The effects of refreezing on the viscoelastic and tensile properties of ligaments.

Biomechanical testing protocols for ligaments can be extensive and span two or more days. During this time, a specimen may have to undergo more than one cycle of freezing and thawing. Thus, the objective of this study was to evaluate the effects of refreezing on the viscoelastic and tensile properties of ligaments. The femur-medial collateral ligament-tibia complexes (FMTC) from six pairs of rabbit knees were used for this study. Following sacrifice, one leg in each pair was assigned to the fresh group and the FMTC was immediately dissected and prepared for testing. The contralateral knees were fresh-frozen at -20 degrees C for 3 weeks, thawed, dissected and then refrozen for one additional week before being tested as the refrozen group. The cross-sectional area and shape of the medial collateral ligament (MCL) was measured using a laser micrometer system. Stress relaxation and cyclic stress-relaxation tests in uniaxial tension were performed followed by a load to failure test. When the viscoelastic behavior of the MCL was described by the quasi-linear viscoelastic (QLV) theory, no statistically significant differences could be detected for the five constants (A, B, C, tau1, and tau2) between the fresh and refrozen groups (p > or = 0.07) based on our sample size. In addition, the structural properties of the FMTCs and the mechanical properties of the MCLs were also found to be similar between the two groups (p > or = 0.68). These results suggest that careful refreezing of the specimens had little or no effect on the biomechanical properties measured.