Background Excessive dynamic knee valgus may leave athletes prone to serious knee injuries. The Star Excursion Balance Test (StarReach) is an objective clinical test, well applicable for non-clinicians, to identify athletes with ankle instability, but it's potential to detect athletes with reduced knee control has not been examined.

Objective To compare StarReach test performance with subjective assessment of dynamic knee valgus during a single-leg squat in female athletes.

Design Controlled, laboratory study.

Setting Norwegian female elite team handball and football.

Participants This study is part of an ongoing cohort study aimed at investigating risk factors for non-contact anterior cruciate ligament injuries. Since 2007, a total of 321 handball and 246 football players (22±4 years) have been included.

Main outcome measures A physiotherapist assessed how well players stabilised their knees while performing a single-leg squat, and scored their performance as ‘good’, ‘reduced’ or ‘poor’. Maximum reach distances in the StarReach test were measured on both feet in the antero-, medio- and posterolateral directions. A total of 440 players were tested.

Results StarReach test performance (reach distance adjusted for leg length) was significantly better for those players who were scored with ‘good’ versus ‘poor’ knee stability (p<0.01): anterolateral direction 100.1 cm (SD 8.7 cm) vs 92.0 (9.4) right and 93.4 (6.4) vs 88.7 (7.3) left knee; mediolateral 96.7 (6.7) vs 91.0 (7.8) right and 97.1 (6.2) vs 90.3 (6.9) left knee; posterolateral 105.7 (6.5) vs 98.9 (8.7) right and 106.0 (6.2) vs 98.7 (7.8) left knee. However, correlation coefficients between objective and subjective tests varied between 0.18 and 0.32 for knee stability.

Conclusion Poor relationships between StarReach-test performance and subjective scores illustrate why these two tests cannot be used interchangeably to assess knee stability. Further investigations are needed to determine whether any of these tests can predict increased knee injury risk.