AN EVALUATION OF THE NON-LINEAR VISCOELASTIC PROPERTIES OF THE HEALING MEDIAL COLLATERAL LIGAMENT

Injuries to knee ligaments are frequent, demanding an increased understanding of the healing process. Clinically, the injured medial collateral ligament (MCL) has been found to heal without surgical intervention. However, laboratory studies have shown that, even one year after injury, the biomechanical properties, biochemical composition, and histomorphological appearance of the healing MCL remains suboptimal. While research has focused on the changes in mechanical properties (i.e. stress-strain behavior) of the healed MCL, studies on its viscoelastic properties are limited. Yet, this knowledge is critical to determine the overall kinetic response of the knee joint.The quasi-linear viscoelastic (QLV) theory proposed by Professor Y.C. Fung has been frequently used to model the viscoelastic properties of the MCL. This theory was developed based on an idealized step-elongation during a stress relaxation test. As this is experimentally impossible, the constants of the theory may not be representative when they are determine based on experiments that utilize finite strain rates. Thus, the overall objectives of this dissertation were to 1) develop and validate a novel experimental and analytical approach that accounts for finite strain rates and provides an accurate determination of the viscoelastic properties of the normal MCL, 2) apply this new approach to describe the viscoelastic behavior of the healing MCL, and 3) to determine whether the new approach can describe the response of the MCL to harmonic oscillations.This work demonstrated that a newly developed approach could be utilized to determine the constants of the quasi-linear viscoelastic theory and successfully describe the viscoelastic behavior of both the normal and healing MCLs. Interestingly, the healing ligaments display a lower initial slope of the stress-strain curve and a greater propensity to dissipate energy, suggesting other structures within the knee would have to play a compensatory role in knee function. It was also found that the mechanisms governing the viscoelastic response of the MCL to harmonic oscillations may not be the same as that which governs stress relaxation behavior. Thus, a more general theory may be necessary to describe both phenomena