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brao69
03-29-2007, 11:56 PM
Dear all,

Sorry about the delay. Here are the list of responses and my question on what is meant by interspecimen variability.


1)
Interspecimen variability in cadaveric specimens refers to the fact that
people come in all shapes and sizes. Specimens from younger males are
larger and stronger than specimens from older females for example. It
is especially important when performing biomechanical studies on human
cadaveric specimens to try to randomize the specimens between groups,
use matched pairs if there are two groups to be studied, or to group
specimens according to some surrogate measure of strength such as bone
mineral density (using DXA for example). Certain animal species have
less variability because the animals are specifically bred to decrease
the genetic differences (such as certain rat strains). However, using
spinal specimens from "mongrel dogs" will not result in less variability
due to the diversity present across dog strains. (beagle vs german
shepherd for example)


2)
Following are likely causes:

Since each human has a different body structure, so is their spine. This is the prime reason for the variability in cadaver specimens. Also, diseases at different stages alter the mechanical response of the cadaver specimens . The third reason for inter specimen variability is the method of storing (use of preserving chemicals alter mechanical performance); different concentrations of preservatives and different types of preservation techniques will alter the specimen performance. Amount of time the frozen specimen is in storage before testing. Amount of time between death and freezing the specimen. There could be reasons which lead to variability due to combination of the above factors, e.g., since the spine size is different for different specimens, each specimen will have a different loading pattern due to a different placement in the mechanical testing jig.

Regards,
Brunda Rao Kattekola
Engineer, TSI



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