The aim of this study was to characterize the effect of ligament water content on the accumulation of damage in vitro. MCLs of the rabbit knee were subjected to a constant cyclic stress for twenty-four hours (isotonic or hypotonic solution) and then failed. Ligaments cycled in hypotonic solution at 0.1 Hz demonstrated significantly more cyclic strain during loading and had significant reductions in both failure stress and failure strain. This study has demonstrated that elevated tissue water content influences the accumulation of damage in ligaments subjected to repetitive loading in vitro, leading to reductions in both strength and failure strain.

Ligament water content may be altered in vivo during activity, following injury or during surgical intervention; tissue hydration can also be manipulated during in vitro testing. Currently, the effect of ligament water content on the accumulation of damage with loading is unknown. The aim of this study was to characterize the effect of ligament water content on the accumulation of damage during in vitro mechanical testing. We hypothesized that Medial Collateral Ligaments (MCL) subjected to repetitive stress under hypotonic conditions would accumulate more damage than ligaments loaded in an isotonic environment.

MCLs of the rabbit knee were subjected to a constant cyclic stress (28 MPa) in this ex vivo model of loading. Tissues were bathed in either an isotonic or hypotonic solution (10% or 0.1% Sucrose) and were cycled at one of two frequencies (1 Hz or 0.1 Hz) for 24 hours followed by failure testing.

After twenty-four hours of loading, ligaments cycled in hypotonic solution at 0.1 Hz had statistically significant reductions in both failure stress and failure strain. This group also demonstrated significantly more cyclic strain during loading than MCLs cycled in isotonic solution. Surprisingly, a significant difference in cyclic modulus was not detected between groups.

This study has demonstrated that elevated tissue water content influences the accumulation of damage in ligaments subjected to repetitive loading in vitro, leading to reductions in both strength and failure strain. The interaction between tissue water content, cyclic strain and tissue damage will be the focus of further study.