Biomedical subjects

Sarah Muchow

Publications and source records attributed to Sarah Muchow.

2 recordsLinked to original sources

PubMed2005

Osteoclastic activity begins early and increases over the course of bone healing.

Osteoclasts are specialised bone-resorbing cells. This particular ability makes osteoclasts irreplaceable for the continual physiological process of bone remodelling as well as for the repair process during bone healing. Whereas the effects of systemic diseases on osteoclasts have been described by many authors, the spatial and temporal distribution of osteoclasts during bone healing seems to be unclear so far. In the present study, healing of a tibial osteotomy under standardised external fixation was examined after 2, 3, 6 and 9 weeks (n = 8) in sheep. The osteoclastic number was counted, the area of mineralised bone tissue was measured histomorphometrically and density of osteoclasts per square millimetre mineralised tissue was calculated. The osteoclastic density in the endosteal region increased, whereas the density in the periosteal region remained relatively constant. The density of osteoclasts within the cortical bone increased slightly over the first 6 weeks, however, there was a more rapid increase between the sixth and ninth weeks. The findings of this study imply that remodelling and resorption take place already in the very early phase of bone healing. The most frequent remodelling process can be found in the periosteal callus, emphasising its role as the main stabiliser. The endosteal space undergoes resorption in order to recanalise the medullary cavity, a process also started in the very early phase of healing at a low level and increasing significantly during healing. The cortical bone adapts in its outward appearance to the surrounding callus structure. This paradoxic loosening is caused by the continually increasing number and density of osteoclasts in the cortical bone ends. This study clearly emphasises the osteoclastic role especially during early bone healing. These cells do not simply resorb bone but participate in a fine adjusted system with the bone-producing osteoblasts in order to maintain and improve the structural strength of bone tissue.

Animals↗

PubMed2005

Initial vascularization and tissue differentiation are influenced by fixation stability.

Fracture healing requires a certain degree of mechanical stability and an adequate blood supply. The hypothesis of the present study was that increased interfragmentary shear leads to a reduced initial vascularization and prolonged healing. The aim of the study was to quantitatively analyze the histological appearance of vascularization and tissue differentiation with regard to fracture stability during the course of healing. A mid-shaft osteotomy of the tibia was performed in two groups of sheep and stabilized with either a rigid or semirigid external fixator, differing in bending stiffness. Interfragmentary movements and ground reaction forces were evaluated in vivo during a 9-week period. The sheep were sacrificed at 2, 3, 6, and 9 weeks postoperatively. The tibiae were tested biomechanically and histological sections from the callus were prepared for analysis of tissue differentiation and vascularization. Larger interfragmentary shear movements in the semirigid fixator group were associated with a reduced initial blood supply. At 6 weeks the semirigid fixator group showed a significantly lower percentage of mineralized bone and a higher amount of fibrous tissue leading to a significantly lower stiffness of the callus than the rigid fixator group. This initial delay in healing was compensated for in the later stages with the production of greater volumes of callus tissue so that both groups showed the same callus stiffness at 9 weeks. However, the rigid fixator group showed signs of the beginning of callus remodeling at the latest time points suggesting a faster bone healing. The results indicate the important role of the initial mechanical stability specifically in the vascularization of an osteosynthesis. Further studies should illustrate the precise role of mechanical conditions on the regulation of angiogenesis during early bone healing.

Animals↗