Is Knee Separation During a Drop Jump Associated With Lower Extremity Injury in Adolescent Female Soccer Players?

Area of Science:

• Sports Medicine
• Biomechanics
• Injury Epidemiology

Background:

• Knee injuries are prevalent in adolescent and adult female soccer players.
• Abnormal valgus knee appearance, indicated by low normalized knee separation (NKS), is a suspected risk factor.
• Normal NKS ranges in younger athletes and its injury risk association remain unclear.

Purpose of the Study:

• Determine normal NKS ranges in perimenarchal female youth soccer players using a drop-jump test.
• Investigate if low NKS correlates with increased risk of lower extremity or knee injuries.

Main Methods:

• A prospective cohort study followed 351 female youth soccer players (ages 11-14) for one season.
• Preseason drop-jump testing assessed NKS; injuries were tracked via an online surveillance system.
• Poisson regression analyzed the association between NKS (categorized by percentile and SD) and injury risk, stratified by menarche.

Main Results:

• 134 players sustained 173 lower extremity injuries, including 43 knee injuries.
• Postmenarchal players with NKS ≤10th percentile showed significantly higher risks for lower extremity (RR 1.92) and knee injuries (RR 3.62).
• Lower NKS (1 SD decrease) at landing and takeoff was associated with increased knee injury risk (RR 1.80 and 1.66, respectively) in postmenarchal players.

Conclusions:

• Low normalized knee separation (NKS) is a significant risk factor for lower extremity and knee injuries in postmenarchal female youth soccer players.
• No significant association between NKS and injury risk was found in premenarchal players.
• Findings suggest NKS assessment may aid in identifying at-risk postmenarchal athletes.