Objective: To determine the association of 2-dimensional (2D) video-based techniques and 3-dimensional (3D) motion analysis to assess potential knee injury risk factors during jump landing.
Design: Observational study.
Setting: Research laboratory.
Participants: Thirty-six female athletes in cutting and pivoting sports.
Assessment of risk factors: : Athletes performed a drop vertical jump during which movement was recorded with a motion analysis system and a digital video camera positioned in the frontal plane.
Main outcome measures: The 2D variables were the frontal plane projection angle (FPPA), the angle formed between thigh and leg, and the knee-to-ankle separation ratio, the distance between knee joints divided by the distance between ankles. The 3D variables were knee abduction angle and external abduction moment. All variables were assessed at peak knee flexion. Linear regression assessed the relationship between the 2D and 3D variables. In addition, intraclass correlation coefficients (ICC) determined rater reliability for the 2D variables and compared the 2D measurements made from digital video with the same measurements from the motion analysis.
Results: : The knee-to-ankle separation ratio accounted for a higher variance of 3D knee abduction angle (r = 0.350) and knee abduction moment (r = 0.394) when compared with the FPPA (r = 0.145, 0.254). The digital video measures had favorable rater reliability (ICC, 0.89-0.94) and were comparable with the motion analysis system (ICC, ≥ 0.92).
Conclusions: When compared with the FPPA, the knee-to-ankle separation ratio had better association with previously cited knee injury risk factors in female athletes. The 2D measures have adequate consistency and validity to merit further clinical consideration in jump landing assessments.