ISSN:0884-0431    

DOI:10.1002/jbmr.5650071402

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1992

数据来源: WILEY

摘要:

AbstractThe continuing ability of the skeleton to withstand functional loads without damage requires that bone mass and architecture are adjusted according to the loads experienced. Load bearing is the only functional influence that requires a particular bone architecture, and functionally engendered strains within the bone tissue provide the only feedback containing the necessary information on the relationship between current architecture and prevailing load history. The specific strain‐related objectives of the adaptive modeling and remodeling response to load bearing have not been adequately defined. They appear to be different for cortical and cancellous bone and vary according to cortical location. Experiments suggest that adaptive modeling and remodeling is sensitive to dynamic but not static strain change and that the osteogenic response to a period of dynamic strain is quickly saturated but is higher when the rate of change in strain is high and the distribution of strain unusual. Presumably it is the cumulative effect of this osteogenic response to load bearing that normally maintains bone mass above that seen in disuse situations. Through their independent effects on bone cell behavior, nutritional and hormonal factors can enable, enhance, limit, or frustrate full expression of the osteogenic response to strain change. However, such systemic factors do not appear to be able to engender or successfully imitate the sustained cumulative local response to load bearing that normally maintains functionally appropriate bone mass and architecture. Experiments in vivo and in vitro suggest that in osteocytes and surface osteoblasts the almost immediate response to strain change is increased production of prostacyclin. Surface osteoblasts also produce prostaglandin E. Only 5 minutes after loading, glucoses‐phosphate dehydrogenase activity in osteocytes is increased in a local strain magnitude‐related manner, and 24 h later there is an increase in osteocyte RNA. Exogenous PGE2and PGI2imitate the G6PD response in both osteocytes and osteoblasts, but only PGI2imitates the loading‐related increase in RNA in these two cell types. Indomethacin reduces the osteogenic response to loading in vivo and both the G6PD and RNA responses to loading in vitro. We hypothesize that the strain‐related increase in PGE influences the synthetic activity of surface bone cells directly, whereas the strain‐related increase in PGI2additionally influences modeling and remodeling through the production of a cytokine or growth factor for which the loading‐related RNA is coded. It may be at the stage of cytokine interaction that the potentially competing or complementary effects on modeling and remodeling of the loading and hormonal environment

ISSN:0884-0431    

DOI:10.1002/jbmr.5650071403

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1992

数据来源: WILEY

摘要:

AbstractEmbryonic chick bone cells express various types of ionic channels in their plasma membranes for as yet unresolved functions. Chick osteoclasts (OCL) have the richest spectrum of channel types. Specific for OCL is a K+channel, which activates (opens) when the inside negative membrane potential (Vm) becomes more negative (hyperpolarization). This is consistent with findings of others on rat OCL. The membrane conductance constituted by these channels is called the inward rectifying K+conductance (GKi), or inward rectifier, because the hyperpolarization‐activated channels cause cell‐inward K+current to pass more easily through the membrane than outward K+current. BesidesGKi, channels, OCL may express two other types of voltage‐activated K+channels. One constitutes the transient outward rectifying K+conductance (GKto), which is activated upon making the membrane potential less negative (depolarization) but has a transient nature. This conductance favors transient K+conduction in the cell‐outward direction. TheGKtoalso occurs in a small percentage of cells in osteoblast (OBL) and periosteal fibroblast (PFB) cultures. The other OCL K+conductance, theGKCa, is activated by both membrane depolarization and a rise in [Ca2+]i.GKCachannels are also present in the other chick bone cell types, that is, OBL, osteocytes (OCY), and PFB. Furthermore, in excised patches of all bone cell types, channels have been found that conduct anions, including CI−and phosphate ions. These channels are only active aroundVm= 0 mV. While searching for a membrane mechanism for adaptation of bone to mechanical loading, we found stretch‐activated channels in chick osteoclasts; other investigators have found stretch‐activated cation channels (K+or aselective) in rat and human osteogenic cell lines. In contrast to other studies on cell lines or OBL from other species, we have not found any of the classic macroscopic voltage‐activated calcium conductances (GCa) in any of the chick bone cells under our experimental conditions. However, our fluorescence measurements of [Ca2+]iin single cells indicate the presence of Ca2+conductive pathways through the plasma membrane of osteoblastic cells and osteoclasts, consistent with other studies. We discuss possible roles forGKi,GKCa, and anion channels in acid secretion by OCL and for stretch‐activated channels

ISSN:0884-0431    

DOI:10.1002/jbmr.5650071404

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1992

数据来源: WILEY

摘要:

AbstractThe role of in vivo mechanical loading histories in normal skeletogenesis is related to the process of adaptive, stress‐regulated bone remodeling in the adult. The results of many previous computer models for endochondral ossification and bone modeling and remodeling are reviewed. These studies support the view that simple stress‐related mathematical algorithms or “construction rules” can be used to emulate normal skeletal development and architectural construction. Such mathematical rules presumably represent the net result of biophysical phenomena influencing cell metabolism and biosynthetic activity. These rules are also successful in describing the adaptation of adult bone to changes in tissue stresses. The findings suggest that stress‐related functional adaptation in mature bones may be merely the adult manifestation of the same mechanical construction rules that guide and constrain normal de

ISSN:0884-0431    

DOI:10.1002/jbmr.5650071405

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1992

数据来源: WILEY

摘要:

AbstractThe use of hydrostatic pressure to apply mechanical stress to bone organ cultures is reviewed. Ossifying long bones and calvarial rudiments are sensitive to this type of stress. Intermittent hydrostatic compression of near physiologic magnitude (ICF) has anabolic effects on mineral metabolism in such rudiments, and continuous hydrostatic stress of high magnitude (CCP) has catabolic effects. The effects of ICF may be ascribed to shear stress generated at tissue interphases of different chemical and mechanical properties. Local factors, such as prostaglandins and growth factors, seem to be involved in the tissue response to mechanical stress.

ISSN:0884-0431    

DOI:10.1002/jbmr.5650071406

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1992

数据来源: WILEY

摘要:

AbstractPeriosteal cells grown in macroporous microcarrier bead columns were cyclically loaded with compressive force using a newly developed model. In response to 1/2 h of cyclic compression, RNA synthesis increased significantly by twofold, from 113.4, 19.6 to 260.7 + 363 (plt; 0.01) after 16 h, whereas DNA synthesis did not increase significantly after 24 h. The microcarrier bead model was calibrated using a linear volume displacement transducer with a range of strain magnitudes applied across the column of 1000–6000 μstra

ISSN:0884-0431    

DOI:10.1002/jbmr.5650071407

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1992

数据来源: WILEY

摘要:

AbstractThe structure of metatarsal bones from 18‐day‐old rats subjected to intermittent mechanical force in organ culture are reported. The application of mechanical force enhances the osteoid thickness and osteoblast number in the periosteum and increases the number of viable osteocytes. These results indicate that (1) the mature bone tissue survives in organ cultures; (2) the mechanical forces better preserve the structure of the osteocytes and stimulate the osteoblasts, and (3) stimulate the osteogene

ISSN:0884-0431    

DOI:10.1002/jbmr.5650071408

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1992

数据来源: WILEY

摘要:

AbstractSince the work of Pauwels and his successors, it has been possible to use the distribution of subchondral bone density within a joint surface as a metric parameter that can reflect the principal long‐term stress acting upon a joint. However, the x‐ray densitometry method he employed cannot be applied to living people. A procedure was therefore developed whereby CT osteoabsorptiometry (CT OAM), based on the use of computed tomography, allows the distribution pattern of the density to be demonstrated in living subjects. This method has now been further developed, so that the form of the individual joint surfaces can be included by means of a three‐dimensional reconstruction program. This method is presented here. In addition, selected representative examples of various joints from normal people, athletes, and patients are used to demonstrate the use of CT OAM. In these examples from living subjects, regularly occurring, reproducible distribution patterns of subchondral bone density can be recorded, reflecting changes in mechanical stresses on a joint (increased stress, reduced stress, and disorders of joint mechanics). CT osteoabsorptiometry is demonstrated as a suitable noninvasive technique for investigating the individual long‐term stresses (loading history) acting on a livin

ISSN:0884-0431    

DOI:10.1002/jbmr.5650071409

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1992

数据来源: WILEY

摘要:

AbstractAll tissues of the joint are affected in some way in osteoarthritis because the joint is an interactively functioning unit. Our goal was to investigate the combined responses of articular cartilage and subchondral bone to altered loading conditions to improve our understanding of the physiology of these two components and, ultimately, the pathophysiology of osteoarthritis. A group of 20 female beagle dogs were divided pairwise into runners (n= 10) and controls (n= 10). The running training on a treadmill started at the age of 15 weeks, and during the following 40 weeks the running distance was gradually increased to 40 km/day with a 15° uphill inclination. With this daily running distance the beagles ran another 15 weeks. The samples for histology were taken from 11 different locations of the knee joint. Subchondral bone and articular cartilage histomorphometry was carried out in three different regions of the specimens (central, middle, and peripheral regions) using an image‐analyzing system and an eyepiece graticule. In all regions of the articular cartilage, both the uncalcified and calcified cartilage showed slightly increased thickness in the runner dogs. The change was more evident in the peripheral and the central areas. The thickness of the subchondral bone plate tended to be higher in runners, too. Bone histomorphometric parameters showed significant signs of increased remodeling. The most notable change was the enlargement of the bone formation surface. The most intense remodeling was usually observed either centrally or peripherally in the articular surface. The strongest increase in trabecular bone volume and thickness of the cartilage was recorded in the femoropatellar area. These topographically confined and separate responses of the articular cartilage and subchondral bone to long‐distance running are presumably adaptive processes that provide better congruence and biomechanical stability to the articulating bone ends. Under pathologic conditions these processes may initiate the subchondral etiopathogenesis of osteoarthritis by impairing the shock‐absorbing capacity of the

ISSN:0884-0431    

DOI:10.1002/jbmr.5650071410

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1992

数据来源: WILEY

摘要:

AbstractThe rate of remodeling in the region of a bone defect exceeds normal tissue activity. It was Frost who described this reaction as the regional acceleratory phenomenon (RAP). We previously showed that restoration of a local bone defect in the rat leads not only to RAP but also leads to a systemic acceleration of osteogenesis (systemic acceleratory phenomenon, SAP) in distant sites of the skeleton. In this study we investigated the impact of immobilization of the defect‐bearing extremity on the development of SAP. A hole 1.2 mm in diameter was drilled in the diaphysis of the left tibia of female rats. In the experimental group (n= 15), a knee tenotomy was performed in the defect‐bearing left hind leg. We examined both femora, both tibiae, and the fourth lumbar vertebra by computed x‐ray densitometry on day 7 postoperatively. Immobilization of the defect‐bearing limb led to a decrease in x‐ray density not only of the immobilized (plt; 0.0001) but also of the contralateral tibia (plt; 0.0001). Both femora (plt; 0.001) and the fourth lumbar vertebra (plt; 0.025) of the experimental group also showed a significant decrease in x‐ray density. We previously showed that SAP leads to an increase in x‐ray density of both femora. This increase is no longer detectable in animals after immobilization of the defect‐bearing limb. Thus we conclude that immobilization interferes with SAP. This suggests the possible dependence of SAP on mechanical load. Furthermore, these data suggest a possible impact of local immobilization on the rest

ISSN:0884-0431    

DOI:10.1002/jbmr.5650071411

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1992

数据来源: WILEY