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Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Journal of Biomechanics, , Volume 42, Issue 3, 9 February 2009, Pages 280-285
Valgus moments on the knee joint during single-leg landing have been suggested as a risk factor for anterior cruciate ligament (ACL) injury. The purpose of this study was to test the influence of isolated valgus moment on ACL strain during single-leg landing. Physiologic levels of valgus moments from an in vivo study of single-leg landing were applied to a three-dimensional dynamic knee model, previously developed and tested for ACL strain measurement during simulated landing. The ACL strain, knee valgus angle, tibial rotation, and medial collateral ligament (MCL) strain were calculated and analyzed. The study shows that the peak ACL strain increased nonlinearly with increasing peak valgus moment. Subjects with naturally high valgus moments showed greater sensitivity for increased ACL strain with increased valgus moment, but ACL strain plateaus below reported ACL failure levels when the applied isolated valgus moment rises above the maximum values observed during normal cutting activities. In addition, the tibia was observed to rotate externally as the peak valgus moment increased due to bony and soft-tissue constraints. In conclusion, knee valgus moment increases peak ACL strain during single-leg landing. However, valgus moment alone may not be sufficient to induce an isolated ACL tear without concomitant damage to the MCL, because coupled tibial external rotation and increasing strain in the MCL prevent proportional increases in ACL strain at higher levels of valgus moment. Training that reduces the external valgus moment, however, can reduce the ACL strain and thus may help athletes reduce their overall ACL injury risk.
Injuries to the anterior cruciate ligament (ACL) frequently occur during the deceleration phase of landing or in preparation for a change of direction (Boden et al., 2000; Griffin et al., 2000). Females who participate in sports that include jumping and cutting often suffer from ACL injuries significantly higher than males (Agel et al., 2005; Gwinn et al., 2000). Recent studies have suggested that the gender difference in dynamic frontal-plane motion during landing may be associated with higher ACL injury rates in females: women often land with more valgus frontal-plane alignment than men and this valgus alignment caused larger valgus moments to the knee joint (Chaudhari et al., 2003; Kernozek et al., 2005; McLean et al., 2005). A prospective study has shown that female athletes who subsequently ruptured the ACL performed jump landing tasks with significantly higher valgus moments than athletes who did not rupture their ACL (Hewett et al., 2005). However, it remains unknown how much these observed gender differences in dynamic valgus alignment and valgus moments increase ACL strain during landing. Several studies have shown that valgus loading at the knee joint can increase ACL force (Fukuda et al., 2003; Hollis et al., 1991; Markolf et al., 1995). In contrast, some other studies have not observed significant ACL strain under valgus loading (Bendjaballah et al., 1997; Fleming et al., 2001). Another study observed no significant ACL strain until the medial collateral ligament (MCL) was torn by valgus loading (Mazzocca et al., 2003). However, these previous studies were often performed while constraining other degrees of freedom (DOFs) or by applying valgus loading without shear forces that occur during landing. Further, cadaver studies which predict static characteristics of the knee joint under low levels of loading may not predict ACL rupture under the large loading magnitudes and loading rates experienced during sports activities. In vivo studies of ACL strain during injury-causing events are not feasible for human subjects, either. Dynamic three-dimensional simulation studies offer an attractive alternative, because they can include more joint complexity, allow unconstrained motion, and permit physiologic loads to be applied. However, predictions of ACL strain during dynamic landing have not been previously studied using a model validated for the estimation of ACL strain. The purpose of this study was to test the influence of isolated valgus moment on ACL strain during single-leg landing using a dynamic three-dimensional simulation model driven by in vivo human loading data.