Guidelines for ex vivo mechanical testing of tendon

Abstract

Tendons are critical for the biomechanical function of joints. Tendons connect muscles to bones and allow for the transmission of muscle forces to facilitate joint motion. Therefore, characterizing the tensile mechanical properties of tendons is important for the assessment of functional tendon health and efficacy of treatments for acute and chronic injuries. In this guidelines paper, we review methodological considerations, testing protocols, and key outcome measures for mechanical testing of tendons. The goal of the paper is to present a simple set of guidelines to the nonexpert seeking to perform tendon mechanical tests. The suggested approaches provide rigorous and consistent methodologies for standardized biomechanical characterization of tendon and reporting requirements across laboratories.

Keywords: biomechanics; tendon.

FIGURE 1

Representative mechanical behavior of two commonly used animal model tendons under uniaxial tension (superficial digital flexor tendon, SDFT, tail fascicle, TF). To describe the material properties, stress (σ) is plotted against strain (ε), after normalization according to tissue dimensions. The curve is annotated to show important behaviors that are interpreted in Table 1. A–B represent the toe region and B–E represent the elastic region of the loading curve. The stress at E represents the yield point, or the onset of “failure in continuity.” The maximum stress at F represents the ultimate strength or failure stress. G represent the point at which the tissue loses its continuity and load bearing capacity. The modulus is determined as the slope of σ- ε curve in the elastic region within the physiological strain range. The area under the curve between point A–F represents the energy to failure, which can be interpreted as the toughness of the tissue. Note that this curve will differently scale depending on the material properties of the load-bearing collagen matrix and multiscale collagen structure of the particular tendon being tested.