The influence of muscle pennation angle and cross-sectional area on contact forces in the ankle joint

Ran S Sopher,Andrew A Amis,D Ceri Davies,Jonathan Rt Jeffers

doi:10.1177/0309324716669250

Ran S Sopher, Andrew A Amis + Show 2 more

Open Access

https://doi.org/10.1177/0309324716669250

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Abstract

Data about a muscle’s fibre pennation angle and physiological cross-sectional area are used in musculoskeletal modelling to estimate muscle forces, which are used to calculate joint contact forces. For the leg, muscle architecture data are derived from studies that measured pennation angle at the muscle surface, but not deep within it. Musculoskeletal models developed to estimate joint contact loads have usually been based on the mean values of pennation angle and physiological cross-sectional area.Therefore, the first aim of this study was to investigate differences between superficial and deep pennation angles within each muscle acting over the ankle and predict how differences may influence muscle forces calculated in musculoskeletal modelling. The second aim was to investigate how inter-subject variability in physiological cross-sectional area and pennation angle affects calculated ankle contact forces.Eight cadaveric legs were dissected to excise the muscles acting over the ankle. The mean surface and deep pennation angles, fibre length and physiological cross-sectional area were measured. Cluster analysis was applied to group the muscles according to their architectural characteristics. A previously validated OpenSim model was used to estimate ankle muscle forces and contact loads using architecture data from all eight limbs.The mean surface pennation angle for soleus was significantly greater (54%) than the mean deep pennation angle. Cluster analysis revealed three groups of muscles with similar architecture and function: deep plantarflexors and peroneals, superficial plantarflexors and dorsiflexors. Peak ankle contact force was predicted to occur before toe-off, with magnitude greater than five times bodyweight. Inter-specimen variability in contact force was smallest at peak force.These findings will help improve the development of experimental and computational musculoskeletal models by providing data to estimate force based on both surface and deep pennation angles. Inter-subject variability in muscle architecture affected ankle muscle and contact loads only slightly. The link between muscle architecture and function contributes to the understanding of the relationship between muscle structure and function.

Highlights

A muscle’s architecture ( its physiological cross-sectional area (PCSA), fibre pennation angle (PA) and optimal fibre length) is an established predictor of its force generation and excursion,[1] in both musculotendon-actuator-2,3 and electromyography (EMG)-activation-data based[4] models
This would result in a 15% underestimation of the force exerted by soleus when calculated using surface rather than deep PA measurements and assuming that the muscle force is proportional to the cosine of the PA.[4]
The muscle-architecture data reported here may be used to estimate muscle forces through musculoskeletal modelling, which can contribute to the understanding of the roles of the leg muscles and assist in surgical decision-making and ankle prosthesis design

Summary

Introduction

A muscle’s architecture ( its physiological cross-sectional area (PCSA), fibre pennation angle (PA) and optimal fibre length) is an established predictor of its force generation and excursion,[1] in both musculotendon-actuator-2,3 and electromyography (EMG)-activation-data based[4] models. Similar to previous studies,[24,28] only surface measurements of muscle PAs were performed, despite the fact that there is evidence suggesting that there may be a difference between the PAs at the surface and the interior of a muscle,[29] for bi- or multi-pennate muscles with large PCSAs. Musculoskeletal models[12,25] use a number of elements to simulate the forces exerted by muscles, larger muscles, implying that it can be advantageous to use different architectural parameters, including PA, for each of these elements. Musculoskeletal models[12,25] use a number of elements to simulate the forces exerted by muscles, larger muscles, implying that it can be advantageous to use different architectural parameters, including PA, for each of these elements This emphasises the potential benefit of obtaining PA data for both a muscle’s surface and its interior

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