Experimental recommendations for estimating lower extremity loading based on joint and activity

Abstract

Researchers often estimate joint loading using musculoskeletal models to solve the inverse dynamics problem. This approach is powerful because it can be done non-invasively, however, it relies on assumptions and physical measurements that are prone to measurement error. The purpose of this study was to determine the impact of these errors - specifically, segment mass and shear ground reaction force - have on analyzing joint loads during activities of daily living. We performed traditional marker-based motion capture analysis on 8 healthy adults while they completed a battery of exercises on 6 degree of freedom force plates. We then scaled the mass of each segment as well as the shear component of the ground reaction force in 5% increments between 0 and 200% and iteratively performed inverse dynamics calculations, resulting in 1681 mass-shear combinations per activity. We compared the peak joint moments of the ankle, knee, and hip at each mass-shear combination to the 100% mass and 100% shear combination to determine the percent error. We found that the ankle was most resistant to changes in both mass and shear and the knee was resistant to changes in mass while the hip was sensitive to changes in both mass and shear. These results can help guide researchers who are pursuing lower-cost or more convenient data collection setups.

Keywords: Biomechanics; Inverse dynamics; Low-cost data collection; Run; Sensitivity analysis; Walk.

Figure 1 (1 column):

We defined participant-specific models (left leg hidden for clarity) by scaling a generic musculoskeletal model to fit anatomic markers placed over the pelvis, condyles, malleoli, and metatarsal heads. We included additional markers on each body segment to improve labeling and inverse kinematic fidelity.

Figure 2 (2 column):

Errors in peak joint moment for each mass-shear combination are visualized as heat maps for the hip, knee, and ankle for each of the analyzed motions. Each pixel of a given heat map represents the percent error between a mass-shear combination and the ground truth combination, with pale yellow representing 0%, and deep red and blue representing <−30% and >30% error, respectively. The x-axis of the heat maps is the mass scalar and the y-axis is the shear scalar.

Figure 3 (1.5 column):

Experimental recommendations to achieve desired joint loading fidelity. Scenarios where there was less than 10% error compared to ‘ground truth’ calculations from inverse dynamics (100% mass and 100% GRFshear) are demarked with a check mark. 0% mass conditions represent experimental techniques that quantify body ‘pose’ and do not quantify segmental dynamics. 0% GRFshear represent experimental conditions that may utilize low-cost force plates that only measure the vertical reaction force.