Distraction osteogenesis in the Cbfa-1+/- mouse.

Distraction osteogenesis involves division of a bone and gradually pulling the bone ends apart. This delivers mechanical stimulation to mesenchymal cells in the distraction gap, where new bone is regenerated predominantly by intramembranous ossification. The transcription factor Cbfa1 has been reported to be essential for the differentiation of mesenchymal cells to osteoblasts. In homozygous Cbfa1 knockout mice, both intramembranous and endochondral ossification mechanisms are blocked and no bone formation occurs. In heterozygous Cbfa1 knockout mice, only the cranial bones and the clavicles, which form through intramembranous ossification, fail to develop properly as in the human condition of cleidocranialdysostosis. It has been suggested, therefore, that intramembranous ossification is affected by the absence of one of the paired Cbfa1 genes. We have assessed the potential for intramembranous ossification following distraction osteogenesis in heterozygous Cbfa1 knockout mice. Fourteen skeletally mature male heterozygous mice were used, together with 10 wild-type controls. The tibia was distracted by 0.25 mm twice a day (0.5 mm/day) for 10 days using the half-ring type fixator. Nine mice were kept for a further 28 days to observe the consolidation phase. In four out of five mice of the heterozygous group and in all three wild-type mice, bony fusion within the distraction gap was observed on radiographs. Histological findings were almost the same in the two groups at various stages of the procedure and intramembranous ossification was predominant in both the groups. Despite the inhibition of intramembranous ossification during the foetal development of Cbfa1+/- mice, distraction osteogenesis was as successful as in control mice.

Vascularity in a new model of atrophic nonunion.

Our aim was to develop a clinically relevant model of atrophic nonunion in the rat to test the hypothesis that the vessel density of atrophic nonunion reaches that of normal healing bone, but at a later time-point. Atrophic nonunion is usually attributed to impaired blood supply and is poorly understood. We determined the number of blood vessels at the site of an osteotomy using immunolocalisation techniques in both normally healing bones and in atrophic nonunion. At one week after operation there were significantly fewer blood vessels in the nonunion group than in the healing group. By eight weeks, the number in the atrophic nonunion group had reached the same level as that in the healing group. Our findings suggest that the number of blood vessels in atrophic nonunion reaches the same level as that in healing bone, but at a later time-point. Diminished vascularity within the first three weeks, but not at a later time-point, may prevent fractures from uniting.

Toxic effect of rifampicin on human osteoblast-like cells.

We examined the effects of rifampicin on osteoblast-like cells derived from adult human bone in vitro. Cancellous bone was collected from five different individuals during elective orthopaedic operations and cultured in antibiotic-free media. Total DNA, 3H-thymidine incorporation and alkaline phosphatase (ALP) activity were measured after the cells were cultured for 4 days in media containing concentrations of rifampicin ranging from 0 to 1000 microg/ml. Mean total DNA was decreased at concentrations of 10 microg/ml and above in the cultures obtained from four out of five individuals but these decreases were significant in the cultures from only two individuals. 3H-thymidine incorporation, a more sensitive indicator of change in cell proliferation, and ALP activity were significantly decreased (P < 0.05) in all of the cultures containing 3 and 7 microg/ml, respectively. In the clinical setting, serum concentrations of rifampicin often exceed 10 microg/ml after systemic administration. The present study has shown that rifampicin, at these concentrations, can inhibit the proliferation of osteoblast-like cells in vitro. Further studies should be carried out to assess whether rifampicin is detrimental to the bone repair process in vivo.

A murine model of distraction osteogenesis.

Distraction osteogenesis is both a valuable clinical technique and a useful tool for investigating the basic mechanisms involved in bone tissue regeneration. Here we describe the development of a murine model of this procedure that can be used in transgenic animals to investigate the role of specific genes in tissue regeneration. Ring fixators were applied to the lower leg of 12 normal adult male mice. An osteotomy was made in the diaphysis of the tibia, and 7 days after the operation the bone fragments were distracted by 0.25 mm twice a day for 10 days. Specimens were examined immediately at the end of distraction and after 14-70 days of consolidation. At the end of distraction, the distraction gap was filled with fibroblast-like cells arranged longitudinally. After 14 days of consolidation, there was radiographical evidence of bone formation in the distraction gap and, after 28 days of consolidation, the bone fragments were fused with regenerated bone. By 70 days of consolidation, the regenerated bone had been almost completely remodeled and the intramedullary canal reestablished. This study is the first to report consolidation of the distraction gap with regenerated bone in a murine model of distraction.

Fibrous dysplasia arising from the calcaneus.

A case of an 18-year-old woman with fibrous dysplasia arising in the calcaneus, which is extremely rare, is reported, with the emphasis placed on differential diagnosis from low-grade central osteosarcoma. She had a severe pain in her left ankle after sprain. Plain radiographs showed a radiolucent lesion measuring 6.3 x 2.5 cm with a sclerotic margin in the left calcaneus. CT scans showed a well-defined lytic lesion with disruption of the lateral cortex and an ossification or calcification in its center. On MR imaging, the lesion had isointensities and high intensities on T1 and T2 weighted images, respectively, but its central portions showed lower intensities both on T1 and T2 weighted images. The lesion was enhanced with gadolinium except for the central portions. The specimen obtained by open biopsy consisted of fibrous tissue and foci of irregular woven bone. None of the nuclear atypia, mitoses, longitudinal stream of bone or invasive nature of growth was detected. The diagnosis of fibrous dysplasia was histologically made. The lesion was curetted and packed with autogenous bone chips. No evidence of recurrence was noted postoperatively.