To clarify the mechanisms underlying shockwave-induced osteogenesis, we applied shockwave to rat femoral shafts from the ventral side. We assessed bone mineral content (BMC) and bone mineral density (BMD), and analyzed the spatial and temporal gene expression for pro-alpha1 (I) collagen (COL1A1), pro-alpha1 (II) collagen (COL2A1), pro-alpha1 (X) collagen (COL10A1), osteocalcin (OC) and osteopontin (OPN) using in situ hybridization. On the 21st day post-exposure, BMC and BMD in the exposed femur were elevated by 8.46% and 5.80%, respectively, relative to the unexposed femur. Immediately following exposure, there was evidence of scraping of the cortex and periosteal separation with hemorrhage. On day 4, new periosteal bone formation could be seen on the ventral and dorsal side of the femur. In the newly formed bone, COL1A1, OC and OPN were expressed in osteoblastic cells underlying the periosteum. On day 7, there was progression of periosteal bone and trabeculae formation. COL1A1 and OC were expressed in mature osteoblasts lining the trabeculae, whereas OPN was expressed in immature osteoblastic cells, osteocytes and osteoclasts. On day 14, bone remodeling commenced in the periosteal bone. COL1A1, OC and OPN were still expressed at this stage, however, signals were much weaker. Between 4-7 days, chondrocyte clusters were distributed multi-focally near the exposed site, and there was expression of COL2A1 but not of COL10A1. The results demonstrate that gene expression patterns of shockwave-induced osteogenesis are similar to those of periosteal hard callus formation during fracture healing. Shockwaves can yield dramatic activation of cells in normal long bones, and drive the cells to express genes for osteogenesis.
Abstract:The Preserve stem is a modified Zweymüller femoral stem that omits the trochanteric wing. Omission of the trochanteric wing of the prosthesis might influence its rotational stability, but, there are no reports about the rotational stability of a modified Zweymüller femoral stem. The purpose of this study was to investigate the effect of the trochanteric wing on rotational stability by comparing the modified Zweymüller femoral stem and the original Zweymüller femoral stem. Computed tomography of the right femur was used to construct a resin model of the proximal femur. Three types of uncemented stems were used in this study: Preserve α, β, and exemplary Zweymüller stem. Preserve β is a modified Zweymüller-type of stem with a reduced trochanteric wing. Preserve α is also a Zweymüller-type of stem with a further reduced trochanteric wing. The resin bone model was mounted on a universal testing machine. The stem was inserted into the bone model manually and loaded vertically up to 600 N. Then the stem was rotated posteriorly by 1°/sec until angular rotation was achieved to 5°. The torque at 5° was compared among the three stems. Vertical displacement of the stem during rotation testing was also recorded as a correlative measure for prosthetic subsidence. The results showed that the mean torque at 5° was not significantly different among the Preserve α, β, and exemplary Zweymüller stem (Tukey-Kramer test). Furthermore, the mean vertical displacement amounts during rotation testing were not significantly different among the three stems (Tukey-Kramer test). This study indicate that the Preserve α and β, modified Zweymüller stems, are rotationally as stable as the exemplary Zweymüller stem.
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