A simple clinical screening test can identify elite female football players with increased knee valgus angles

Background A link has been suggested between increased dynamic knee valgus and the risk of anterior cruciate ligament (ACL) injuries in female athletes. However, these findings are based on complex time-consuming 3D motion analysis. There is a need for simple screening tools to identify athletes at increased risk of an ACL rupture. Objective To assess whether an experienced clinician can identify athletes with increased valgus angles and moments during a vertical drop jump using a simple screening test. Design Cross-sectional study. Participants Elite female football players. Methods Players in the Norwegian elite league (12 teams) were screened for potential risk factors for ACL injuries. Knee kinematics and kinetics in the landing phase of a 30 cm vertical drop jump were calculated using 3D motion analysis. Using a similar jump task, a physiotherapist assessed how well players stabilised their knees, and scored their knee control as ‘good’, ‘reduced’ or ‘poor’. Results Of the 136 players included, 38% were classified as ‘good’, 34% had ‘reduced’ control and 28% were scored as ‘poor’. Players with good control had significantly lower maximal valgus angles compared to players with poor control (0.5° vs 6.8°, p≤0.001). There were no differences in valgus moments (0.28 Nm/kg vs 0.28 Nm/kg, p=1.0). One-fifth of all players (17.6%) displayed valgus angles more than one SD above the mean in the 3D analyses (3.1° ±4.5°). The screening test captured 87.5% of these players. 22 (16.2%) players were classified in the ‘poor’ group without displaying high valgus angles. Conclusion The screening test identified 87.5% of players with increased valgus angles. No correlation was found between valgus angles and moments, and the test could not identify players with high valgus moments. Further investigations are needed to determine the cut-off value for defining high- versus low-risk groups, as well as the predictive value of the test.