Reliability and concurrent validity between two-dimensional and three-dimensional evaluations of knee valgus during...

Area of Science:

• Biomechanics
• Sports Medicine
• Kinesiology

Background:

• Frontal plane knee kinematics are crucial for assessing injury risk.
• Two-dimensional (2D) video analysis offers a potentially cost-effective alternative to three-dimensional (3D) motion capture.
• Establishing the validity and reliability of 2D methods is essential for clinical application.

Purpose of the Study:

• To determine the concurrent validity and reliability of four 2D video-based techniques for quantifying frontal plane knee kinematics.
• To compare 2D measures against a 3D system during a double-legged drop jump.
• To assess the effectiveness of 2D analysis for measuring knee valgus.

Main Methods:

• Sixteen healthy participants performed a 40 cm double-legged drop jump.
• Four 2D measures (two frontal plane projection angles, knee-to-ankle separation ratio [KASR], knee separation distance [KSD]) were assessed.
• 2D measures were compared against a 3D system, with novice physical therapists performing the analyses.

Main Results:

• All four 2D measures demonstrated good to excellent reliability (ICC: 0.89-0.99).
• KASR and KSD showed excellent correlation with 3D measures (ICC: 0.96 and 0.94, respectively).
• Frontal plane projection angles exhibited poor to moderate correlation with 3D measures (ICC: 0-0.57).

Conclusions:

• 2D KASR and KSD are reliable and valid methods for evaluating knee valgus.
• These 2D measures demonstrate high correlation with 3D techniques.
• 2D KASR and KSD provide a cost-effective approach for assessing frontal plane knee kinematics.