Computed gastrocnemius muscle moment arm based on wrapping objects derived from 3D ultrasound: Exploring the impact of ankle position and predictability of anthropometrics

Abstract

The objective of this study was to evaluate the effectiveness of subject-specific wrapping objects (SS.WOs) derived from 3D ultrasound measurements in calculating the musculotendon moment arm, particularly the lateral gastrocnemius muscle moment arm at the knee (Gas.lat KMA). Computed musculoskeletal modeling, essential for understanding human locomotion, often shows discrepancies compared to in vivo measurements. This research investigated whether SS.WOs, tailored to individual muscle paths across different joint configurations, could mitigate these discrepancies. Ten healthy participants were subjected to 3D ultrasound to record the Gas.lat path at various knee and ankle angles. This data was utilized to develop SS.WOs in a scaled Rajagopal Full-body model (SS-Rajagopal). We assessed the impact of the modeling approach and ankle position on the computed Gas.lat KMA by comparing it with results from two scaled generic models (SC-Rajagopal and SC-Gait2392). There was no significant effect of ankle position on Gas.lat KMA across all knee angles; however, the choice of modeling approach markedly influenced the outcomes. The computed Gas.lat KMA from SS-Rajagopal more closely matched in vivo measurements at higher knee angles compared to SC-Rajagopal. Significant correlations were observed between the computed Gas.lat KMA from both SS-Rajagopal and SC-Rajagopal with anthropometric measurements. However, no correlation was found between the properties of SS.WOs and individual anthropometrics. In conclusion, while optimization techniques such as muscle path computation with WOs improve musculoskeletal modeling efficiency, they may not fully address inter-subject variability.