Tendon and ligament biomechanics

Tendons and ligaments are dense regular connective tissues that transmit muscle forces and stabilize joints, respectively. Injuries to these tissues result in signicant disability and pain and often require surgical repair for the return of function. Clinical and experimental studies have shown that these tissues heal poorly. Research efforts are therefore under way to enhance healing through rehabilitation, biological, and tissue engineering approaches. In all cases, return of function requires a recapitulation of the biomechanics of the uninjured tendon or ligament. Therefore, an understanding of the mechanical behavior of these tissues is critical. This chapter will review the current understanding of tendon and ligament mechanics. Although strength, toughness, and constitutive response are all important mechanical properties of tendons and ligaments, the primary focus will lie on constitutive descriptions of these tissues. These are divided into two classes. The rst class includes phenomenological approaches involving macroscopic frameworks that, when calibrated to tissue-level experiments, provide predictions for the responses of tissues to loading regimes beyond those used in calibration experiments. The second class includes microstructure-based models that predict constitutive behavior through multiscale structure-function relationships, incorporating nanoscopic and microscopic information such as tissue composition and organization. Features of both classes of models include stress relaxation, energy dissipation, nonlinearity, and the need for careful calibration and validation.