ISSN:0736-0266    

DOI:10.1002/jor.1100170302

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

年代:1999

数据来源: WILEY

ISSN:0736-0266    

DOI:10.1002/jor.1100170303

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

年代:1999

数据来源: WILEY

摘要:

AbstractThirty patients with gonarthrosis were operated on with the PCA primary total knee prosthesis and had the tibial component fixed to the bone by partial cementation. In the first two groups of patients, cementation was by a peripheral rim of high and low‐viscosity cement, respectively. In the third group, the pegs were cemented with the low‐viscosity cement. Follow‐up was performed with use of clinical parameters and roentgen stereophotogrammetric analysis. Clinically, the series was successful apart from a problem with tibial component wear, necessitating revision in five patients. At 8 years, the mean Hospital for Special Surgery score was 81 points. Venn‐diagram scores revealed four failures and three acceptable cases; the remaining cases were satisfactory. Apart from one loose patellar component, there was no mechanical loosening. Roentgen stereophotogrammetric analysis showed that the tibial components moved relative to the bone; this indicated fibrous tissue fixation. which was corroborated histologically in two patients. The objective, to achieve bone ingrowth, was thus not successfully met. Radiolucent lines were consistently seen, and their size correlated with the migration as measured by roentgen stereophotogrammetric analysis. Furthermore, five continuously migrating prostheses showed significantly larger radiolucent zones than the prostheses that migrated only initially, and they were less well bonded to the bone at 1 year. In conclusion, partial cementation does not appear to be a way to achieve bone ingrowth in porous‐coated implants u

ISSN:0736-0266    

DOI:10.1002/jor.1100170304

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

年代:1999

数据来源: WILEY

摘要:

AbstractMechanical debonding of the stem/cement interface has been implicated in the failure process of cemented femoral hip components. The nature of this failure process remains poorly understood due, in part, to limited understanding of how interfacial debonding occurs in response to a wide range of loading conditions. The purpose of this investigation was to determine the fracture toughness of the cobalt‐chromium alloy/polymethylmethacrylate interface under mixed‐mode loading conditions. The hypothesis was that the critical energy release rate was dependent on the phase angle of the crack tip and that the fracture response would be significantly different for a smooth compared with rough interface surface. A novel in‐plane shear test fixture was developed with use of a combination of finite element and experimental fracture‐mechanics tests. A wide range (−65–60°) of phase angles was determined with the in‐plane shear test and a clamped cantilever‐beam test. Sixty experimental tests were performed for cobalt‐chromium alloy bars with a plasma‐sprayed coating or a precoat of polymethylmethacrylate over a satin‐finished surface. For the specimens with the plasma‐sprayed coating, critical energy release rates (500–700 J/m2) were not a function of the phase angle of the crack tip. In contrast, critical energy release rates (15–80 J/m2) were found to be strongly affected by the phase angle for the specimens precoated with polymethylmethacrylate. The critical energy release rate for specimens with the plasma‐sprayed surface was significantly (p<0.01) greater than for those precoated with polymethylmethacrylate. The critical energy release rate increased markedly with the phase angle of the crack tip for the specimens precoated with polymethylmethacrylate. The results suggest that the failure response of a stem with a plasma‐sprayed surface may be insensitive to the loading angle of the crack tip, whereas a stem precoated with polymethylmethacrylate may be more likely to debo

ISSN:0736-0266    

DOI:10.1002/jor.1100170305

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

年代:1999

数据来源: WILEY

摘要:

AbstractOrthopaedic surgeons must currently choose from several types of ultra high molecular weight polyethylene acetabular cups that differ in their material properties and in the methods used for their sterilization. Information on the wear resistance of these different cups may help in the selection process. This study included two separate tests for wear run on a hip simulator to investigate the effect of molecular weight, calcium stearate, and sterilization methods on the wear resistance of ultra high molecular weight polyethylene acetabular cups. Test 1 revealed nearly identical wear rates for acetabular cups with molecular weights in two distinct ranges, as well as for cups with molecular weights in the same range but with or without calcium stearate added. In Test 2, cups that were sterilized in air with gamma irradiation exhibited lower rates of wear than those sterilized with ethylene oxide, presumably due to the crosslinking induced by the irradiation. In addition, cups that were irradiated while packed in a partial vacuum to minimize oxygen absorbed in the surface layer initially showed lower rates of wear than those irradiated in air, with the wear rates becoming similar as wear penetrated the more oxidized surface layer and the more crosslinked subsurface region. Because these tests were run a few months after the irradiation, the potential effects of long‐term oxidation of any residual free radicals in the irradiated materials could not be taken into account. After artificial aging to accelerate oxidative degradation of the materials, the wear rates could be markedly different. Analyses performed after wear indicated that the irradiated (i.e., crosslinked) cups exhibited a smaller proportion of, as well as shorter, fibrils in the wear debris and an increased crystallinity and melting temperature and that gamma irradiation in the low‐oxygen environment reduced the level of oxidation and increased the level of crosslinking in the surface region of the c

ISSN:0736-0266    

DOI:10.1002/jor.1100170306

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

年代:1999

数据来源: WILEY

摘要:

AbstractPrevious studies indicate that modification of the surface of porous bioactive glass promotes osteoblast function. We hypothesize that bone formation on treated bioactive glass is due to the selective adsorption of serum attachment proteins. To test this hypothesis, we examined the profile of proteins adsorbed to treated bioactive glass and compared these proteins with those adsorbed to untreated bioactive glass and porous hydroxyapatite. Porous bioactive glass was treated with Tris‐buffered electrolyte solution to generate a calcium phosphate‐rich surface layer and then immersed in tissue‐culture medium containing 10% serum. Proteins adsorbed to the ceramic surfaces were analyzed by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis and Western blot analysis. Porous hydroxyapatite bound a higher amount of total protein than did the other substrates. However, surface‐modified porous bioactive glass adsorbed more fibronectin than did hydroxyapatite. The effect of serum‐protein adsorption on osteoblast adhesion to bioactive glass and hydroxypatite was also evaluated. Cell adhesion to porous bioactive glass that was either surface‐modified and serum‐treated was significantly greater than to porous bioactive glass that was either surface‐modified or serum‐treated. Furthermore, cell adhesion to porous bioactive glass treated to form the dual layer of calcium phosphate and serum protein was significantly higher than adhesion to porous hydroxyapatite with adsorbed serum protein. Results of the study strongly suggest that adsorption of serum fibronectin to the surface of modified porous bioactive glass coated with calcium phosphate may be responsible for enhanced

ISSN:0736-0266    

DOI:10.1002/jor.1100170307

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

年代:1999

数据来源: WILEY

摘要:

AbstractWith the etiology of osteoporotic fractures as motivation, the goal of this study was to characterize the mechanical behavior of human trabecular bone after overloading. Specifically, we quantified the reductions in modulus and strength and the development of residual deformations and determined the dependence of these parameters on the applied strain and apparent density. Forty cylindrical specimens of human L1 vertebral trabecular bone were destructively loaded in compression at 0.5% strain per second to strains of up to 3.0% and then immediately unloaded to zero stress and reloaded. (An ancillary experiment on more readily available bovine bone had been performed previously to develop this testing protocol.) In general, the reloading stress‐strain curve had a short initial nonlinear region with a tangent modulus similar to Young's modulus. This was followed by an approximately linear region spanning to 0.7% strain, with a reduced residual modulus. The reloading curve always approached the extrapolated envelope of the original loading curve. Percent modulus reduction (between Young's and residual), a quantitative measure of mechanical damage, ranged from 5.2 to 91.0% across the specimens. It increased with increasing plastic strain (r2= 0.97) but was not related to modulus or apparent density. Percent strength reduction, in the range of 3.6–63.8%, increased with increasing plastic strain (r2= 0.61) and decreasing apparent density (r2= 0.23). The residual strains of up to 1.05% depended strongly on applied strain (r2= 0.96). Statistical comparisons with previous data for bovine tibial bone lend substantial generality to these trends and provide an envelope of expected behavior for other sites. In addition to providing a basis for biomechanical analysis of the effects of damage in trabecular bone at the organ level, these findings support the concept that occasional overloads may increase the risk of fracture by substantially degrading the mechanical properties of the underlying trabecular b

ISSN:0736-0266    

DOI:10.1002/jor.1100170308

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

年代:1999

数据来源: WILEY

摘要:

AbstractAnin vivoanimal model of bone adaptation was used to examine a possible role for matrix metalloproteinase‐1 in the local mediation of bone remodeling: to corrode the coupling of osteocytes to the matrix in an attempt to autoregulate the cell's perception of its mechanical environment. Twelve young (12–16 months old) skeletally mature turkeys were separated into groups to be studied for stimulus periods of either 3 or 30 days. In each animal, the left ulna was functionally isolated and subjected to either disuse or 3,000 microstrain at 1 Hz for 10 minutes per day. The right ulna remained intact and served as an intra‐animal control. No significant differences in bone area were detected at 3 days; however, ulnae subjected to disuse lost 8 ± 4% (±SD) of bone area by 30 days. Over the same period, ulnae subjected to the mechanical stimulus gained 21 ± 9% of bone area. With use ofin situreverse transcription‐polymerase chain reaction, less than 2% of the osteocytes examined from the intact control ulnae stained positively for matrix metalloproteinase‐1 mRNA. An antibody raised against matrix metalloproteinase‐1 revealed no positively labeled osteocytes in the intact ulnae. This low percentage of osteocytes expressing matrix metalloproteinase‐1 mRNA was similar to that seen in ulnae subjected to the osteogenic mechanical stimuli. In contrast, ulnae subjected to either 3 or 30 days of disuse showed evidence of matrix metalloproteinase‐1 mRNA activity in a high percentage of osteocytes (89 ± 5 and 66 ± 8%, respectively; each time point significantly different from intact ulnae, as well as from each other, p<0.05). The percentage of osteocytes labeled with the anti‐matrix metalloproteinase‐1 antibody was also highly elevated following 3 days of disuse (74 ± 17%). These data demonstrate that an early response of bone to disuse is the upregulation of matrix metalloproteinase‐1 activity in osteocytes. It is proposed that this upregulation of collagenase activity is indicative of the cell's degradation of coupling to the matrix, and it thus reflects the osteocyte's regulation of its own mechanical environment. We believe that such autoregulation of the osteocyte's physical environment will accommodate subtle changes in the bone's functional environment without the need t

ISSN:0736-0266    

DOI:10.1002/jor.1100170309

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

年代:1999

数据来源: WILEY

摘要:

AbstractThis study investigated the angiogenic response to four varying rates (0.3, 0.7, 1.3, and 2.7 mm/day) of distraction in a rabbit model of leg‐lengthening. Immunostaining was performed with use of specific antibodies to type‐IV collagen and endothelial cell antigen to examine semiquantitatively the presence of blood vessels in the developing tissues. With use of the Chalkley counting method, the greatest number of positive staining blood vessel cells was found in the central fibrous zone of the groups that underwent lengthening at 0.7 and 1.3 mm/day compared with any other zone in any group (p<0.05,ttest). There were no statistical differences in the positive labeling indices in the mineralization front and the new bone zone adjacent to the mineralization front in any of the groups. However, the decrease in the number of positive‐staining blood vessel cells in the new bone zone distant to the mineralization front compared with any other zone in any group was statistically significant. The results suggest that during distraction osteogenesis, the precursor cells of new capillaries were present in abundance within the fibrous interzone. These cells connected into the capillary network at the junction of the mineralization front and the fibrous zone. The angiogenic response was weaker in the more mature regions within the new bone zones. A slow rate of distraction (0.3 mm/day) did not maximally stimulate angiogenesis in the central fibrous zone, whereas high rates (2.7 mm/day) appeared to impair this response. In this model of distraction osteogenesis, the vascularization process in the central fibrous zone was maximally stimulated at distraction rates of 0.7 and 1.3 m

ISSN:0736-0266    

DOI:10.1002/jor.1100170310

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

年代:1999

数据来源: WILEY

摘要:

AbstractThe laser speckle method is a new form of flowmetry that can obtain a two‐dimensional distribution of blood flow in tissue. This method is a noncontact, simple, and rapid technique that may aid in the diagnosis of osteonecrosis. We investigated whether the subchondral bone blood flow within the femoral condyles of rabbits could be measured by the laser speckle method. The hydrogen washout method was chosen as a comparison technique because of its ability to allow repetitive measurements of blood flow in various conditions in one rabbit and because of its realiability which already has been established. We simultaneously measured the bone blood flow in 20 femoral condyles of 10 rabbits with the laser speckle and hydrogen washout methods and found a significant correlation between the blood flow levels with use of these two methods. For the clinical application of the laser speckle method, we also investigated the influence of cartilage thickness on the measurements and the depth in the bone to which blood flow could be measured with this method. A cartilage thickness of 0.2 mm did not influence the measurement of the bone blood flow, and the depth in the bone to which the laser speckle method could be used was approximately 2 m

ISSN:0736-0266    

DOI:10.1002/jor.1100170311

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

年代:1999

数据来源: WILEY