摘要:

AbstractPrevious reports on osteosarcomas treated with multi‐agent chemotherapy have shown that P‐glycoprotein expression is a reliable prognostic indicator. The current thinking is that, of the several agents used for the treatment of osteosarcoma, only doxorubicin is involved in drug resistance mediated by P‐glycoprotein. This study examines the relationship of P‐glycoprotein expression to clinical outcome in osteosarcomas, treated only with doxorubicin in addition to surgery, to determine if the prognostic significance of P‐glycoprotein expression reflects the ability of osteosarcoma to respond to this drug. The expression of P‐glycoprotein in tumor specimens was assessed by immunohistochemistry in 37 nonmetastatic, operable osteosarcomas treated at a single institution with doxorubicin as a single adjuvant drug. The P‐glycoprotein status was analysed in relation to the length of event‐free survival. A widespread pattern of P‐glycoprotein expression in tumor cells at diagnosis was significantly associated with a higher rate of systemic relapse (p<0.001). On comparison of this group of patients with a similar series of 92 patients, all treated with multi‐agent chemotherapy plus surgery of the primary lesion and previously analysed for P‐glycoprotein status, only P‐glycoprotein‐positive, doxorubicin‐resistant tumors consistently benefited from the addition of drugs other than doxorubicin (p<0.001). Osteosarcomas with different abilities to respond to adjuvant chemotherapy can be identified by the expression of P‐glycoprotein in tumor cells at the clinical onset. P‐glycoprotein status may serve as a basis for risk‐adapted, individualized therapeutic regimens. Standard programs are sufficient for P‐glycoprotein‐negative osteosarcomas, whereas P‐glycoprotein‐positive tumors may benefit from the use

ISSN:0736-0266    

DOI:10.1002/jor.1100170502

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

年代:1999

数据来源: WILEY

摘要:

AbstractOsteosarcoma, fibrous dysplasia, and myositis ossificans contain osteoid‐producing cells that are not necessarily morphologically typical osteoblasts. Nevertheless, these pathologic cells may share differentiation steps with osteoblasts at the molecular level. Osteocalcin, a bone‐specific extracellular matrix protein, is a marker of mature osteoblasts.Osteocalcinis upregulated by the transcription factor core‐binding factor alpha 1, which is responsible for commitment to the osteoblastic lineage, and is downregulated by MSX2, a homeobox‐containing transcription factor expressed during the early proliferative phase of osteoblast differentiation. Semiquantitative reverse transcription‐polymerase chain reaction was used to compare expression levels ofosteocalcin, core‐binding factor alpha 1, andMSX2in 34 osteosarcoma, five fibrous dysplasia, and five myositis ossificans specimens, as well as in seven normal cortical bone samples. Despite normal or elevated levels ofcore‐binding factor alpha‐1expression in most specimens, osteocalcin expression was low or undetectable in most cases of osteosarcoma (25 of 34) and myositis ossificans (4 of 5). Single‐strand conformation polymorphism and sequencing did not identify and mutations in the DNA‐binding domain ofcore‐binding factor alpha 1. However, a high level ofMSX2expression was demonstrated in these lesions, which may inhibitosteocalcintranscription. The presence of moderate levels of osteocalcin in fibrous dysplasia may contribute to the characteristic disconnected appearance of trabeculae in that entity because osteocalcin is a negative regula

ISSN:0736-0266    

DOI:10.1002/jor.1100170503

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

年代:1999

数据来源: WILEY

摘要:

AbstractFunctional loading provides a site‐specific signal for the regulation of bone mass and morphology. To determine if strain can inhibit the resorptive component of bone remodeling, osteoclast formation was assessed in marrow cultures plated on flexible membranes subjected to 5% strain for 10 cycles/minute, 24 hours per day. Cultures strained during days 2 through 7 inhibited osteoclast formation to 61 ± 7% of control cultures (P<0.05), a degree of inhibition similar to that observed when the cultures were subjected to strains during only days 2 through 4 but also evaluated on day 7 (67 ± 4% of control; p<0.05). In contrast, straining of cultures during days 5 through 7 had little influence on inhibiting the formation of osteoclasts (94 ± 5% of control; no significant difference). The nonuniformly strained substrate was subdivided into three concentric rings, and cultures were used to examine the site‐specificity of the inhibition caused by strain. Osteoclast formation in the outermost boundary, Which was distended from 3.6 to 5%, was 41 ± 7% of that observed in outer regions of control wells. The inhibitory potential of mechanical strain was reduced within the middle ring (73 ± 6% of control osteoclasts: p<0.01). where the strain ranged from 0.2 to 3.6%. The central region, which experienced strains equivalent to those in the middle ring (0.2 to ‐4% strain), showed inhibition of osteoclast formation to a similar degree (75 ± 6% of control). Media harvested from strained cultures failed to inhibit osteoclast formation in unstrained cultures; this implies that the inhibitory effect of strain depended on the direct interaction of the cell with the substrate rather than by a humoral factor. A second device, where a uniform strain was delivered at 1.8% throughout the entire plate, inhibited osteoclast recruitment to 48 ± 3.6%, emphasizing that uniform strain in the absence of shear stress constrains osteoclast recruitment. Thesein vitroexperiments can but model the complex environment generated byin vivomechanical strains; however, they provide the first direct evidence that strain must be considered as inhibitory to osteoclast

ISSN:0736-0266    

DOI:10.1002/jor.1100170504

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

年代:1999

数据来源: WILEY

摘要:

AbstractEndochondral growth and ossification, the processes by which cartilage increases in size and is replaced by bone, are affected by biological factors such as intrinsic genetic makeup and systemic chemical agents. In addition, these processes are affected by epigenetic mechanical factors: they may be accelerated in regions of intermittent high shear stress and decelerated in regions of intermittent high hydrostatic pressure. Previous models of bone development have not incorporated both biological and mechanobiological influences on endochondral growth and ossification. We have implemented a finite element analysis to model a developing bone rudiment from 8 weeks of gestational development to approximately 2 years after birth. As a function of time, we calculated a maturity index that reflects the progression of a region of cartilage through the endochondral ossification sequence of proliferation, hypertrophy, mineralization, and replacement by bone. We calculated a specific growth rate for each region of cartilage and estimated overall longitudinal growth of the rudiment. Regions of cartilage replaced by bone were remodeled. The results from the maturity index can be compared with distributions of proliferative, hypertrophic, and mineralized cartilage seen on histology at various stages in development. The results of the simulation predicted prenatal and postnatal developmental events, including formation of a secondary ossific nucleus, a layer of articular cartilage, and a growth plate. Our results demonstrate the necessity to include biological and mechanobiological influences when endochondral growth and ossification are considered.

ISSN:0736-0266    

DOI:10.1002/jor.1100170505

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

年代:1999

数据来源: WILEY

摘要:

AbstractAn appropriate animal model is required for the study of treatments that enhance bone healing. A new segmental long bone defect model was developed for this purpose, and dual energy x‐ray absorptiometry was used to quantify healing of this bone defect. In 15 sheep, a 3‐cm segmental defect was created in the left tibia and fixed with an interlocking intramedullary nail. In seven animals, the defect was left empty for the assessment of the spontaneous healing response. In eight animals serving as a positive control, autologous bone grafting was performed. After 12 weeks, healing was evaluated with radiographs, a torsional test to failure, and dual energy x‐ray absorptiometry. The mechanical test results were used for the assessment of unions and nonunions. Radiographic determination of nonunion was not reliably accomplished in this model. By means of dual energy x‐ray absorptiometry, bone mineral density and content were measured in the middle of the defect. Bone mineral density was 91 ± 7% (mean ± SEM) and 72 ± 6% that of the contralateral intact tibia in, respectively, the autologous bone‐grafting and empty defect groups (p = 0.04). For bone mineral content, the values were, respectively, 117 ± 18 and 82 ± 9% (p = 0.07). Torsional strength and stiffness were also higher, although not significantly, in the group with autologous bone grafting than in that with the empty defect. Bone mineral density and content were closely related to the torsional properties (r2ranged from 0.76 to 0.85, p ⩽ 0.0001). Because interlocking intramedullary nailing is a very common fixation method in patients, the newly developed segmental defect model has clinical relevance. The interlocking intramedullary nail provided adequate stability without implant failure. This model may be useful for the study of treatments that affect bone healing, and dual energy x‐ray absorptiometry may be somewhat helpful in the analysis of healing o

ISSN:0736-0266    

DOI:10.1002/jor.1100170506

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

年代:1999

数据来源: WILEY

摘要:

AbstractHip fracture among the elderly is a large and growing public health issue. Presently, all therapies approved for treatment and prevention of osteoporosis involve pharmacological agents that act systemically. In this study, we evaluated the feasibility of preventing osteoporotic hip fractures with local, rather than systemic, therapy. Our hypothesis is that local therapy to increase bone density may be as effective as systemic therapy in reducing fracture risk. Thus, the goal of this investigation was to use finite element analyses to study the effect of a localized increase in bone density on the strength of an osteopenic, human femur. Finite element predictions of the failure load were made after increasing the bone density within small regions in the proximal femur. The outcome variable from these analyses was the predicted load required to break a femur in a simulated fall to the side with impact on the greater trochanter. Increasing the density by 25% relative to baseline values in a small region (0.86 cm3) of the femoral neck increased the predicted failure load by 6.2%. The same density increase in a much larger region (4.92 cm3) increased the failure load by 15%. Inclusion of more than one region of increased density provided little additional benefit. In comparison, when the density of the entire femur was increased by 5% relative to baseline values, the predicted failure load increased by 5.4%. These findings suggest that agents capable of inducing increased bone density in small regions of the proximal femur have the potential to reduce the risk of hip fracture.

ISSN:0736-0266    

DOI:10.1002/jor.1100170507

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

年代:1999

数据来源: WILEY

摘要:

AbstractPeriosteum provides a source of undifferentiated chondrocyte precursor cells for fracture healing that can also be used for cartilage repair. The quantity of cartilage that can be produced, which is a determining factor in fracture healing and cartilage repair, is related to the number of available stem cells in the cambium layer. Cartilage formation during both of these processes is enhanced by motion of the fracture or joint in which periosteum has been transplanted. The effect of dynamic fluid pressure on cell proliferation in periosteal tissue cultures was determined in 452 explants from 60 immature (2‐month‐old) New Zealand White rabbits. The explants were cultured in agarose suspension for 1‐14 days. One group was subjected to cyclic hydrostatic pressure, which is referred to as dynamic fluid pressure, at 13 kPa and a frequency of 0.3 Hz. Control explants were cultured in similar chambers without application of pressure. DNA synthesis ([3H]thymidine uptake) and total DNA were measured. The temporal pattern and distribution of cell proliferation in periosteum were evaluated with autoradiography and immunostaining with proliferating cell nuclear antigen. Dynamic fluid pressure increased proliferation of periosteal cells significantly, as indicated by a significant increase in [3H]thymidine uptake at all time points and a higher amount of total DNA compared with control values. On day 3, when DNA synthesis reached a peak in periosteal explants, [3H]thymidine uptake was 97.000 ± 5.700 dpm/μg DNA in the group exposed to dynamic fluid pressure and 46,000 ± 6,000 dpm/μg in the controls (p<0.001). Aphidicolin, which blocks DNA polymerase α, inhibited [3H]thymidine uptake in a dose‐dependent manner in the group subjected to dynamic fluid pressure as well as in the positive control (treated with 10 ng/ml of transforming growth factor‐β1) and negative control (no added growth factors) groups, confirming that [3H]thymidine measurements represent proliferation and dynamic fluid pressure stimulates DNA synthesis. Total DNA was also significantly higher in the group exposed to dynamic fluid pressure (5,700 ± 720 ng/mg wet weight) than in the controls (3,700 ± 630) on day 3 (p<0.01). Autoradiographs with [3H]thymidine revealed that one or two cell cycles of proliferation took place in the fibrous layer prior to proliferation in the cambium layer (where chondrocyte precursors reside). Proliferating cell nuclear antigen immunophotomicrographs confirmed the increased proliferative activity due to dynamic fluid pressure. These findings suggest either a paracrine signaling mechanism between the cells in these two layers of the periosteum or recruitment/migration of proliferating cells from the fibrous to the cambium layer. On the basis of the data presented in this study, we postulate that cells in the fibrous layer respond initially to mechanical stimulation by releasing growth factors that induce undifferentiated cells in the cambium layer to divide and differentiate into chondrocytes. These data indicate that cell proliferation in the early stages of chondrogenesis is stimulated by mechanical factors. These data indicate that cell proliferation in the early stages of chondrogenesis is stimulated by mechanical factors. These findings are important because they provide a possible explanation for the increase in cartilage repair tissue seen in joints subjected to continuous passive motion. The model ofin vitroperiosteal chondrogenesis under dynamic fluid pressure is valuable for studying the mechanisms by which mechanical factors might be involved in the formation of cartilage in the early fracture callus and during

ISSN:0736-0266    

DOI:10.1002/jor.1100170508

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

年代:1999

数据来源: WILEY

摘要:

AbstractMajor loss of tissue is an almost invariable consequence of severe closed soft‐tissue injury. Clinically, the extent of soft‐tissue trauma determines the outcome of complex injuries and significantly influences bone healing. With use of a new animal model, this study quantitatively analyzed microcirculation, i.e., nutritive perfusion and leukocyte‐endothelial cell interaction, in skeletal muscle after standardized closed soft‐tissue injury. By means of a computer‐assisted controlled‐impact technique, a severe standardized closed soft‐tissue injury was induced in the left hindlimb of 28 rats. The rats were assigned to four experimental groups (n = 7 per group) that differed by time of analysis (1.5, 24, 72, and 120 hours after injury); rats that were not injured served as controls (n = 7). Intramuscular pressure was measured, and microcirculation in the rat extensor digitorum longus muscle was analyzed byin vivofluorescence microscopy, which allowed assessment of microvascular diameters, functional capillary density, number of rolling and adherent leukocytes in venules, and microvascular permeability. Edema weight gain was quantified by the ratio of wet to dry weight of the extensor digitorum longus muscle. Microvascular perfusion of the skeletal muscle was characterized by a significant reduction in functional capillary density, which was paralleled by an increase in capillary diameter throughout the 120 hours of observation when compared with the controls. Traumainduced inflammatory response was reflected by a markedly increased rolling and adherence of leukocytes, primarily restricted to the endothelium of postcapillary venules; this was accompanied by increased microvascular permeability, indicative of a substantial loss of endothelial integrity. The microcirculation surrounding the core of the damaged tissue area resembled that of ischemia‐reperfusion injury in skeletal muscle, i.e., heterogeneous capillary perfusion, pronounced microvascular leakage and adherence of leukocytes. Enhanced vascular leakage and leukocyte adherence (24‐72 hours after injury) coincided with the maximum intramuscular pressure (which was not indicative of compartment syndrome) and edema formation. These results demonstrate that initial changes, leading to ultimate tissue death, after closed soft‐tissue injury are caused on the microcirculatory level. This standardized model provides further insight into microvascular pathophysiology and cellular interactions following closed soft‐tissue injury. Thus, it is an adequate tool for testing novel ther

ISSN:0736-0266    

DOI:10.1002/jor.1100170509

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

年代:1999

数据来源: WILEY

摘要:

AbstractPeriprosthetic bone loss is an important contributory factor for aseptic loosening of total joint replacements. It has recently been shown that osteoclast precursor cells are present in the wear particle‐associated macrophage infiltrate found in the membrane surrounding loose implants and that these cells are capable of differentiating into osteoclastic bone‐resorbing cells. Long‐term co‐culture of arthroplasty‐derived macrophages and the rat osteoblast‐like cell line, UMR‐106, in the presence of 1,25 (OH)2D3results in the formation of numerous multinucleated cells that are positive for tartrate‐resistant acid phosphatase and vitronectin receptor and capable of extensive lacunar bone resorption. The aim of this study was to determine the effect of cytokines/growth factors, known to be present in the arthroplasty membrane, on this process of osteoclast differentiation. During osteoclast formation, increased levels of macrophage colony‐stimulating factor, interleukin‐6, and to a lesser extent, interleukin‐1β, but not tumour necrosis factor α, were detected in the co‐culture supernatants. Addition of neutralising antibodies to human interleukin‐1β or tumour necrosis factor α to the co‐culture system did not inhibit osteoclast formation. In contrast, co‐cultures to which neutralising antibodies to human macrophage colony‐stimulating factor or interleukin‐6 were added contained fewer cells positive for tartrate‐resistant acid phosphatase and vitronectin receptor and formed significantly fewer resorption pits. Time‐course studies showed that macrophage colony‐stimulating factor and interleukin‐6 increase osteoclast formation mainly in the early stages of osteoclast differentiation. These results indicate that the release of macrophage colony‐stimulating factor and interleukin‐6 by activated cells in the arthroplasty membrane is likely to contribute to pathological bone resorption associated with aseptic loosening by stimulating differentiation of mononuclear phagocyte osteo

ISSN:0736-0266    

DOI:10.1002/jor.1100170510

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

年代:1999

数据来源: WILEY

摘要:

AbstractPolyethylene wear of the acetabular component can be described as one or more vectors. To help clarify the mechanisms of wear advancementin vivo, we used a combination of retrieved implants and radiographs to describe the three‐dimensional wear vectors in total hip arthroplasty. The wear vectors in 41 retrieved implants from a single manufacturer were measured with use of the shadowgraph technique, and the spatial orientation of each implant was calculated from serial anteroposterior pelvic radiographs. On the basis of the combination of the wear vector in the implant and implant orientation in the pelvis, the wear vectorsin vivowere determined. The mean wear vector was directed 8.1° lateral in the coronal plane and 4.1° posterior in the sagittal plane. The wear vectorin vivoshowed a relatively wide range of directions, not necessarily coinciding with the commonly presumed resultant force in the hip. The wear vectors were not associated with the spatial orientation of the acetabular components, but cups with impingement demonstrated more anterior wear than did those without impingement. Our results suggest that the process of polyethylene wear is not as simple as previously described and that several factors influence advancement of wearin v

ISSN:0736-0266    

DOI:10.1002/jor.1100170511

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

年代:1999

数据来源: WILEY