Validity of markerless motion capture for ankle kinematics in children with cerebral palsy wearing ankle-foot orthoses.
Abstract
Background
Markerless motion capture is a promising approach for gait analysis, particularly for the potential to reduce testing burden in pediatric clinical populations; however, marker-based motion capture is an imperfect benchmark, limiting interpretation of between-system comparisons. Given the use of ankle-foot orthoses (AFOs) in children with cerebral palsy (CP), the inherent constraints of AFOs provide a reference for assessing kinematic plausibility. This study evaluated the concurrent validity of Theia3D markerless motion capture for ankle kinematics in children wearing AFOs, using the known mechanical constraints to contextualize agreement between systems.
Methods
Children with CP wearing AFOs underwent concurrent marker-based and markerless gait analysis. Ankle kinematics were compared using statistical parametric mapping, root mean square deviation (RMSD), and paired t-tests of range of motion (ROM).
Results
Participants were stratified by AFO type into sagittal motion-permitting (hinged/posterior leaf-spring; n = 36 limbs) and sagittal motion-restricting (solid/ground-reaction; n = 19 limbs) groups. Both groups showed significant between-system differences across all planes. Markerless ROM exceeded marker-based ROM in the sagittal and transverse planes despite AFO constraints (sagittal plane ROM: 9° vs. 16° in sagittal motion-restricting AFOs; transverse plane ROM: 5-6° vs. 17-18°). Frontal plane differences were not accompanied by ROM disagreement.
Conclusion
Theia3D overestimates ankle ROM in children with CP wearing AFOs in the sagittal and transverse planes, exceeding device constraints. Markerless kinematic outputs may reflect ankle position anticipated by the markerless algorithm rather than true ankle position. Caution is warranted when using markerless ankle kinematics to guide clinical decision-making in this population, emphasizing the importance of population-specific validation before clinical implementation.