摘要:

AbstractThe ability of chondrocytes from calf articular cartilage to synthesize and assemble a mechanically functional cartilage‐like extracellular matrix was quantified in high cell density (∼ 107cell/ml) agarose gel culture. The time evolution of chondrocyte proliferation, proteoglycan synthesis and loss to the media, and total deposition of glycosaminoglycan (GAG)‐containing matrix within agarose gels was characterized during 10 weeks in culture. To assess whether the matrix deposited within the agarose gel was mechanically and electromechanically functional, we measured in parallel cultures the time evolution of dynamic mechanical stiffness and oscillatory streaming potential in uniaxial confined compression, and determined the intrinsic equilibrium modulus, hydraulic permeability, and electrokinetic coupling coefficient of the developing cultures. Biosynthetic rates were initially high, but by 1 month had fallen to a level similar to that found in the parent calf articular cartilage from which the cells were extracted. The majority of the newly synthesized proteoglycans remained in the gel. Histological sections showed matrix rich in proteoglycans and collagen fibrils developing around individual cells. The equilibrium modulus, dynamic stiffness, and oscillatory streaming potential rose to many times (>5X) their initial values at the start of the culture; the hydraulic permeability decreased to a fraction (∼1/10) that of the cell‐laden porous agarose at the beginning of the culture. By day 35 of culture, DNA concentration (cell density), GAG concentration, stiffness, and streaming potential were all ∼25% that of calf articular cartilage. The frequency dependence of the dynamic stiffness and potential was similar to that of calf articular cartilage. Together, these results suggested the formation of mechanically functi

ISSN:0736-0266    

DOI:10.1002/jor.1100100602

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

年代:1992

数据来源: WILEY

摘要:

AbstractIntact canine metacarpophalangeal and metatarsophalangeal joints were subjected to a variety of loads in vitro. Intraarticular fracture occurred in 19 joints loaded to an average force of 2.4 ± 0.4 kN with a corresponding loading rate of 88 ± 23 kN/s. The remaining 29 joints were without gross evidence of fracture with an average load and loading rate of 1.7 ± 0.9 kN and 64 ± 32 kN/s, respectively. In the fractured specimens, damage to the zone of calcified cartilage and subchondral bone was much more extensive than was initially evident by gross inspection when assessed by scanning electron microscopy. Cracks with associated step‐off displacement at the zone of calcified cartilage were found distant to the gross fractures. These findings were confirmed histologically. In addition, cracks localized to the zone of calcified cartilage were commonly identified histologically in specimens loaded in the range of 1.9–2.8 kN, but were not grossly fractured. The contact area determined with pressure‐sensitive film increased with increasing load up to the point of fracture. The average pressure generated at the articular cartilage surface at the time of fracture in this model is ≥40 MPa, and the fracture occurred at the contact site. Our findings suggest that failure in acute transarticular loading begins in the zone of calcified cartilage and subsequently involves the subchondral bone and overlying cartilage. This type of injury may contribute to the development of osteoarthritis after intraarticular fracture, or at high loads that do not result in gro

ISSN:0736-0266    

DOI:10.1002/jor.1100100603

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe interactions of bone cells with their extracellular matrix is of major importance in bone development, repair, and disease. We examined the ability of rat calvarial bone cells to adhere to various matrix proteins and to define the role of integrin cell‐substrate adhesion receptors in these interactions. Isolated newborn rat calvarial bone cells prelabeled with3H‐thymidine and plated on plastic wells that had been precoated with serial dilutions of various substrates showed typical dose‐response adherence curves to fibronectin, fibrinogen, laminin, vitronectin, and collagen I and IV. Cell adherence to poly‐D‐lysine, a nonspecific cell adherent, was high at all substrate concentrations>0.0001 μg/ml. A polyclonal anti‐rat integrin antibody blocked cell adhesion to all substrates tested except poly‐D‐lysine. Isolated rat calvarial bone cells were surface labeled with125I, extracted, and immunoprecipitated with polyclonal antibodies made against the rat integrin complex and peptides derived from the cytoplasmic domains of the α2, α3, and α5subunits. Analysis by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (nonreduced) identified four bands representing a mixture of integrins including the α1β1laminin/collagen receptor, the α5β1fibronectin receptor, and the αvβ3(or possibly αvβ5) vitronectin receptor. These experiments show that bone cells adhere to a wide variety of extracellular matrix proteins via specific integrins. Increased knowledge about the regulation of these receptors and the mechanisms by which they transmit information to the cell will be important for a more complete understanding of bone p

ISSN:0736-0266    

DOI:10.1002/jor.1100100604

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

年代:1992

数据来源: WILEY

摘要:

AbstractMagnesium is known to have an essential role in determining the properties of bone, but the way in which Mg exerts its actions remains unclear. Although long‐term Mg deficiency is known to produce osteopenia, the effects of short‐term Mg deficiency have not been established. To test the hypothesis that Mg deficiency results in an altered pattern of initial mineralization and concomitant altered bone properties, the radiographic, histologic, chemical, and mechanical properties of the bones of rats given a Mg‐deficient diet were compared to those of rats pair‐fed the same diet supplemented with Mg. Short‐term Mg‐deficiency in the diet of growing rats produced a significant decrease in both the trabecular bone volume and the mineral content of the newly formed metaphysis, a significant increase in the Ca:P ratio, and a slight, but significant increase in hydroxyapatite crystallite size and/or perfection in the metaphysis. Comparable, but not significant, trends were found in the diaphyses. Metaphyseal bone osteocalcin levels were reduced in the Mg‐deficient rats and lipid was more easily extracted from their bones. No detectable alterations in radiographic microstructure were noted. Mechanically, a significant decrease in the maximum three‐point bend strength of the femurs of Mg‐deficient rats was observed. These data support the hypothesis that short‐term Mg deficiency affects the pattern of bon

ISSN:0736-0266    

DOI:10.1002/jor.1100100605

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe effect of cast immobilization on blood flow to the tibial diaphysis was studied by the microsphere method, both before and after casting of one hindlimb of adult New Zealand White rabbits. Preliminary studies were undertaken to investigate the possibility of the reduction of tibial flow by the microspheres used for the control measurements of blood flow. There were no significant differences in the flows to the tibial diaphysis or skeletal muscle between the immobilized and control limbs after either 1 or 2 weeks. This similarity between control and experimental limbs indicates that immobilization had no major effect on tibial blood flow over and above the systemic effects of the procedure.

ISSN:0736-0266    

DOI:10.1002/jor.1100100606

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

年代:1992

数据来源: WILEY

摘要:

AbstractWe evaluated the in vivo animal tolerance to intraosseous infusion via the Osteoport pediatric implant (model 2005PSO, Lifequest Medical, San Antonio, TX, U.S.A.) into the proximal tibia of immature goats and investigated the osseous effects of intermittent and sustained increases in intraosseous pressure (IOP). In group 1 (n = 3) autogenous whole blood was continuously infused (CI) for 5 days at flow rates producing an IOP of 30–45 mm Hg. Group 2 animals (n = 3) underwent a 5‐s high‐pressure infusion (HPI) of lactated Ringer solution (LRS) producing an IOP of 90–125 mm Hg twice daily for 10 days. In group 3, the Osteoports were left in place 5 (n = 2) or 10 days (n = 2) and evaluated for patency at 72‐h intervals. An IOP>35 mm Hg produced clinical evidence of bone pain. Bone mineral density was significantly increased (p<0.05) in all implanted tibias (mean 1.04 g/cm2; range 0.87–1.21 g/cm2) compared with controls (mean 0.67 g/cm2; range 0.65–0.71 g/cm2). A nonsignificant increase (+9% to +31%) in periosteal new bone formation occurred in all implanted tibias. In the continuously infused group, there was a significant increase (p<0.05) in cancellous new bone formation (+ 483%), percentage eroded bone surface (+ 143%), and osteoclast covered bone surface (+ 255%) compared with controls. HPI of LRS did not produce significant bone changes. Seemingly, the Osteoport provided a ready means of intraosseous infusion and may be associated with less complications than current methods of continual vascular access. Bone changes correlated more with the duration than the magnitude of increased intraosse

ISSN:0736-0266    

DOI:10.1002/jor.1100100607

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

年代:1992

数据来源: WILEY

摘要:

AbstractBlood flow rates of the canine femoral head were experimentally determined during traction, compression, and hip joint tamponade using the hydrogen washout technique. In puppies, blood flow rate of the femoral head was significantly decreased with either traction or compression applied at one half body weight. Either maneuver, when combined with hip joint tamponade, reduced blood flow rate of the femoral head an average of more than 70% as compared with the initial control rate. In adult dogs, combinations of either traction or compression, at one‐half body weight, with hip joint tamponade did not significantly decrease blood flow rate of the femoral head as compared with control values. Perfusion defect of blue silicone could be observed only in puppies around the hip during combinations of traction or compression with hip joint tamponade and involved the posterior superior capital branches of the medial circumflex artery and the arteries in the ligamentum teres. These experimental data may have important implications for the pathogenesis of iatrogenic avascular necrosis in the treatment of congenitally dislocated hip, Legg‐Perthes disease, and avascular necrosis following nondisplaced femoral neck fract

ISSN:0736-0266    

DOI:10.1002/jor.1100100608

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

年代:1992

数据来源: WILEY

摘要:

AbstractPathological changes in bone have been related to a preceding impediment of the arterial or venous bone circulation and hypoxia. In this study, we analyzed the feasibility of mass spectrometry in measuring intraosseous oxygen and carbon dioxide. The partial pressures were also measured in intraosseous blood samples, and blood flow in bone was measured with the radioactive microspheres technique. The average partial pressure of oxygen in the lateral femoral condyle was 34 ± 1.6 mm Hg when measured in intraosseous blood samples and 36.3 ± 2.3 mm Hg when measured with the on‐line mass spectrometer, with significant correlation between the methods. The absolute value of the partial pressure of carbon dioxide measured in situ with mass spectrometry was correlated with the value in the withdrawn blood. There was no significant difference in partial pressures of oxygen and carbon dioxide between the two sides or between repetitive measurements. Arterial occlusion resulted in severe hypoxia, whereas more moderate changes followed venous occlus

ISSN:0736-0266    

DOI:10.1002/jor.1100100609

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

年代:1992

数据来源: WILEY

摘要:

AbstractAn ex vivo canine tibia preparation was perfused at a constant rate with aerated (95% O2‐5% CO2) Krebs‐Ringer solution for 24 h. Bolus injections of norepinephrine (0.125‐0.5 μg) were given and then acetylcholine (5 × 10−5M) was used to stimulate endothelial production of smooth muscle relaxing factors. Following 1 h of perfusion the addition of acetylcholine resulted in significant attenuation of the response to norepinephrine (p<0.001). After 4 h perfusion acetylcholine did not attenuate the norepinephrine response, but addition of I‐arginine (the precursor of endothelial‐derived relaxing factor) resulted in significant attenuation in the presence of acetylcholine (p<0.005). At 6, 12, and 24 h the acetylcholine did not attenuate the norepinephrine response. It is concluded that normothermic, continuous perfusion with oxygenated Krebs‐Ringer solution results in normal endothelial eccrine activity up to 1 h. Following this period there is substrate depletion but endothelial eccrine function can be demonstrated for up to 4 h. At 6 h this function cannot be demonstrated, suggesting degradation of the functional integrity of

ISSN:0736-0266    

DOI:10.1002/jor.1100100610

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

年代:1992

数据来源: WILEY

摘要:

AbstractAn analysis is presented of the balance between the accumulation and repair of fatigue damage in osteonal bone. Fatigue damage is defined in terms of cracks seen histologically when precautions are taken to avoid preparation artifact. The rate of occurrence of such damage is assumed to be proportional to the product of applied peak‐to‐peak stress, raised to a power, and the loading frequency. The rate of damage repair is assumed to be proportional to the activation rate for osteonal remodeling, and to the mean cross‐sectional area of the resulting osteons. An additional factor is introduced to account for the possibility that damage provokes nearby remodeling. The theory is used to compare data from previous experiments of two types: fatigue‐to‐failure, and studies in which histologically observable cracks are made more numerous by repetitive loading. The analysis shows that there is a measure of agreement between the results of the two kinds of experiments, but the current data are too limited, and the results are too dependent on the mode of loading, to adequately test the theory. However, the analysis provides a framework for designing experiments to more efficiently clarify the relationships between fatigue failure, cracks seen in histologic sections, and the rate at which such cracks are repaired by osteonal r

ISSN:0736-0266    

DOI:10.1002/jor.1100100611

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

年代:1992

数据来源: WILEY