title: A comparison of the quasi-static mechanical and non-linear viscoelastic properties of the human semitendinosus and gracilis tendons.
abstract: BACKGROUND
  Over 50-% of anterior cruciate ligament reconstructions are performed using semitendinosus and gracilis tendon autografts. Despite their increased use, there remains little quantitative data on their mechanical behavior. Therefore, the objective of this study was to investigate the quasi-static mechanical and non-linear viscoelastic properties of human semitendinosus and gracilis tendons, as well as the variation of these properties along their length.
  
  
  METHODS
  Specimens were subjected to a series of uniaxial tensile tests: 1-h static stress-relaxation test, 30 cycle cyclic stress-relaxation test and load to failure test. To describe the non-linear viscoelastic behavior, the quasi-linear viscoelastic theory was utilized to model data from the static stress-relaxation experiment.
  
  
  RESULTS
  The constants describing the viscoelastic behavior were similar between the proximal and distal halves of the gracilis tendon. The proximal half of the semitendinosus tendon, however, had a greater viscous response than its distal half, which was also significantly higher than the proximal gracilis tendon. In terms of the quasi-static mechanical properties, the properties were similar between the proximal and distal halves of the semitendinosus tendon. However, the distal gracilis tendon showed a significantly higher tangent modulus and ultimate stress compared to its proximal half, which was also significantly higher than the distal semitendinosus tendon.
  
  
  CONCLUSIONS
  The results of this study demonstrate differences between the semitendinosus and gracilis tendons in terms of their quasi-static mechanical and non-linear viscoelastic properties. These results are important for establishing surgical preconditioning protocols and graft selection.
authors.affiliation: Musculoskeletal Research Center, Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States. sabram@engr.pitt.edu
authors.forename: Steven D
authors.initials: SD
authors.lastname: Abramowitch
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Zhang
authors.forename: Molly
authors.initials: M
authors.lastname: Curran
authors.forename: Robert
authors.initials: R
authors.lastname: Kilger
mesh_terms: D002102:Cadaver; D003198:Computer Simulation; D055119:Elastic Modulus / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D017711:Nonlinear Dynamics; D013314:Stress, Mechanical; D013710:Tendons / Q000502:physiology*; D014783:Viscosity