Short communication
The effects of refreezing on the viscoelastic and tensile properties of ligaments

https://doi.org/10.1016/j.jbiomech.2005.02.012Get rights and content

Abstract

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 °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, τ1, and τ2) between the fresh and refrozen groups (p0.07) 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 (p0.68). These results suggest that careful refreezing of the specimens had little or no effect on the biomechanical properties measured.

Introduction

Fresh frozen soft tissues are normally used for biomechanics research. However, as experimental protocols for biomechanical evaluation are becoming more complex and time-consuming, specimens may require extra periods of frozen storage before the experiment is completed (Shoemaker and Markolf, 1982). Although one period of frozen storage on ligaments has been shown to have relatively little effect on the biomechanical properties of ligaments (Viidik and Lewin, 1966; Noyes and Grood, 1976; Dorlot et al., 1980; Barad et al., 1982; Nikolaou et al., 1986; Woo et al., 1986) and tendons (Matthews and Ellis, 1968; Leitschuh et al., 1996; Clavert et al., 2001), it is unclear if refreezing will significantly affect these properties.

Therefore, the objective of this study was to evaluate the effects of refreezing on ligaments, specifically on the viscoelastic and structural properties of the femur-medial collateral ligament-tibia complex (FMTC), as well as the mechanical properties of the medial collateral ligament (MCL) midsubstance in comparison to fresh specimens. In addition, the preparation used for the refrozen specimen was a regimen designed to mimic the laboratory setting where a frozen/thawed ligament may be completely exposed during dissection and testing before it is refrozen. Since one cycle of freezing and thawing was previously found to affect the area of hysteresis in the previous study (Woo et al., 1986), a more robust viscoelastic analysis was performed in this study.

Section snippets

Materials and methods

Six pairs of knees from skeletally mature female New Zealand white rabbits (body mass=5.0±0.5 kg) were used. All animal procedures were done in compliance with the National Institutes of Health guidelines for animal care and the Institutional Animal Care and Use Committee (IACUC). One knee in each pair was assigned to the fresh group. These specimens were dissected down to the FMTC and prepared for testing immediately after sacrifice. Knees in the refrozen group were wrapped in saline soaked

Results

No differences in the gross appearance of the tissues could be discerned as all specimens appeared shiny, white, and opaque, with well-defined edges. In addition, no significant differences were detected in the cross-sectional areas between the fresh group (4.0±0.6mm2) and the refrozen group (4.1±0.6mm2;p=0.66;β=0.92).

The peak strains for the static stress-relaxation test were 4.2±0.3% and 4.1±1.1% with peak stresses of 28.5±5.2 and 28.0±6.9 MPa, respectively, for the fresh and refrozen groups.

Discussion

In this study, the effects of refreezing on the viscoelastic and structural properties of the FMTC in addition to the mechanical properties of the MCL were evaluated. This study is uniquely different from the previous studies looking at the effects of freezing (Viidik and Lewin, 1966; Noyes and Grood, 1976; Dorlot et al., 1980; Barad et al., 1982; Nikolaou et al., 1986; Woo et al., 1986), in that the specimen was frozen and thawed twice. Further, the ligament was dissected and exposed before

Acknowledgment

The authors acknowledge the financial support provided by the National Institute of Health Grant AR41820.

References (18)

There are more references available in the full text version of this article.

Cited by (143)

  • Ligaments

    2022, Foot and Ankle Biomechanics
View all citing articles on Scopus
View full text