Summary
As orthopaedic investigations have become more intricate, bone specimens have sometimes
undergone multiple freeze-thaw cycles prior to biomechanical testing. The purpose
of this study was to determine if repeated freezing and thawing affected the mechanical
properties of canine cortical bone. Six pairs of third-metacarpal bones were tested
in three-point bending and six pairs of femurs were tested in torsion. At the time
of collection, one member of each pair was tested destructively. The other member
was tested nondestructively at the time of collection and after each of five freeze-thaw
cycles, followed by destructive testing after the fifth cycle. For destructive tests,
the material properties (modulus, maximum stress, maximum strain and absorbed energy)
of a specimen at the time of collection were compared to those of the corresponding
contralateral specimen that had undergone five freeze-thaw cycles. For repeated nondestructive
tests, the modulus of a specimen at the time of collection was compared to modulus
of the same specimen at each of the five thaw intervals. During destructive testing,
there was a significant (p = 0.02) decrease (20%) in maximum torsional strain. Other
changes in bending and torsional destructive properties were not statistically significant.
During repeated nondestructive testing, there were solitary significant (p < 0.05)
increases (8% and 9%, respectively) in both bending and torsional modulus. However,
these isolated changes were not correlated to the number of freeze-thaw cycles. The
pattern of alterations in destructive and non-destructive biomechanical properties
was most consistent with varying specimen dehydration at each thaw interval. Despite
using accepted methods to maintain specimen hydration, repeated freezing, thawing,
handling and testing of cortical bone increased the risk of moisture loss. Unless
stringent efforts are made to ensure proper hydration, the mechanical properties of
canine cortical bone will be altered by repeated freezing and thawing, affecting the
results of studies utilizing this technique.
The effect of five freeze-thaw cycles on paired canine cortical bone specimens was
evaluated using destructive and repeated non-destructive three-point bending and torsion
tests. A significant decrease in destructive torsional strain and isolated significant
increases in nondestructive bending and torsional modulus were most consistent with
varying specimen dehydration at each thaw interval.
Keywords
Biomechanical testing - cortical bone - repeated freezing - dog
