Short communicationThe effects of refreezing on the viscoelastic and tensile properties of ligaments
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 and the refrozen group .
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.
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