title: Non-uniform displacements within the Achilles tendon observed during passive and eccentric loading.
abstract: The goal of this study was to investigate Achilles tendon tissue displacement patterns under passive and eccentric loading conditions. Nine healthy young adults were positioned prone on an examination table with their foot secured to a rotating footplate aligned with the ankle. Subjects cyclically rotated their ankle over a 25° range of motion at 0.5 Hz. An inertial load geared to the footplate induced eccentric plantarflexor contractions with dorsiflexion. Passive cyclic ankle motion was also performed over the same angular range of motion. An ultrasound transducer positioned over the distal Achilles tendon was used to collect radiofrequency (RF) images at 70 frames/s. Two-dimensional ultrasound elastographic analysis of the RF data was used to track tendon tissue displacements throughout the cyclic motion. Non-uniform tissue displacement patterns were observed in all trials, with the deeper portions of the Achilles tendon consistently exhibiting larger displacements than the superficial tendon (average of 0.9-2.6mm larger). Relative to the passive condition, eccentric loading consistently induced smaller tissue displacements in all tendon regions, except for the superficial tendon in a flexed knee posture. Significantly greater overall tissue displacement was observed in a more extended knee posture (30°) relative to a flexed knee posture (90°). These spatial- and posture-dependent displacement patterns suggest that the tendon undergoes non-uniform deformation under in vivo loading conditions. Such behavior could reflect relative sliding between the distinct tendon fascicles that arise from the gastrocnemius and soleus muscles.
authors.affiliation: Department of Biomedical Engineering, University of Wisconsin-Madison, WI, USA. Electronic address: laura.c.slane@gmail.com.
authors.forename: Laura Chernak
authors.initials: LC
authors.lastname: Slane
authors.affiliation: Department of Biomedical Engineering, University of Wisconsin-Madison, WI, USA; Department of Mechanical Engineering, University of Wisconsin-Madison, WI, USA; Department of Orthopedics and Rehabilitation, University of Wisconsin-Madison, WI, USA.
authors.forename: Darryl G
authors.initials: DG
authors.lastname: Thelen
mesh_terms: D000125:Achilles Tendon / Q000000981:diagnostic imaging / Q000502:physiology*; D000328:Adult; D000843:Ankle Joint / Q000000981:diagnostic imaging / Q000502:physiology*; D054459:Elasticity Imaging Techniques; D005260:Female; D005528:Foot / Q000502:physiology; D006801:Humans; D007719:Knee Joint / Q000502:physiology; D008297:Male; D009038:Motion; D018482:Muscle, Skeletal / Q000502:physiology; D011187:Posture / Q000502:physiology; D016059:Range of Motion, Articular / Q000502:physiology; D055815:Young Adult
keywords: Achilles tendon; Non-uniform motion; Ultrasound elastography