Skeletal changes in the ovariectomised ewe and subsequent response to treatment with 17 beta oestradiol.

The ewe has been suggested as a suitable large animal model for assessment of therapeutic agents for the treatment of osteoporosis. In this study we asses the response of ewe bone mineral parameters, using dual energy x ray absorptiometry (DXA), after ovariectomy. Regular DXA analysis was performed over a period of 75 weeks followed by a period of dosing with 17 beta oestradiol. Total body bone mineral density (BMD) was reduced in ovariectomised animals 15 weeks post operatively. BMD remained lower than control animals for the entire pre dose period. Subsequently, dosing with 17 beta oestradiol prevented further loss of bone over a period of 38 weeks. Several complicating factors were noted during the study including seasonal BMD variation, a correlation between fat/lean ratio and total body BMD together with a reversible reduction in bone mineral content as a result of lactation. Also changes in BMD were associated with age at ovariectomy.

The influence of bony architecture on fixed membranous bone graft survival.

The aim of this study was to examine the influence of membranous bone graft architecture on graft survival. Eighteen adult New Zealand rabbits underwent full-thickness harvesting of their zygoma, which was then divided into two parts, resulting in a wider, thicker anterior graft and a tapered posterior graft. The grafts were then rigidly fixed, one to each nasal bone, using titanium lag screws. On postgrafting days 15 and 45, 3 animals each were killed. The remaining 12 animals were killed on day 90. The graft, graft-host interface, and contralateral zygoma were assessed volumetrically, histologically (nondecalcified), and stereologically. Volumetrically, the anterior (thicker, wider) grafts demonstrated 100% survival while the posterior (thinner, more narrow) grafts demonstrated 80% survival (p = 0.004). Histologically, the anterior grafts demonstrated less resorption and porosity and greater labeling activity. At the graft-host interface, the anterior grafts exhibited a 2.5-fold increase in full incorporation of the grafts, and the posterior grafts had almost twice the incidence of nonincorporation. Stereological measurements, including interlabel width (20.3 microns anteriorly, 18.9 microns posteriorly), confirmed the enhanced survival of the anterior grafts. Using multiple forms of analyses, this study demonstrates that membranous bone graft architecture influences graft survival. To assist in understanding these differences, we also analyzed the normal contralateral zygoma. While the anterior and posterior halves had a relatively constant amount of bicortical bone, the thicker grafts had a proportionally greater trabecular component (i.e., increased diploë-to-cortical ratio). In the rabbit model, differences in membranous bone thickness imply differences in the cancellous portion of the graft, thereby influencing ultimate graft survival.