ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

NONUNIFORM MOTION IN THE ACHILLES TENDON OBSERVED USING
QUANTITATIVE ULTRASOUND ELASTOGRAPHY
1. ABSTRACT
L. Chernak 1 , D. Thelen 2
Achilles tendinopathies, which are often difficult to treat clinically, have recently been
shown to respond favorably to eccentric rehabilitative exercises. A possible underlying
mechanism to this response is that these exercises induce shear stress within the tissues
that stimulate healing responses. The purpose of this study was to use ultrasound
elastography to evaluate variations in regional tendon motion during eccentric
plantarflexor loading. Ultrasound radiofrequency (RF) data were collected from five
healthy young adults. An inertial load was used to induce eccentric plantarflexor
contractions while the subjects cyclically dorsi- and plantarflexed their ankle. The
relative recruitment of the gastrocnemius and soleus muscles was modulated by
collecting data while the subject was in both an extended and flexed knee posture.
Tendon tissue motion was computed using two-dimensional (2D) cross-correlations to
track frame-to-frame displacements of the ultrasound speckle pattern visible within the
tendon. During eccentric loading, we found evidence of non-uniform tissue motion with
the deep (anterior) region of the tendon undergoing significantly greater motion than
superficial (posterior) region of the tendon. Tendon motion was significantly diminished
in a flexed knee posture, which could reflect greater soleus loading and stretch of the
distal free tendon. The non-uniform tissue motion observed supports the hypothesis that
shear deformations are induced during lengthening plantarflexor muscle contractions.
2. INTRODUCTION
Tendinopathy is a common overuse injury that is both painful and challenging to
resolve clinically (Maffulli, et al. 2008, Longo, et al. 2008, Maffulli, et al. 2004). Recent
studies show that eccentric exercises may enhance the healing of tendinopathies
(Alfredson 2003), though the underlying mechanisms are not understood. Anatomically,
the Achilles tendon extends from the distal gastrocnemius muscle-tendon junction to its
insertion at the calcaneus (Fig. 1). The Achilles tendon is shared between the
gastrocnemius, which tends to insert on the superficial side of the tendon, and the
soleus, which tends to insert more deeply and closer to the calcaneus (O'Brien 1984).
Achilles injuries commonly occur in characteristic locations (deep edge 3-5 cm
proximal to the calcaneus (Jozsa, et al. 1989, Gibbon, et al. 2000)), which may be due in
part to the nonuniform tendon loading (Arndt, et al. 1998) and shear deformations
which occur as a result of this complex anatomy.
Numerous prior studies have used cine ultrasound imaging to track tendon tissue motion
1
PhD Student, Department of Biomedical Engineering, University of Wisconsin-Madison, 1513
University Ave, Madison, WI 53706
2
Professor, Department of Mechanical Engineering, University of Wisconsin-Madison, 1513 University
Ave, Madison, WI 53706