Comparison of markerless and marker-based motion analysis accounting for differences in local reference frame...

Area of Science:

• Biomechanics
• Motion Analysis
• Kinesiology

Background:

• Markerless motion capture offers an alternative to marker-based systems.
• Previous studies reported kinematic signal differences between markerless and marker-based systems.
• The cause of these discrepancies, specifically reference frame alignment, remains under-assessed.

Purpose of the Study:

• To systematically assess if reference frame alignment inconsistencies explain differences between markerless and marker-based kinematic signals.
• To apply a reference frame alignment method (REFRAME) to markerless knee kinematic data.
• To determine the impact of REFRAME on the agreement between markerless and marker-based kinematic data.

Main Methods:

• Ten healthy subjects performed walking trials.
• Simultaneous data acquisition using markerless (Theia3D) and marker-based (Qualisys) systems.
• Application of the REFRAME method to align local coordinate systems and kinematic analysis in Visual3D.

Main Results:

• REFRAME optimized markerless kinematic signals, involving average rotations of the tibia and femur coordinate systems.
• Post-REFRAME analysis showed improved agreement between markerless and marker-based data across all planes.
• Root-mean-square error significantly decreased in sagittal, frontal, and transverse planes.

Conclusions:

• Most differences between markerless and marker-based kinematic data are likely due to local frame orientation inconsistencies.
• The REFRAME method effectively reduces discrepancies, enhancing the reliability of markerless motion analysis.
• Markerless kinematic signals fundamentally represent similar underlying motion waveforms as marker-based systems.