title: Shear load transfer in high and low stress tendons.
abstract: BACKGROUND
  Tendon is an integral part of joint movement and stability, as it functions to transmit load from muscle to bone. It has an anisotropic, fibrous hierarchical structure that is generally loaded in the direction of its fibers/fascicles. Internal load distributions are altered when joint motion rotates an insertion site or when local damage disrupts fibers/fascicles, potentially causing inter-fiber (or inter-fascicular) shear. Tendons with different microstructures (helical versus linear) may redistribute loads differently.
  
  
  METHODS
  This study explored how shear redistributes axial loads in rat tail tendon (low stress tendons with linear microstructure) and porcine flexor tendon (high stress with helical microstructure) by creating lacerations on opposite sides of the tendon, ranging from about 20% to 60% of the tendon width, to create various magnitudes of shear. Differences in fascicular orientation were quantified using polarized light microscopy.
  
  
  CONCLUSIONS
  Unexpectedly, both tendon types maintained about 20% of pre-laceration stress values after overlapping cuts of 60% of tendon width (no intact fibers end to end) suggesting that shear stress transfer can contribute more to overall tendon strength and stiffness than previously reported. All structural parameters for both tendon types decreased linearly with increasing laceration depth. The tail tendon had a more rapid decline in post-laceration elastic stress and modulus parameters as well as a more linear and less tightly packed fascicular structure, suggesting that positional tendons may be less well suited to redistribute loads via a shear mechanism.
authors.affiliation: Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, WI 53705, USA; Department of Orthopedics and Rehabilitation, University of Wisconsin-Madison, Madison, WI 53705, USA.
authors.forename: Jaclyn
authors.initials: J
authors.lastname: Kondratko-Mittnacht
authors.affiliation: Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, WI 53705, USA; Department of Orthopedics and Rehabilitation, University of Wisconsin-Madison, Madison, WI 53705, USA.
authors.forename: Sarah
authors.initials: S
authors.lastname: Duenwald-Kuehl
authors.affiliation: Materials Science Program, University of Wisconsin-Madison, Madison, WI 53705, USA; Department of Engineering Physics, University of Wisconsin-Madison, Madison, WI 53705, USA.
authors.forename: Roderic
authors.initials: R
authors.lastname: Lakes
authors.affiliation: Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, WI 53705, USA; Department of Orthopedics and Rehabilitation, University of Wisconsin-Madison, Madison, WI 53705, USA; Materials Science Program, University of Wisconsin-Madison, Madison, WI 53705, USA. Electronic address: vanderby@ortho.wisc.edu.
authors.forename: Ray
authors.initials: R
authors.lastname: Vanderby
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D008422:Materials Testing; D057054:Molecular Imaging; D051381:Rats; D013314:Stress, Mechanical; D013552:Swine; D013710:Tendons / Q000166:cytology / Q000502:physiology*; D016474:Weight-Bearing
keywords: Shear; Structure; Tendon; Tendon function; Viscoelasticity