Mechanical properties of the human Achilles tendon, in vivo

Kongsgaard, M.<sup>1</sup>; Nielsen, C. H.<sup>1</sup>; Hegnsvad, S.<sup>1</sup>; Aagaard, P.<sup>2</sup>; Magnusson, S. P.<sup>1,3</sup>

Affiliations

¹Institute of Sports Medicine, Dept. Othopedic Surgery M, Bispebjerg Hospital and Center for Healthy Aging, Faculty of Health Sciences, University of Copenhagen, Denmark

²Institute of Sports Exercise and Clinical Biomechanics, University of Southern Denmark Odense, Denmark

³Department of Physiotherapy, Bispebjerg Hospital, Copenhagen, Denmark

Abstract and keywords

Background: Ultrasonography has been widely applied for in vivo measurements of tendon mechanical properties. Assessments of human Achilles tendon mechanical properties have received great interest. Achilles tendon injuries predominantly occur in the tendon region between the Achilles-soleus myotendinous junction and Achilles-calcaneus osteotendinous junction i.e. in the free Achilles tendon. However, there has been no adequate ultrasound based method for quantifying the mechanical properties of the free human Achilles tendon. This study aimed to: 1) examine the mechanical properties of the free human Achilles tendon in vivo by the use of ultrasonography and 2) assess the between-day reproducibility of these measurements.

Methods: Ten male subjects had the Achilles tendon moment arm length, Achilles tendon cross sectional area and free Achilles tendon length determined. All subjects performed isometric plantarflexion ramp contractions to assess between-day reproducibility on two separate days. Simultaneous ultrasonography based measurements of Achilles-soleus myotendinous junction and Achilles-calcaneus osteotendinous junction displacement together with Achilles tendon force estimates yielded free Achilles tendon mechanical properties.

Findings: Free Achilles tendon maximal force, deformation and stiffness were 1924 (SD 229) N, 2.2 (SD 0.6) mm and 2622 (SD 534) N/mm on day 1. For between-day reproducibility there were no significant differences between days for free Achilles tendon mechanical properties. The between-day correlation coefficient and typical error percent were 0.81 and 5.3% for maximal Achilles tendon force, 0.85 and 11.8% for maximal Achilles tendon deformation and 0.84 and 8.8% for Achilles tendon stiffness respectively. Last, osteotendinous junction proximal displacement on average contributed with 71 (SD 12) % of proximal myotendinous junction displacement.

Interpretation: This study, for the first time, presents an ultrasonography based in vivo method for measurement of free AT mechanical properties. The method is applicable for evaluation of free human Achilles tendon mechanical properties in relation to training, injury and rehabilitation.

Keywords: Achilles tendon; Ultrasonography; Mechanical properties; Reproducibility

Links

DOI: 10.1016/j.clinbiomech.2011.02.011

PubMed: 21392868

WoS: 000293425700013

Cited Works (1)

Year	Entry
1990	Scott SH, Winter DA. Internal forces at chronic running injury sites. Med Sci Sports Exer. June 1990;22(3):357-369.

Cited By (6)

Year	Entry
2016	Morales-Orcajo E, Bayod J, Barbosa de Las Casas E. Computational foot modeling: scope and applications. Arch Comput Methods Eng. September 2016;23(3):389-416.
2023	Finni T, Vanwanseele B. Towards modern understanding of the Achilles tendon properties in human movement research. J Biomech. May 2023;152:111583.
2021	Firminger CR. Experimental Measurement and Applied Modelling of Patellar Tendon Strain [PhD thesis]. Calgary, AB: University of Calgary; May 2021.
2015	Rooney SI. Adaptations of the Supraspinatus Tendon and Muscle in a Rat Model of Exercise [PhD thesis]. Philadelphia, PA: University of Pennsylvania; 2015.
2014	Slane LC. Achilles Tendon Elasticity and Deformation Patterns in Young and Middle-Aged Adults Evaluated Using Quantitative Ultrasound Approaches [PhD thesis]. University of Wisconsin – Madison; 2014.
2015	Mittnacht J. Characterization of Tendon Loading Mechanisms: Shear Loading At Different Hierarchical Levels [PhD thesis]. University of Wisconsin – Madison; 2015.