Short term cortical bone remodeling in the canine femur as a result of hyperphysiological stresses
Description
This research involves an investigation of the changes in morphology and stiffness of cortical bone as a result of a quantifiable increase in compressive stress. Static compressive loads between zero and one hundred fifty-five Newtons were superposed on the normal loading of both femora of adult mongrel dogs by surgically implanting spring devices in the hindlimbs. The devices consisted of springs which were extended along the length of the diaphysis and attached to pins implanted through the metaphyses. Tetracycline was administered one month after surgery to provide a temporal mark on the bone deposition. The animals were sacrificed two months after the devices were implanted. In order to determine a volume-averaged elastic modulus for the hyperphysiologically stressed bone, a thirty-two millimeter section of the diaphysis was subjected to compression testing in the wet condition within the elastic region of the tissue. These specimens were then plasticized and sectioned Quantitative examinations of both unstained sections, under ultraviolet light, and stained sections were conducted in order to determine the geometric properties of tissue. The examinations included determinations of changes in gross cross-sectional area after one and two months, net cross-sectional area after two months and area moment of inertia The mechanical testing revealed a weak negative linear correlation between the volume-averaged mudulus of elasticity and the superposed stress. The gross and net cross-sectional area increased both displayed positive linear correlations with superposed stress. These were confirmed by an F test for p < 0.05. The gross area was found to increase very little after the first month of load superposition. This slowing of gross area increase and the evidence from the tetracycline labeling of deposition of bone within the matrix deposited in the first month suggests that surface remodeling occurs in two phases. The initial reaction is a rapid but microstructurally disorganized response that results in a significant increase in bony cross-sectional area. The second step is the reorganizing and filling in of newly deposited matrix The findings of this study were used to estimate remodeling rate coefficients for the endosteal and periosteal surface of C(,c) = 0 and C(,p) = 5.5 x 10('-3) millimeters per day