee alignment groups in the frontal plane. These results indicate that the knee angular impulse in the valgus group was apparently distributed to the hip joints without changing the total impact imposed on the body during landings.
The impact on the body during the deceleration phase of landings needs to be attenuate in the lower extremity joints to create soft landings. Our study showed that landing with dynamic knee valgus resulted in a greater knee extensor angular impulse than landing with dynamic knee varus, whereas the hip extensor angular impulse was smaller. The hip, knee, and ankle angles were not affected by the difference in dynamic knee alignment in the frontal plane. These results suggest that landing with dynamic knee valgus may reduce the capacity to attenuate the impact imposed on the knee joint during the deceleration phase of landings, without changing the dynamic knee alignment in the sagittal plane. In addition, the impact on the knee joint was apparently counteracted by the capacity of the hip joint for impact absorption. These findings indicate that altering the landing strategy in motor learning could change the load on the hip and knee joints in terms of impact attenuation during landings.