The goal of this work was to define cellular and molecular changes that occur during fracture healing as animals age. We compared the molecular, cellular, and histological progression of skeletal repair in juvenile (4 weeks old), middle-aged (6 months old), and elderly (18 months old) mice at 3, 5, 7, 10, 14, 21, 28, and 35 days post-fracture, using a non-stabilized tibia fracture model. Our histological and molecular analyses demonstrated that there was a sharp decline in fracture healing potential between juvenile and middle-aged animals, while a more subtle decrease in healing potential was apparent between middle-aged and elderly mice. By three days after fracture, chondrocytes expressing Collagen type II, and osteoblasts expressing osteocalcin, were present in calluses of juvenile, but not middle-aged or elderly, mice. At day 5 immature chondrocytes and osteoblasts were observed in calluses of middle-aged and elderly mice. While at this time, chondrocytes in juvenile mice were expressing Collagen type X (ColX) indicating that chondrocyte maturation was already underway. At day 7, chondrocytes expressing ColX were abundant in middle-aged mice while a small domain of ColX-positive chondrocytes were observed in elderly mice. Further, in juvenile and middle-aged mice, but not elderly mice, vascular invasion of the cartilage was underway by day 7. Juvenile mice had replaced nearly all of the cartilage by day 14, while cartilage was still present in the callus of middle-aged mice at day 21 and in elderly mice at day 28. In addition to these delays, histomorphometry revealed that elderly and middle-aged mice formed less bone than juveniles (p<0.001), while cartilage production was unaffected (p>0.22). Collectively, these data suggest that enhancing cell differentiation, improving osteoblast function, and accelerating endochondral ossification may significantly benefit the elderly.

Age affects fracture repair; however, the underlying mechanisms are not well understood. The goal of this study was to assess the effects that age has on vascularization during fracture healing. Tibial fractures were created in juvenile (4-week-old), middle-aged (6-month-old), and elderly (18-month-old) mice. The length density and surface density of blood vessels within fracture calluses were analyzed using stereology at 7 days after fracture. The expression of molecules that regulate vascular invasion of the fracture callus was also compared among the three age groups by immunohistochemistry and in situ hybridization. At 7 days after fracture, juvenile mice had a higher surface density of blood vessels compared to the middle-aged and elderly. Hypoxia-inducible factor-1a protein and transcripts of vascular endothelial growth factor were detected at 3 days postinjury in juvenile but not middle-aged and elderly mice. Stronger Mmp-9 and -13 expression was detected in fracture calluses at day 7 in the juvenile compared to the middle-aged and elderly mice. At 21 days postfracture, expression of both Mmps was more robust in the elderly than juvenile and middle-aged animals. These data indicate that age affects vascularization during fracture repair, and the changes we observed are directly correlated with altered expression of biochemical factors that regulate the process of angiogenesis. However, whether the increased vascularization is the cause or result of accelerated bone repair in juvenile animals remains unknown. Nonetheless, our results indicate that enhancing vascularization during fracture repair in the elderly may provide unique therapeutic opportunities. ß

The re-establishment of vascularity is an early event in fracture healing; upregulation of angiogenesis may therefore promote the formation of bone. We have investigated the capacity of vascular endothelial growth factor (VEGF) to stimulate the formation of bone in an experimental atrophic nonunion model. Three groups of eight rabbits underwent a standard nonunion operation. This was followed by interfragmentary deposition of 100 microg VEGF, carrier alone or autograft. After seven weeks, torsional failure tests and callus size confirmed that VEGF-treated osteotomies had united whereas the carrier-treated osteotomies failed to unite. The biomechanical properties of the groups treated with VEGF and autograft were identical. There was no difference in bone blood flow. We considered that VEGF stimulated the formation of competent bone in an environment deprived of its normal vascularisation and osteoprogenitor cell supply. It could be used to enhance the healing of fractures predisposed to nonunion.

A collaborative, population based, prospective register study on (40/o) in the incidence study. Two thirds of the children had additional impairments and these children also suffered from the most severe visual impairments. Among aetiological factors the majority (64%) were prenatal. The overall male:female ratio of 1-4:1 was identical to the sex ratio ofthe prevalence study.

The goal of this work was to define cellular and molecular changes that occur during fracture healing as animals age. We compared the molecular, cellular, and histological progression of skeletal repair in juvenile (4 weeks old), middle-aged (6 months old), and elderly (18 months old) mice at 3, 5, 7, 10, 14,21,28, and 35 days post-fracture, using a non-stabilized tibia fracturqmodel. Our histological and molecular analyses demonstrated that there was a sharp decline in fracture healing potential between juvenile and middle-aged animals, while a more subtle decrease in healing potential was apparent between middle-aged and elderly mice. By three days after fracture, chondrocytes expressing Collagen type ZZ, and osteoblasts expressing osteocalcin, were present in calluses of juvenile, but not middle-aged or elderly, mice. At day 5 immature chondrocytes and osteoblasts were observed in calluses of middle-aged and elderly mice. While at this time, chondrocytes in juvenile mice were expressing Collagen type X (ColX) indicating that chondrocyte maturation was already underway. At day 7, chondrocytes expressing ColX were abundant in middle-aged mice while a small domain of ColX-positive chondrocytes were observed in elderly mice. Further, in juvenile and middle-aged mice, but not elderly mice, vascular invasion of the cartilage was underway by day 7. Juvenile mice had replaced nearly all of the cartilage by day 14, while cartilage was still present in the callus of middle-aged mice at day 21 and in elderly mice at day 28. In addition to these delays, histomorphometry revealed that elderly and middle-aged mice formed less bone than juveniles (p < 0.001), while cartilage production was unaffected (p > 0.22). Collectively, these data suggest that enhancing cell differentiation, improving osteoblast function, and accelerating endochondral ossification may significantly benefit the elderly.