EFFECTS OF FREEZE THAW CONDITIONING ON THE TENSILE PROPERTIES AND FAILURE MODE OF BONE-MUSCLE-BONE UNITS - A BIOMECHANICAL AND HISTOLOGICALSTUDY IN DOGS/

Eight pairs of canine supraspinatus bone-muscle-bone units were mechan ically tested to failure in tension. One side was tested immediately p ost mortem, and the other side was tested after exposure to a standard freeze/thaw process (-60 degrees C). The failure site was analyzed hi stologically. Fresh specimens had greater values for ultimate strength (p < 0.001), stiffness (p < 0.001), and energy to failure (p < 0.001) . All specimens failed in the muscle close to the musculotendinous jun ction. The length of muscles subjected to the freezing process was red uced (9.3%). In addition, the load-displacement curves for the fresh a nd frozen specimens showed marked differences in shape. The loss of te nsile strength in muscle tissue is due to damage of the intracellular contractile elements caused by postmortem autolysis; this type of dama ge is increased as a result of the freeze/thaw process. The freeze/tha w process significantly altered the tensile properties of normal muscl e tissue, no matter how carefully it was done. One cannot expect to re ceive representative data if muscle is frozen and thawed.