Effect of Hypophysectomy and Estrogen Treatment on Long Bone Fracture Healing of Young Domestic Fowls

NEGULESCO, JOHN A. AND JOHN A. EGLITIS. Effect of hypophysectomy and estrogen treatment on long bone fracture healing of young domestic fowls. Ohio J. Sci. 75(5): 217, 1975. Estrogen treatment stimulates osteoblast proliferation at fracture sites of nonhypophysectomized 2-week-old birds. The hormone antagonizes growth factor of the intact 4-week bird, and induces modulation of subperiosteal osteochondrogenic connective tissue cells. It also limits neovascularization of the fracture site cartilaginous union collar of the 4week old animal. Hypophysectomy with or without estrogen treatment results in fracture site ischaemia which depresses osteogenesis in the 2-week-old bird, and increases cartilage production at 4 weeks post hatching. Hypophysectomy without estrogen treatment decreases maturation and proliferation of connective tissue cellular elements and leads to accumulation of early osteochondrogenic cells at healing fracture sites of 4-week-old birds. The basic problems in fracture healing are the outcome of stimulation, multiplication, differentiation, and proliferation of extra-periosteal, periosteal, and endosteo-medullary connective tissue celular elements. The succession of these events results in the formation of a reparative blastema, callus, and bony union. Each fracture represents an unique study complicated by the nature 'Manuscript received May 13, 1975, revised September 24, 1975 (#75-28)". of its highly pliable and pluri-potential cell population, differing internal environment (blood supply and oxygen tension), and a multitude of superimposing physical factors such as stress, strain, compression, and immobilization (Pritchard, 1964). Osteogenesis within a healing fracture callus was considered by Ham (1930) to depend on the local circulation. Bone develops in a vascularized fracture while cartilage predominates in avascular or poorly penetrated sites. Ideal fracture management was shown by McLean and Urist (1968) to convert the callus to young bone. Less desirable conditions exemplified by unsplintered mobile breaks, or those traumatized by compressive and shearing forces, result in an unpredictable fracture outcome. The initial union, instead of bony may be cartilaginous or fibrous (Cohen and Lacroix, 1955).