Dynamic Lower Limb Alignment During Jumping in Preschool Children: Normative Profiles and Sex Differences

The natural development of static lower limb varus/valgus alignments during early childhood is well understood. However, our understanding of dynamic lower limb frontal plane alignments is limited, and we lack normative descriptions of this phenomenon for both boys and girls. This study investigated dynamic lower limb alignment during jump-landings in preschool children, focusing on associations with sex, age, and motor performance. Dynamic lower limb alignment was measured as the Knee-to-Ankle Separation Ratio (KASR) in 605 children aged 3-6 years using markerless motion capture. Based on KASR measurements, we categorized the children into three kinematic groups: Valgus, Intermediate, and Varus. Median KASR scores were 0.86 (0.80-0.96) overall, 0.89 (0.81-0.98) for boys, and 0.85 (0.78-0.92) for girls. Over 75% of the children exhibited some level of dynamic knee valgus during jump-landings (KASR < 1). However, roughly two-thirds of the children in the Valgus group were girls. Age-adjusted differences in motor performance were small and only statistically significant for jump height and length in girls. These findings suggest that dynamic knee valgus during jump-landings is a common occurrence in preschool children, especially among girls. The potential relationship between dynamic lower limb alignment and age and motor performance warrants further investigation.