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1.
Developmental dysplasia of the hip (DDH) is the most common orthopedic problem of newborn children. Most clinicians and researchers agree that the primary cause of DDH is abnormal mechanical forces on the head of the femur due to limb position, pressure from the womb, or ligament laxity. The abnormal mechanical forces result in altered growth and bony deformities, in particular large neck-shaft and anteversion angles in the proximal femur and a shallow acetabulum. Previous studies have suggested that intermittent octahedral shear stress promotes growth and ossification, while intermittent hydrostatic compressive stress inhibits growth and ossification. We implemented these mechanobiological principles into a finite element model to predict the rate of progression of the growth front and the formation of coxa valga (large neck-shaft angle) in DDH. Under the assumed normal fetal loading conditions the hydrostatic stress was even across the growth front, but the octahedral shear stress was higher in the center than at the edges. This stress profile promoted growth in the center and a produced a convex growth front shape. Under loading conditions of the dysplastic hip, the octahedral shear stress was much larger on the medial side than on the lateral side, which promoted growth on the medial side and resulted in coxa valga. These results indicate that abnormal forces on the prenatal hip might influence total bone morphology and the development of DDH. These findings might help in understanding the etiology and pathology of other developmental bone deformities.  相似文献
2.
Garimella R  Bi X  Camacho N  Sipe JB  Anderson HC 《BONE》2004,34(6):961-970
During endochondral ossification (EO), cartilage is replaced by bone. Chondrocytes of growth plate undergo proliferation, maturation, hypertrophy, matrix vesicle (MV) biogenesis and programmed cell death (PCD, apoptosis). The in vitro system presented here provides a potential experimental model for studying in vitro differentiation and MV biogenesis in chondrocyte cultures. Chondrocytes were obtained from collagenase-digested tibial and femoral growth plate cartilage of 7-week-old rachitic rats. The isolated chondrocytes were plated as monolayers at a density of 0.5 × 106 cells per 35-mm plate and grown for 17 days in BGJb medium supplemented with 10% fetal bovine serum, 50 μg/ml ascorbic acid. Light microscopy revealed Sirius red-positive, apparent bone matrix in layers at the surfaces of cartilaginous nodules that developed in the cultures. The central matrix was largely alcian blue staining thus resembling cartilage matrix. Electron microscopy revealed superficial areas of bone like matrix with large banded collagen fibrils, consistent with type I collagen. Most of the central matrix was cartilaginous, with small fibrils, randomly arranged consistent with type II collagen. The presence of peripheral type I and central type II and type X collagen was confirmed by immunohistochemical staining. Immunohistochemistry with anti-Bone morphogenetic proteins 2, 4 and 6 showed that BMP expression is associated with maturing hypertrophic central chondrocytes, many of which were TUNEL positive and undergoing cell death with plasma membrane breaks, hydropic swelling and cell fragmentation. During early mineralization, small radial clusters of hydroxyapatite-like mineral were associated with matrix vesicles. Collagenase digestion-released MVs from the cultures showed a high specific activity for alkaline phosphatase and demonstrated a pattern of AMP-stimulated nonradioactive 40Calcium deposition comparable to that observed with native MVs. These studies confirm that primary cultures of rat growth plate chondrocytes are a reasonable in vitro model of growth plate histotype, MV biogenesis and programmed cell death.  相似文献
3.
Osteoprotegerin (OPG) is a novel secreted member of the tumor necrosis factor receptor family which plays a crucial role in negative regulation of osteoclastic bone resorption. We investigated both the quantity and quality of heterotopic new bone induced by crude bone morphogenetic protein (BMP) as a means of examining bone metabolism by bisphosphonate administration in OPG−/− mice. Four weeks after implantation of crude BMP, the volume of heterotopic new bone in OPG−/− mice without alendronate was significantly less than in wild-type (WT) mice. Alendronate treatment of OPG−/− mice resulted in enhancement of the volume of heterotopic new bone. Histological findings revealed that WT mice showed normal bone formation with persistent cartilage that was interspersed with islands of bone. In contrast, the cartilage was replaced by trabecular bone and bone marrow adipocytes in OPG−/− mice without alendronate. However, some cartilage was still present in OPG−/− mice with alendronate compared to those without alendronate. All bone formation-related parameters and bone resorption-related parameters were significantly lower in OPG−/− mice with alendronate than in those without alendronate. These findings suggest that in stimulated osteoclastogenesis without OPG, osteoinductive activity induced by crude BMP is inhibited and endochondral ossification induced by crude BMP is accelerated. On the other hand, alendronate treatment of OPG−/− mice caused osteoinductive activity induced by crude BMP to increase and endochondral ossification induced by crude BMP to be decelerated. In conclusion, inhibition of stimulated osteoclastogenesis results in the enhancement of new bone formation and normalization of endochondral ossification.  相似文献
4.
5.
The growth/differentiation factors (GDFs) are a subgroup of the bone morphogenetic proteins best known for their role in joint formation and chondrogenesis. Mice deficient in one of these signaling proteins, GDF-5, exhibit numerous skeletal abnormalities, including shortened limb bones. The primary aim of this study was determine whether GDF-5 deficiency would alter the growth rate in growth plates from the long bones in mice and, if so, how this is achieved. Stereologic and cell kinetic parameters in proximal tibial growth plates from 5-week-old female GDF-5 -/- mice and control littermates were examined. GDF-5 deficiency resulted in a statistically significant reduction in growth rate (-14%, p=0.03). The effect of genotype on growth rate was associated with an altered hypertrophic phase duration, with hypertrophic cells from GDF-5 deficient mice exhibiting a significantly longer phase duration compared to control littermates (+25%, p=0.006). These data suggest that one way in which GDF-5 might modulate the rate of endochondral bone growth could be by affecting the duration of the hypertrophic phase in growth plate chondrocytes.  相似文献
6.
Young rats fed a low calcium and vitamin D deficient diet for 2 weeks developed hypocalcemia and increased alkaline phosphatase activity in serum. The serum alkaline phosphatase activity (pNPPase) was found to be of skeletal origin. In accordance, the total non-specific alkaline phosphatase (pNNPase) activity in the microsomal fraction of tibial epiphyseal cartilage and metaphysis increased in the deficiently fed group when compared to the normal group. An increased activity in the microsomal fraction of tibial epiphyseal cartilage and metaphysis was shown both for inorganic pyrophosphatase and total ATP-degrading enzyme activity in the deficient group. This was also found in the presence of R 8231, indicating an increased activity of Ca2+-ATPase, shown to be present in both the epiphyseal plate and the metaphysis. These increased enzyme activities were consistent with the known effects of hypocalcemia and/or parathyroid hormone (PTH) on bone alkaline phosphatase activity. The increase in Ca2+-ATPase might, however, be a direct response to the hypocalcemia present in the deficient animals. Furthermore, the findings in the present study support the view that the same alkaline phosphatase iso-enzyme is present at different calcification loci.  相似文献
7.
Summary The changes in lipids occurring during the process of endochondral ossification have been characterized by studying the discrete phases of matrix-induced endochondral bone formation in the rat. Calcium-acidic phospholipid-phosphate complexes were shown to increase in concentration during cartilage calcification (day 9) and to peak in content during early bone formation (day 11–13), the times during which the rate of mineral deposition, as indicated by the change in ash weight was greatest. These data support the hypothesis that the calcium-acidic phospholipid-phosphate complexes play a role in thein vivo initiation of hydroxyapatite deposition. The overall lipid composition of the induced matrix newly formed cartilage (days 7–9) was comparable to that of normal cartilage, with the phospholipid composition matching that of chondrocyte plasma membranes. Times of vascular invasion and formation of marrow cavities were marked by elevated total lipid and triglyceride contents.  相似文献
8.
Summary Proteoglycans from bovine nasal septa and from the Swarm rat chondrosarcoma were isolated as aggregates (PGC) and as monomers (PGS). Portions of the PGC preparations were degraded with cathepsin D or chondroitinase AC. Chondroitin sulfates were isolated by differential precipitation from alkaline digests of the PGS from bovine nasal septa. The effects of these preparations at concentrations up to 2 mg/ml on the precipitation of tricalcium phosphatein vitro at pH 7.8 in 16 hours at 25°C were ascertained. To this end, the amounts of calcium and phosphate in the precipitates and in the supernates were determined. The PGC preparations were found to be very effective inhibitors; in the presence of 2 mg/ml, precipitate did not form. The PGS preparations were less effective than the PGC preparations; in the presence of 2 mg/ml, about 20% as much calcium phosphate precipitated as in their absence. The chondroitinase AC-degraded preparations at concentrations equivalent to 2 mg/ml of the PGC preparations were approximately as effective as the PGS preparations. On the other hand, the cathepsin D-degraded PGC preparations and the chondroitin sulfate chains were relatively poor inhibitors. Although the viscosity of the solutions may have influenced the rate at which the precipitates settled to the bottom of the bubes, the amounts of the tricalcium phosphate formed were related to the composition and concentration of the proteoglycan preparations.  相似文献
9.
Summary Proteoglycans from bovine nasal septa or the Swarm rat chondrosarcoma, as potassium salts, effectively inhibit the precipitation of tricalcium phosphatein vitro at pH 7.8. The same preparations, and many other similar preparations, however, do not site bind calcium, as assessed with a calcium ion specific electrode. However, after treatment of aggregate preparations of proteoglycans with EDTA, the preparations can site bind calcium. The amount thus bound is approximately equal to one-half the sum of the equivalents of the ester sulfate and the uronic acid carboxyl groups in the preparations. This latter observation suggested the possibility that the supposed potassium salts of the proteoglycans had, in the course of preparation, acquired calcium and held onto it strongly. In checking this possibility, using neutron activation analysis, it was found that some of the preparations do contain small amounts of calcium but these amounts are insufficient to saturate the binding sites potentially available to this end. In view of the above observations, it is suggested that the proteoglycans inhibit the formation of calcium phosphate precipitatesin vitro not because the calcium is site bound but because the calcium ions are territorially bound.  相似文献
10.
Summary A Fourier transform infrared spectrometer has been coupled with an optical microscope to study the distribution and characteristics of the mineral phase in calcifying tissues at 20μ spatial resolution. This represents the first biophysical application of this technique. High quality spectra were obtained in a relatively short scan time (1–2 minutes) from thin longitudinal sections of normal and rachitic rat femurs. Substantial spatial variations in the extent and structure of the mineral phase were observed as a function of spatial position both within and beyond the growth plates, as judged by the phosphate vibrations in the 900–1200 cm−1 spectral region. The current experiments reveal the utility of FT-IR micrscopy in identification of sites where mineralization has occurred. In addition to vibrations from the inorganic components, the Amide I and Amide II motions of the protein constituents are readily observed and may be useful as a probe of protein/mineral interactions.  相似文献
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