title: Digital image correlation as a tool for three-dimensional strain analysis in human tendon tissue.
abstract: BACKGROUND
  Determining the mechanical behaviour of tendon and ligamentous tissue remains challenging, as it is anisotropic, non-linear and inhomogeneous in nature.
  
  
  METHODS
  In this study, three-dimensional (3D) digital image correlation (DIC) was adopted to examine the strain distribution in the human Achilles tendon. Therefore, 6 fresh frozen human Achilles tendon specimens were mounted in a custom made rig for uni-axial loading. 3D DIC measurements of each loading position were obtained and compared to 2 linear variable differential transformers (LVDT's).
  
  
  RESULTS
  3D DIC was able to calculate tendon strain in every region of all obtained images. The scatter was found to be low in all specimens and comparable to that obtained in steel applications. The accuracy of the 3D DIC measurement was higher in the centre of the specimen where scatter values around 0.03% strain were obtained. The overall scatter remained below 0.3% in all specimens. The spatial resolution of 3D DIC on human tendon tissue was found to be 0.1 mm(2). The correlation coefficient between the 3D DIC measurements and the LVDT measurements showed an excellent linear agreement in all specimens (R(2) = 0.99). Apart from the longitudinal strain component, an important transverse strain component was revealed in all specimens. The strain distribution of both components was of a strongly inhomogeneous nature, both within the same specimen and amongst different specimens.
  
  
  CONCLUSIONS
  DIC proved to be a very accurate and reproducible tool for 3D strain analysis in human tendon tissue.
authors.affiliation: Department of Orthopaedic Surgery & Traumatology, University Hospitals Leuven, Weligerveld 1, Pellenberg, 3212, Belgium. luyckx.thomas@gmail.com.
authors.forename: Thomas
authors.initials: T
authors.lastname: Luyckx
authors.affiliation: Department of Orthopaedic Surgery & Traumatology, University Hospital Gent, Gent, Belgium. matthias.verstraete@ugent.be.|Department of Mechanical Construction and Production, University of Gent, Gent, Belgium. matthias.verstraete@ugent.be.
authors.forename: Matthias
authors.initials: M
authors.lastname: Verstraete
authors.affiliation: Department of Orthopaedic Surgery & Traumatology, University Hospital Gent, Gent, Belgium. karelderoo@gmail.com.
authors.forename: Karel
authors.initials: K
authors.lastname: De Roo
authors.affiliation: Department of Mechanical Construction and Production, University of Gent, Gent, Belgium. wim.dewaele@ugent.be.
authors.forename: Wim
authors.initials: W
authors.lastname: De Waele
authors.affiliation: Department of Orthopaedic Surgery & Traumatology, Ziekenhuis Oost Limburg, Genk, Belgium. johan.bellemans@skynet.be.
authors.forename: Johan
authors.initials: J
authors.lastname: Bellemans
authors.affiliation: Department of Orthopaedic Surgery & Traumatology, University Hospital Gent, Gent, Belgium. jan.victor@uzgent.be.
authors.forename: Jan
authors.initials: J
authors.lastname: Victor
keywords: Achilles tendon; Digital image correlation; Strain analysis