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British Journal of Sports Medicine


Background: Increased knee valgus predicts the risk of anterior cruciate ligament (ACL) injury, particularly in women. Reducing injury rates thus relies on detecting and continually evaluating people with relatively large valgus motions.

Objectives: To examine the potential of a two dimensional (2D) video analysis method for screening for excessive valgus.

Methods: Ten female and 10 male National Collegiate Athletic Association basketball players had three dimensional (3D) knee valgus and two dimensional (2D) frontal plane knee angle quantified during side step, side jump, and shuttle run tasks. 3D valgus was quantified from external marker coordinates using standard techniques, and 2D data were obtained from both the frontal plane projections of these coordinates (2D-Mot) and manual digitisation of digital video footage (2D-Cam). A root mean square (RMS) error was calculated between 2D-Mot and 2D-Cam data to evaluate the reliability of the latter. Correlations between 2D-Cam and 3D data (intersubject and intrasubject) were also conducted, and regression slope and r2 values obtained.

Results: 2D-Cam and 2D-Mot data were consistent for side step (RMS  =  1.7°) and side jump (RMS  =  1.5°) movements. Between subjects, 2D-Cam and 3D data correlated well for the side step (r2  =  0.58) and side jump (r2  =  0.64). Within subjects, 2D-Cam and 3D data correlated moderately for the side step (r2  =  0.25 (0.19)) and side jump (r2  =  0.36 (0.27)).

Conclusions: The 2D-Cam method can be used to screen for excessive valgus in elite basketball players, particularly for movements occurring primarily in the frontal plane. This method may also be a useful training evaluation tool when large reductions in dynamic valgus motions are required.


This work was supported by US National Institutes of Health (grants R01 AR47039 (to AJV) and R01 AR049735-01 (to TEH)).