Achilles Tendon Elasticity and Deformation Patterns in Young and Middle-Aged Adults Evaluated Using Quantitative Ultrasound Approaches

Links

Abstract

Tendon injuries can be debilitating, and injury incidence is linked with aging. The Achilles tendon complex is particularly susceptible to injury during middle-age (e.g. tendinopathy), though the effects of aging on tendon mechanics are poorly understood. In fact, recent in vivo studies aiming to measure the effects of aging on Achilles tendon stiffness have shown contradictory results. These inconsistencies may arise due to limitations in methodological approaches, which often focus on the evaluation of gross tissue motion and may mask complex deformation patterns. Thus, the purpose of this dissertation was to utilize innovative ultrasound approaches to quantify high resolution in vivo tendon deformations and muscle-tendon mechanical properties in young and middle-aged adults. Using ultrasound elastography, we observed complex deformation patterns within the Achilles tendon, with deep portions of the tendon observed to undergo significantly more displacement than superficial portions. These non-uniform deformation patterns persisted with altered loading conditions and knee flexion angles, and may reflect variable motion between the tendon fascicles arising from the soleus and gastrocnemius muscles. We also observed small, but significant, posture- and load-dependent changes in displacement magnitudes. Supersonic Shear Imaging was used separately to characterize stretch-dependent variations in shear wave speed along the Achilles tendon and aponeurosis. Tendon shear wave speed increased with passive stretch, likely reflecting its strain-stiffening behavior, and varied significantly along the tendon length, with the proximal tendon (i.e. gastrocnemius aponeurosis) exhibiting lower shear wave speeds than the distal tendon (i.e. free tendon). Performing the same tasks, middle-aged adults exhibited evidence of significantly more uniform tendon deformation patterns and an increase in tendon compliance. The results of this dissertation demonstrate that Achilles tendon mechanics are highly non-uniform and change with age, highlighting the importance of using high resolution quantitative ultrasound techniques to assess spatial variations in tendon properties. Age-related changes in tendon mechanics were also observed to occur near regions prone to injury (e.g. the gastrocnemius aponeurosis). These observations suggest a link between the effects of aging on tendon mechanics and injury development, though future work will be critical to interpret these results in the context of injury and rehabilitation.

Cited Works (11)

Year	Entry
2007	Kubo K, Morimoto M, Komuro T, Tsunoda N, Kanehisa H, Fukunaga T. Age-related differences in the properties of the plantar flexor muscles and tendons. Med Sci Sports Exer. March 2007;39(3):541-547.
2005	Sharma P, Maffulli N. Tendon injury and tendinopathy: healing and repair. J Bone Joint Surg. January 2005;87A(1):187-202.
2011	Duenwald S, Kobayashi H, Frisch K, Lakes R, Vanderby R Jr. Ultrasound echo is related to stress and strain in tendon. J Biomech. February 3, 2011;44(3):424-429.
2005	Kobayashi H, Vanderby R. New strain energy function for acoustoelastic analysis of dilatational waves in nearly incompressible, hyper-elastic materials. J Appl Mech. November 2005;72(6):843-851.
2011	Kongsgaard M, Nielsen CH, Hegnsvad S, Aagaard P, Magnusson SP. Mechanical properties of the human Achilles tendon, in vivo. Clin Biomech (Bristol, Avon). August 2011;26(7):772-777.
2003	Lynch HA, Johannessen W, Wu JP, Jawa A, Elliott DM. Effect of fiber orientation and strain rate on the nonlinear uniaxial tensile material properties of tendon. J Biomech Eng. October 2003;125(5):726-731.
2011	Vergari C, Pourcelot P, Holden L, Ravary-Plumioën B, Gerard G, Laugier P, Mitton D, Crevier-Denoix N. True stress and Poisson's ratio of tendons during loading. J Biomech. February 24, 2011;44(4):719-724.
2004	Fleming BC, Beynnon BD. In vivo measurement of ligament/tendon strains and forces: a review. Ann Biomed Eng. 2004;32(3):318-328.
1994	Blevins FT, Hecker AT, Bigler GT, Boland AL, Hayes WC. The effects of donor age and strain rate on the biomechanical properties of bone-patellar tendon-bone allografts. Am J Sports Med. 1994;22(3):328-333.
1989	Zajac FE. Muscle and tendon: properties, models, scaling, and application to biomechanics and motor control. Crit Rev Biomed Eng. 1989;17(4):359-411.
2012	Duenwald-Kuehl S, Lakes R, Vanderby R Jr. Strain-induced damage reduces echo intensity changes in tendon during loading. J Biomech. June 1, 2012;45(9):1607-1611.