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.

Fixed membranous bone graft survival after recipient bed alteration.

The effectiveness of membranous bone grafting in craniofacial reconstruction is hindered by resorption. The aim of this study was to determine whether alterations of the recipient bed through tissue expansion affect membranous bone graft survival. Eighteen adult rabbits were divided into three groups. Group I rabbits (control) received fixed autologous membranous bone grafts to their snouts. Group II rabbits had self-inflating tissue expanders inserted over their nasal dorsum, inflation for 3 weeks, and then expander removal and placement of fixed autologous membranous bone grafts to their snouts. Group III rabbits varied from group II by delaying bone grafting until 2 weeks after expander removal. One animal from each group was killed at post-grafting days 15 and 45, the remainder at day 90. Results were assessed by volumetric, nondecalcified histologic, and stereologic analysis. Volumetrically, group I grafts demonstrated 82 percent survival, whereas group II demonstrated 101 percent (p = 0.029) and group III 94.5 percent (p = 0.21). Histologically, group I grafts exhibited greater loss (i.e., porosity and resorption) and less labeling activity. Groups II and III showed extensive evidence of trabecularization and incorporation at the graft-host interface. Stereologic measurements such as osteoid seam width (OSW) confirmed the greater survival and activity of groups II and III bone grafts. Group II OSW measured 12.4 microns, group III 12.0 microns, and group I 9.8 microns (p = 0.04). Stereology also demonstrated that groups II and III's OSW approached that of the recipient bed and contralateral zygoma, whereas group I did not (p = 0.029), suggesting an integration of the graft and host architectures.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of intraosseous infusion on the growth plate in a nestling rabbit model.

STUDY OBJECTIVE: The objective of this study was to test the hypothesis that saline or bicarbonate infusion does not damage the growth plate in a nestling rabbit model. SETTING: Animal laboratory. DESIGN: In this prospective study, 22 tibias from nestling rabbits were randomized into control, puncture-only, physiologic saline, or bicarbonate infusion groups and killed three and five days after treatment for evaluation of injury. MEASUREMENTS: Bone injury was evaluated by microradiograph and by decalcified and undecalcified histology. RESULTS: Radiographs demonstrated loss of trabecular (ie, calcified) bone after infusion of both saline and bicarbonate solutions. Although no histologic damage to the cell lines of the growth plate was seen, newly formed bone trabeculae were seen in both infusion groups, suggesting injury and repair at sites of infusion. These findings were absent in control and puncture-only groups. No histologic or radiographic differences were seen between saline and bicarbonate infusions. CONCLUSION: The nestling rabbit provides a good animal model for evaluating the effects of intraosseous infusion on growing long bones and cartilage. Saline and bicarbonate infusions did not damage morphologically the metaphyseal growth plate but did cause loss of bone trabeculae that support the growth plate. The injury appeared to be repaired rapidly in these nestling rabbits.