The object of the proposed research is to continue to investigate the stimulation of fracture healing with a capacitively coupled electrical field and to determine the mechanisms of action of electrically induced osteogenesis. The proposed research is designed 1) to determine the most efficient duty cycle in applying a capacitively coupled electrical signal to stimulate fracture healing in are osteotomized rabbit fibula model, and 2) to determine the mechanism(s) fo electrically induced osteogenesis by evaluating a) the microenvironmental changes (p0/2, pH) occurring in the vicinity of a cathode, b) possible responding cells (bone cell, capillary endothelial cell, pericyte, and polymorphic cells), and c) intracellular calcium, cyclic AMP, and prostaglanin (PGE2). Methods to be used include histologic, roentgenographic, and mechanical testing of osteotomized rabbit fibula; mathematic modeling using finite element analysis to calculate electric fields in rabbit fibula callus; microscopic morphologic digitablization (Zeiss MOP-3) of newly formed bone in the vicinity of a cathode in the rabbit tibial medullary canal; needle electrode determination of p0/2 and pH of medullary canal in the vicinity of an active cathode; Coulter cell counting, S35 and C14proline uptake, and collagen typing of isolated rat calvarial bone cells, calf brain capillary endothelial cells and pericytes, and rabbit tibia post-traumatic polymorphic cells exposed to various capacitively coupled electrical fields; histologic examination and collagen content and typing of bone cells, endothelial cells, pericytes, and polymorphics grown in Algire diffusion chambers placed within the rabbit tibia medullary canal and exposed to direct current; electron microscopic evaluation of the role of the polymorphic cell as an osteoblast precursor cell and of the role of the endothelial cell and pericyte as possible origins of the polymorphic cell and correlating these findings with histologic staining for factor VIII, antismooth muscle actin antibody, and for alkaline phosphatase; cAMP, prostaglandin, and intracellular ionized calcium changes induced by an electric field; and Fura 2 fluorescence and quantitative digitized fluorescent microscopy to determine the relationship of chondrocyte intracellular calcium to matrix mineralization in the fracture callus.