title: A 3D model of the Achilles tendon to determine the mechanisms underlying nonuniform tendon displacements.
abstract: The Achilles is the thickest tendon in the body and is the primary elastic energy-storing component during running. The form and function of the human Achilles is complex: twisted structure, intratendinous interactions, and differential motor control from the triceps surae muscles make Achilles behavior difficult to intuit. Recent in vivo imaging of the Achilles has revealed nonuniform displacement patterns that are not fully understood and may result from complex architecture and musculotendon interactions. In order to understand which features of the Achilles tendon give rise to the nonuniform deformations observed in vivo, we used computational modeling to predict the mechanical contributions from different features of the tendon. The aims of this study are to: (i) build a novel computational model of the Achilles tendon based on ultrashort echo time MRI, (ii) compare simulated displacements with published in vivo ultrasound measures of displacement, and (iii) use the model to elucidate the effects of tendon twisting, intratendon sliding, retrocalcaneal insertion, and differential muscle forces on tendon deformation. Intratendon sliding and differential muscle forces were found to be the largest factors contributing to displacement nonuniformity between tendon regions. Elimination of intratendon sliding or muscle forces reduced displacement nonuniformity by 96% and 85%, respectively, while elimination of tendon twist and the retrocalcaneal insertion reduced displacement nonuniformity by only 35% and 3%. These results suggest that changes in the complex internal structure of the tendon alter the interaction between muscle forces and tendon behavior and therefore may have important implications on muscle function during movement.
authors.affiliation: Department of Biomedical Engineering, University of Virginia, United States; Auckland Bioengineering Institute, University of Auckland, New Zealand.
authors.forename: Geoffrey G
authors.initials: GG
authors.lastname: Handsfield
authors.affiliation: Department of Biomedical Engineering, University of Virginia, United States.
authors.forename: Joshua M
authors.initials: JM
authors.lastname: Inouye
authors.affiliation: Department of Biomedical Engineering, University of Wisconsin-Madison, United States; Institute for Orthopaedic Research and Training, Katholieke Universiteit Leuven, Belgium.
authors.forename: Laura C
authors.initials: LC
authors.lastname: Slane
authors.affiliation: Department of Biomedical Engineering, University of Wisconsin-Madison, United States; Department of Mechanical Engineering, University of Wisconsin-Madison, United States.
authors.forename: Darryl G
authors.initials: DG
authors.lastname: Thelen
authors.affiliation: Department of Radiology and Medical Imaging, University of Virginia, United States.
authors.forename: G Wilson
authors.initials: GW
authors.lastname: Miller
authors.affiliation: Department of Biomedical Engineering, University of Virginia, United States; Department of Orthopaedic Surgery, University of Virginia, United States; Department of Mechanical and Aerospace Engineering, University of Virginia, United States. Electronic address: ssblemker@virginia.edu.
authors.forename: Silvia S
authors.initials: SS
authors.lastname: Blemker
mesh_terms: D000125:Achilles Tendon / Q000000981:diagnostic imaging / Q000502:physiology*; D000328:Adult; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008954:Models, Biological; D009068:Movement; D018482:Muscle, Skeletal / Q000502:physiology; D014463:Ultrasonography
keywords: Computational model; Connective tissue; Finite element; MRI; Soft tissue