摘要:

AbstractThe biomechanical consequences of an isolated overload to the vertebral body may play a role in the etiology of vertebral fracture. In this context, we quantified residual strains and reductions in stiffness and ultimate load when vertebral bodies were loaded to various levels beyond the elastic regimen and related these properties to the externally applied strain and bone density. Twenty‐three vertebral bodies (T11‐L4, from 23 cadavers aged 20–90 years) were loaded once in compression to a randomized nominal strain level between 0.37 and 4.5%, unloaded, and then reloaded to 10% strain. Residual strains of up to 1.36% developed on unloading and depended on the applied strain (r2= 0.85) but not on density (p = 0.25). Percentage reductions in stiffness and ultimate load of up to 83.7 and 52.5%, respectively, depended on both applied strain (r2= 0.90 and r2= 0.32, respectively) and density (r2= 0.23 and r2= 0.22, respectively). Development of residual strains is indicative of permanent deformations, whereas percentage reductions in stiffness are direct measures of effective mechanical damage. These results therefore demonstrate that substantial mechanical damage—which is not visible from radiographs—can develop in the vertebral body after isolated overloads, as well as subtle but significant permanent deformations. This behavior is similar to that observed previously for cylindrical cores of trabecular bone. Taken together, these findings indicate that the damage behavior of the lumbar and lower thoracic vertebral body is dominated by the trabecular bone and may be an important factor in the etiology of vertebral

ISSN:0736-0266    

DOI:10.1002/jor.1100180502

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2000

数据来源: WILEY

摘要:

AbstractDevelopment of noninvasive mechanical tests to monitor fracture healing has been hindered because relationships between bone geometry, measurement conditions, and fracture callus strength are not well understood. Beam theory was used to analyze the effects of fracture length, fracture location, end conditions, and fracture callus stiffness on mechanical properties (resonant frequency, bending stiffness, and torsional stiffness) of healing bone. Actual bone mineral geometry from a human tibia, quantified every 1 mm, was used in the beam analysis. Geometry of the fracture callus segment was uniformly scaled from the values for intact bone. Experimental tests on multisegmented machined rods were used to verify analytical methods. Mechanical properties of the healing bone initially increased very rapidly to 30–70% of the stiffness of intact bone, depending on the configuration. The increases then tapered off dramatically. Lateral bending stiffness was sensitive to changes in callus properties for a larger portion of the healing process than was either torsional stiffness or resonant frequency. Because callus strength increases at half the rate of callus stiffness, measures of whole‐bone mechanical properties can provide insight into changes in callus strength until a maximum of less than one‐half the strength of intact bone is regained. The analytical method presented is proposed for clinical use to develop individualized models of bone, fracture, and fixation conditions to identify early stages of healing. Because increases in whole‐bone mechanical properties are small in the later stages of fracture healing, however, such measures must be used prudently beyond the initial

ISSN:0736-0266    

DOI:10.1002/jor.1100180503

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2000

数据来源: WILEY

摘要:

AbstractThis scanning electron microscopic study examined the spatial and temporal features of proliferating vessels of regenerating bone tissue and blood supply during distraction osteogenesis. A rat model of tibial lengthening was used with a protocol divided into a latency period of 7 days, a distraction period that lasted 14 days with a daily distraction rate of 0.5 mm on two steps, and a consolidation period of 21 days. Vascular casting was done on the hindlimbs before osteotomy and on postoperative days 7, 14, 21, 28, and 42. Scanning electron microscopic findings were correlated with radiological and histological observations. On days 7 and 14, the proliferation of periosteal vessels was pronounced and there was distinct subperiosteal bone formation on the osteotomized surfaces. On day 2, vascular branches from the medullary canal of the host bone formed a vascular network, which gave rise to multiple axial, straight vascular branches, running parallel to the direction of distraction, toward the interzone, in accordance with the progress of mineralization. On day 28, the periosteum provided vascularization to the peripheral side of the interzone whereas the center of the interzone was still relatively avascular. On day 42, the periosteal and medullary vascular channels were completely connected at the distraction site including the interzone, which was occupied by developing and mature bone trabeculae. These results suggest that vascular proliferation occurs actively during the latency and distraction periods and then gradually decreases over time. A close temporal and spatial relationship exists between formation of regenerated bone and vascular proliferation of the periosteum and medullary canal.

ISSN:0736-0266    

DOI:10.1002/jor.1100180504

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2000

数据来源: WILEY

摘要:

AbstractSesamoid bones form by the endochondral ossification of sesamoid cartilages. This ossification process is thought to be similar to that responsible for the formation of secondary ossific nuclei in long‐bone epiphyses. Sesamoids ossify much later in development than do epiphyses, however, and bone formation within sesamoids often begins by way of multiple ossific nuclei. Endochondral growth and ossification in the formation of secondary ossific nuclei have previously been correlated with distributions of the octahedral shear and hydrostatic stresses generatedin vivowithin cartilage anlagen. In this study, we used two‐dimensional finite element analysis to predict the distributions of octahedral shear and hydrostatic stresses in an idealized model of a sesamoid cartilage subjected toin vivoloading. We examined the influence of sesamoid joint conformity. The distribution of an osteogenic stimulus was calculated with an approach similar to that used to predict epiphyseal ossification. The results suggest that, compared with conforming joints, nonconformity between the sesamoid cartilage and its articulating surface, which arises during early development, produces higher contact pressures within the sesamoid and leads to a thicker articular cartilage layer. For a nonconforming joint surface, the results suggest that ossification is favored anywhere within a broad internal region of the sesamoid, whereas a layer at the articular surface will remain cartilaginous. These findings highlight the subtle differences between ossification processes in epiphyses and sesamoids, indicating that the mechanical stress environment in sesamoids produces a diffuse stimulus leading to the onset of ossification and that the degree of joint nonconformity may influence the thickness of the articular cartilage la

ISSN:0736-0266    

DOI:10.1002/jor.1100180505

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2000

数据来源: WILEY

摘要:

AbstractCartilage oligomeric matrix protein has been implicated as an important component of endochondral ossification because of its direct effects on chondrocytes. The importance of this protein for skeletal development and growth has been recently illustrated by the identification of mutations in cartilage oligomeric protein genes in two types of inherited chondrodysplasias and osteoarthritic phenotypes: multiple epiphyseal dysplasia and pseudoachondroplasia. In the present study, we report the presence of cartilage oligomeric protein in embryonic and adult osteoblasts. A foot from a 21‐week‐old human fetus, subchondral bone obtained from knee replacement surgery in an adult patient, and a limb from a 19‐day‐postcoital mouse embryo were analyzed with immunostaining andin situhybridization. In the human fetal foot, cartilage oligomeric protein was localized to osteoblasts of the bone collar and at the newly formed bone at the growth plate and bone diaphyses. Immunostaining was performed on the adult subchondral bone and showed positive intra‐cellular staining for cartilage oligomeric protein of the osteoblasts lining the trabecular bone. There was no staining of the osteocytes. Immunostaining of the mouse limb showed the most intense staining for cartilage oligomeric protein in the hypertrophic chondrocytes and in the surrounding osteoblast cells of the developing bone. Cartilage oligomeric protein mRNA and protein were detected in an osteoblast cell line (MG‐63), and cartilage oligomeric protein mRNA was detected from human cancellous bone RNA. These results suggest that the altered structure of cartilage oligomeric protein by the mutations seen in pseudoachondroplasia and multiple epiphyseal dysplasia may have direct effects on osteoblasts, contributing to the pathogenesis of these geneti

ISSN:0736-0266    

DOI:10.1002/jor.1100180506

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2000

数据来源: WILEY

摘要:

AbstractWe studied the inhibitory effects of the fluoroquinolones levofloxacin, ciprofloxacin, and trova‐floxacin on growth and extracellular matrix mineralization in MC3T3‐E1 osteoblast‐like cell cultures. Levo‐floxacin had the least inhibitory effect on cell growth, with a 50% inhibitory concentration of approximately 80 μg/ml at 48 and 72 hours. Ciprofloxacin had an intermediate degree of inhibition, with a 50% inhibitory concentration of 40 μg/ml at 48 and 72 hours. Trovafloxacin exerted a profound inhibitory effect on cell growth, with a 50% inhibitory concentration of 0.5 μg/ml, lower than clinically achievable serum levels. The decreased cell counts with up to 2.5 μg/ml of trovafloxacin and with up to 40 μg/ml of ciprofloxacin were not associated with decreased rates of 5‐bromo‐2′‐deoxyuridine incorporation per cell. Alatrovafloxacin, the L‐alanyl‐l‐alanine prodrug of trovafloxacin, exerted effects on proliferation and 5‐bromo‐2′‐deoxyuridine incorporation similar to those of the parent compound. The quinolones evaluated also inhibited extracellular matrix mineralization by MC3T3‐E1 cells. Treatment of confluent cultures with trovafloxacin, ciprofloxacin, or levofloxacin resulted in strong inhibition of calcium deposition, as determined on day 14 by alizarin red staining and biochemical analysis. The effect was apparent with 2.5‐5 μg/ml of each of the three antibiotics tested and progressively increased to more than a 90% decline in the calcium/protein ratio with 20‐40 μg/ml antibiotic concentration. Furtherin vivostudies are advocated to evaluate the relevance of thein vitrocytotoxicity reported he

ISSN:0736-0266    

DOI:10.1002/jor.1100180507

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2000

数据来源: WILEY

摘要:

AbstractOsteonecrosis of the femoral head often results in secondary osteoarthritis of the hip joint; however, the pathologic processes underlying the destruction of articular cartilage are not fully understood. Molecular markers in the hip joint fluids were measured to examine the changes in turnover of cartilage and other joint tissues. Marker data were related to clinical, radiological, and histopathological changes in the articular cartilage of the hip. Forty‐five patients (median age: 43 years) were studied. The median time between the onset of symptoms and sampling of hip synovial fluid was 6 months. Aggrecan fragments, C‐propeptide of type‐II collagen, matrix metalloproteinase‐3, and tissue inhibitor of metalloproteinases‐1 levels in joint fluid were determined by immunoassay. Osteonecrosis of the femoral head was graded by radiology as minimal collapse of the femoral head (stage 2: 26 patients), severe collapse (stage 3: 15 patients), or severe collapse with osteoarthritis (stage 4: four patients). Histologica changes of the articular cartilage, consistent with early‐stage osteoarthritis, were evident at stage 3 and were more advanced at stage 4. The average concentrations of proteoglycan fragments and C‐propeptide of type‐II collagen were 207 (SD 182) μg/ml and 19.6 (SD 19.3) ng/ml, respectively. The average concentrations of matrix metalloproteinase‐3 and tissue inhibitor of metalloproteinases‐ 1 were 177 (SD 291) nM and 23.0 (SD 9.9) nM, respectively. Measurable levels for all markers assayed were noted in the earliest stage of the disease, only a few months after the onset of symptoms and well before the appearance of radiological changes. Levels of matrix metalloproteinase‐3 and molar ratios of matrix metalloproteinase‐3/tissue inhibitor of metalloproteinases‐1 were higher in early stage disease t

ISSN:0736-0266    

DOI:10.1002/jor.1100180508

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2000

数据来源: WILEY

摘要:

AbstractAn increased risk of fracture is a feature of rheumatoid arthritis and of animal models of inflammatory arthritis. We examined geometrical changes in the metaphyseal cortex of the distal femur in an animal model of inflammatory arthritis. Additionally, we examined the effect of a bisphosphonate in preventing these changes. Five groups of rabbits were studies: normal controls, those with inflammatory arthritis, and three groups with arthritis treated with bisphosphonate. To determine geometrical properties, image analysis was performed on digitized cross sections of the femoral metaphyseal cortices. The results demonstrated that the posterior cortical wall was significantly less thick in rabbits with arthrits than in normal rabbits and in the rabbits in the three bisphosphonate treatment groups (p<0.05). Moment of inertia about the lateral‐medial axis was reduced inrabbits with arthritis compared with normal rabbits (p<0.05). Cross‐sectional area was not significantly different between groups. The changes suggest a mechanism of weakening of bone in arthritis; when the results are coupled with results of previous porosity studies, severe directional weakness is apparent. Bisphosphonate was effective in preserving bone integrity in inflammatory arthri

ISSN:0736-0266    

DOI:10.1002/jor.1100180509

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2000

数据来源: WILEY

摘要:

AbstractCartilage was obtained from eight matched knee (tibiofemoral and femoropatellar) and ankle (talocrural) joints of five different donors (both left and right from donors 14, 22, and 38 years of age, and left only from donors 31 and 45 years of age) within 24 hours of death. All cartilage was graded as normal by the macroscopic visual Collins' scale and the histological Mankin scale. Cylindrical disks of cartilage were harvested from 10 sites within the tibiofemoral and femoropatellar joint surfaces and four sites within the talocrural joint, and uniaxial confined compression measurements were performed to quantify a spectrum of physical properties including the equilibrium modulus, hydraulic permeability, dynamic stiffness, streaming potential, electrokinetic coupling coefficient, and electrical conductivity. Matched specimens from the same 14 sites were used for complementary measurements of biochemical composition and molecular interaction, including water content, hypotonic swelling behavior, and sulfated glycosaminoglycan and collagen contents. In comparison of the top 1‐mm slices of talar cartilage with the top 1‐mm of tibiofemoral cartilage, the talar cartilage appeared denser with a higher sulfated glycosaminoglycan content, lower water content, higher equilibrium modulus and dynamic stiffness, and lower hydraulic permeability. The equilibrium modulus increased with increasing sulfated glycosaminoglycans per wet weight and decreased with increasing water content for all joint surfaces. Multiple linear regression showed that greater than 80% of the variation in the equilibrium modulus could be accounted for by variations in the biochemical parameters (water content, sulfated glycosaminoglycans/wet weight, and hydroxyproline content/wet weight) for each joint surface. Nonhomogeneous depth‐dependent changes in the physical properties and biochemical composition of full‐thickness distal femoral cartilage were consistent with previous reports. Since the compressive deformation of cartilage during cyclic loading is confined to the more superficial regions, the differences in properties of the upper regions of the talar compared with tibiofemoral or femoropatellar cartilage may be important in the etiology of osteoar

ISSN:0736-0266    

DOI:10.1002/jor.1100180510

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2000

数据来源: WILEY

摘要:

AbstractRelatively little is known about the contractile behavior of the human articular chondrocyte. Other connective tissue cells are known to express a contractile actin isoform, α‐smooth muscle actin, in response to injury, at selected stages of wound healing, and in certain pathological conditions. This and recent work demonstrating contractile behavior in adult canine articular chondrocytesin vitroprompted the present study of the distribution of α‐smooth muscle actin‐containing chondrocytes in human articular cartilage. Approximately 75% of the chondrocytes in the superficial region of cartilage expressed α‐smooth muscle actin as demonstrated by immunohistochemistry. In contrast, only approximately 10% of the cells in the deep region stained for this contractile actin isoform. There was no correlation of the percentage of α‐smooth muscle actin‐positive cells in either region with Mankin grade or with age. This is the first report of a contractile potential for human articular chondrocytes. The roles of α‐smooth muscle actin in these cells warrant further investigation. The question of whether it is necessary to refer to these cells as myochondroc

ISSN:0736-0266    

DOI:10.1002/jor.1100180511

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2000

数据来源: WILEY