A knee wobbling phenomenon during four squatting and landing tasks as potential screening tasks for detecting a risk factor of ACL injury

[Objective] The purpose of this study was to detect the differences in the presence and movement of a knee wobbling phenomenon (KWP) during four squatting and landing tasks in order to establish the optimal screening task for identifying a potential indicator of ACL injury risk. [Background] KWP consists of quick and uncontrollable medio-lateral movements(valgus/varus) of the knee,which may indicate an elevated risk for ACL injury. [Materials &Methods] Ten female collegiate athletes participated in this study. Slow single leg squat(SSLS) ,single leg standing(SLS), double leg drop landing from a 30-cm box(DLB),and repeated single leg landing after jumping(RSLJ) were analyzed. Relative valgus(frontal) angular velocity divided by flexion(sagittal) angular velocity(F/S ratio) was calculated. An F/S ratio exceeding 100% was defined as “F/S spike” indicating KWP. [Results] The number of valgus and varus F/S spikes were significantly different between the four tasks (p＜.001). The median(range) of the initial knee flexion angles during SSLS,SLS,DLB,and RSLJ was 0.1(0-4.3)°,9.1(3.8-14.5)°,25.5(13.6-46.9)°,and 19.6(14.4-34.5)°,respectively(p＜.001). The median for the number of F/S spikes during each task was 4.5(0.3-7.3), 5.9(4.6-7.0), 0, and 0(0-0.5) times,respectively (p＜.001). [Conclusion] SSLS and SLS induced knee wobbling at low knee flexion angles(i.e.＜25°), which facilitated recognition of the characteristics of knee movement at low flexion angles.