EFFECTS OF ANTIORTHOSTATIC KINESIA ON SPRAGUE DAWLEY RAT FEMUR FRACTURE TOUGHNESS AND CONCOMITANT ALTERATIONS IN METABOLIC ACTIVITY

An antiorthostatic (suspended) rat model was used to assess the effects of disuse on the fracture toughness, K(,1c), of the cortical diaphysis of Sprague-Dawley rat femur. Concomitant metabolic data, e.g. dietary mineral balances and blood chemistry, were used to compare the model to previously published data. It was determined that 28 days of kinetic antiorthostasis results in no significant changes in fracture toughness, although there did appear to be qualitative changes in bone architecture. Further, the metabolic data indicated that the rat maintained a positive calcium balance throughout the study with increased intestinal absorption. The absence of alterations in the femur fracture toughness and the unexpected calcium balance trends were attributed to the kinesia of the animal. Data from the antiorthostatic kinetic (AOK) animal used in this study is compared to that obtained from hypokinetic and immobilized animals. It was concluded that changes in bone growth and remodeling due to disuse or removal of gravitational loads should be approached from a systems point of view with particular emphasis on the relationship(s) between bone blood flow and muscular activity.