Utility of 2D Video Analysis for Assessing Frontal Plane Trunk and Pelvis Motion during Stepping, Landing, and Change in Direction Tasks: A Validity Study.
Rachel K Straub, Christopher M Powers
PMID 35136682WHAT IT FOUND
2D video analysis correlates strongly with 3D motion capture for trunk and pelvis angles during dynamic tasks.
While useful for clinical screening, wide limits of agreement mean 2D measures lack the precision required for high-accuracy assessment, especially during change-of-direction movements.
Key findings
012D video measures of frontal plane trunk angles showed strong to very strong correlations with 3D motion analysis across all tasks.
022D video measures of frontal plane pelvis angles showed moderate to strong correlations with 3D motion analysis.
03Bland-Altman analysis revealed wide 95% limits of agreement for both trunk and pelvis, indicating limited precision for individual patient assessment despite good correlation.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
The study only included healthy athletes, so the validity of 2D measures in patients with pain or injury is unknown. The 2D measures were taken from a single frame (peak knee flexion or heel contact), which may not capture the full dynamic range of motion. Reliability of the 3D measures (the reference standard) was not reported, which could affect the agreement analysis. The wide limits of agreement mean that a single 2D measurement could differ from the true 3D value by more than 10 degrees in some cases. The study did not assess whether 2D measures predict injury risk, only their correlation with 3D kinematics.
Declared interests
The authors declared no conflicts of interest. The study was approved by the Institutional Review Board of the Health Sciences Campus at the University of Southern California. No specific funding source was declared in the provided text.
The easy way to misread this
Do not assume that because 2D and 3D measures are correlated, they are interchangeable for individual patients. The wide limits of agreement mean that a specific 2D angle reading may be inaccurate by over 10 degrees compared to 3D, so use 2D for screening patterns, not for precise quantitative assessment.