Background

Although knee valgus is one of the causes of injury during cutting motion in non-contact anterior cruciate ligament (ACL) injuries, preventative measures have not been established. A previous study reported the use of foot orthosis as a potentially effective solution. Walter L et al. reported that athletes without foot orthosis were 7.14 times more likely to sustain an ACL injury than that with foot orthosis group. This study speculates that the medial arch may have decreased hindfoot valgus angle and corrected the knee's valgus, resulting in less ACL injury. however, there has been no analytical research on actual movements during sports activities using foot orthosis. Therefore, the purpose of this study was to examine the effect of medially posted foot orthoses on lower extremity kinematics in female athletes.

Methods

A total of 16 female collegiate-level athletes who played basketball or volleyball volunteered to participate in this study. The mean age was 20.3 years. Participants were asked to perform a 30° sidestep cut off from the right leg motion performance institute laboratory with 3 different medial arch height orthoses, comprising of 1) a full flat insole without medial arch support, 2) commercially available foot orthosis with general height arch support, and 3) foot orthosis with double the common height for arch support to observe the effect on the knee when overcorrected. To minimize the effect of the shoe sole on the lower limb kinematics, a shoe with a thin sole was selected. Participants were asked to complete 3 acceptable trials of the running task on each foot orthosis. A markerless motion capture system combined with 2 force plate was used to collect full body kinematics and lower limb kinetics. Kinematics and kinetics of the knee joint was compared between the three types of foot orthoses by analysis of variance (ANOVA).

Results

With the double-height medial arch support foot orthosis, the knee valgus angle at initial contact was significantly lower than with other insoles. There was no difference of valgus angle at peak contact and maximum valgus angle between the three groups. The other kinematics and kinetics measurements did not differ between the three groups.

Conclusion

Although the general height of the foot orthosis did not affect the kinematics of the knee joint, overcorrection with higher foot orthosis improved the valgus angle of the knee joint.