Combined effects of FK506 (tacrolimus) and cyclophosphamide on atypical B220+ T cells, cytokine gene expression and disease activity in MRL/MpJ-lpr/lpr mice

Groups of female MRL/MpJ-lpr/lpr mice received either saline or FK506 (tacrolimus; 2 mg/kg intraperitoneally) three times weekly, cyclophosphamide (CY; 20 mg/kg) once monthly, or both drugs from 8 weeks of age. Median survival for untreated and CY-treated mice was 26 weeks, and for FK506- and FK506 + CY-treated groups was > or = 44 weeks. Severity of skin lesions and lymph node hyperplasia was markedly reduced by the drug combination, whereas either drug alone was less effective. FK506 or CY alone delayed the onset of proteinuria, but by 24 weeks all of these animals were positive. In contrast, drug combination reduced the prevalence of proteinuria to < or = 60% throughout the 44 weeks of study. Sequential monitoring of peripheral blood lymphocytes revealed that combination therapy but not monotherapy markedly reduced the proportion of atypical CD3+ B220+ and CD3+CD4-CD8- T cells. Neither FK506 nor CY affected the reduction in IL-2 and IL-4 mRNA levels observed in lymph nodes of diseased animals compared with normals. Although the drug combination also did not affect IL-2 mRNA levels, IL-4 mRNA transcripts were increased six-fold compared with saline-treated controls. IL-10 and interferon-gamma (IFN-gamma) mRNAs were induced by FK506, CY and by the drug combination. Serum levels of anti-dsDNA antibodies were reduced in all treatment groups. These data demonstrate improved efficacy of combined T and B cell-directed immunosuppression in murine lupus, associated with marked inhibition of atypical T cells and selective augmentation of IL-4 within the affected lymphoid tissue.

Cyclic compressive loading results in fatigue cracks in ultra high molecular weight polyethylene

Wear damage to the articulating surfaces of total joint components made of ultra high molecular weight polyethylene is associated with a fatigue fracture mechanism, despite the fact that these surfaces are subjected to primarily compressive and compressive-tensile cyclic stresses. The question arises as to whether fatigue cracks will form under such loading conditions. In this study, we experimentally demonstrated that fatigue cracks could be initiated and propagated in notched ultra high molecular weight polyethylene specimens subjected to fully compressive and compressive-tensile cyclic loading. Under these loading conditions, growth of fatigue cracks was limited: the cracks arrested without catastrophic failure of the test specimens. The final length of the crack was dependent on the load ratio of the fatigue cycle; fatigue cracks propagated to greater lengths as the load ratio was increased.

The natural history of ultra high molecular weight polyethylene

Degradative changes occurring during the lifetime of ultra high molecular weight polyethylene total joint components made from 2 different starting resins were determined from retrieved tibial inserts. The inserts were manufactured in the Department of Biomechanics of the authors' institution, for intrahospital use by the hospital's surgical staff, allowing the ultra high molecular weight polyethylene properties to be traced from production, to sterilization, to shelf life, and to subsequent retrieval. Changes were found in the density and the infrared spectra. Density was greater after sterilization and at retrieval, when compared with the density of the virgin ultra high molecular weight polyethylene material, with a greater increase near the surfaces than within the bulk of the inserts. The inserts that had the longest life-times demonstrated the greatest increase in density. Density increases are important because they reflect increases in the elastic modulus of the ultra high molecular weight polyethylene. Such increases near the articulating surface of a total joint component would cause significant increases in the stresses associated with wear damage occurring on and near these surfaces. The infrared spectra were consistent with oxidative degradation.

Fatigue testing of cerclage stainless steel wire fixation

Because wire fixation continues to be used extensively in the practice of orthopaedic surgery, despite a high incidence of wire breakage, understanding the mechanism of this failure is of important clinical interest. The aim of this study was to investigate the failure of cerclage stainless steel wire using an in vitro cyclic loading device. A stainless steel testing fixture consisting of two half cylinders with a combined diameter of 2.5 cm was mounted in a servo hydraulic testing machine. Specimens of number 18 gauge (0.97 mm diameter) and number 16 gauge (1.22 mm diameter) 316L stainless steel wire were mounted around the two half cylinders in a cerclage manner using three different fastening methods: a uniform symmetrical twist, a knot twist, and a square knot. Single-load-to-failure and cyclic load tests were performed under controlled tensile displacement. The cerclage wire system fastened with a twist resulted in failure at loads significantly lower than systems fastened with the knot twist and the square knot. Cyclic loading of the wire fastened with twists also showed decreased fatigue properties when compared to those fastened with the knot twist and the square knot. In all tests, the 16-gauge wire was found to be clearly superior to the 18-gauge wire. For both wires, fatigue strengths at 100,000 cycles were only 30-37% of the static ultimate strength. These results show that wire diameter and fastening system are two important factors affecting the mechanical properties of the resulting fixation.

Post-irradiation aging of ultra-high molecular weight polyethylene

A study was performed to determine the time-course of oxidative degradation and the extent to which the degradation proceeded through the bulk of ultra-high molecular weight polyethylene joint components that had been irradiated and stored on a shelf. Standardized cylindrical samples, taken from a single batch of extruded polyethylene, were cleaned, packaged, and sterilized according to protocols used for commercial joint-replacement components. After sterilization, the samples were stored in the packages for time-periods of one day to more than one year. At each interval studied, thin sections were cut as a function of depth into the bulk of the sample and were used to determine the density and the infrared spectra. Marked alterations in the density and the infrared spectra consistent with continuing oxidative degradation occurred throughout the year of storage on the shelf. The alterations were most severe near the surface of the samples.

Fatigue crack propagation behavior of ultra high molecular weight polyethylene under mixed mode conditions

Analytical studies of the stresses on and within ultra high molecular weight polyethylene joint components suggest that damage modes associated with polyethylene fatigue failure are caused by a combination of surface and subsurface crack propagation. Fatigue crack propagation tests under mixed mode loading conditions were conducted on center-cracked tension specimens machined from extruded blocks of sterilized polyethylene in an attempt to determine how fatigue cracks change direction in this material. Cyclic testing was performed using a sinusoidal wave form at a frequency of 5 Hz and an R-ratio (minimum load/maximum load) of 0.15. Specimens had the notch oriented perpendicular to the direction of applied load and at angles of 60 degrees and 45 degrees to the loading direction. Numerical analyses were used to interpret the experimental test and to predict the fatigue behavior of polyethylene under mixed mode conditions. It was found that all cracks eventually propagated horizontally, regardless of the initial angle of inclination of the notch to the direction of applied cyclic load. In fact, the extent of the curvilinear crack growth was quite limited. An effective range of cyclic stress intensity factor was calculated for correlation with the rate of crack growth. The results followed a Paris relation, with crack growth rate linearly related to a power of the range of stress intensity, for all three crack orientations. The numerical analyses adequately modeled the experimental fatigue crack growth results.

A unique palindromic element mediates gamma interferon induction of mig gene expression

To define the molecular mechanisms involved in the action of gamma interferon (IFN-gamma), we have analyzed the transcriptional regulation of the mig (monokine induced by gamma interferon) gene, a member of the platelet factor 4-interleukin-8 cytokine family that is expressed in murine macrophages specifically in response to IFN-gamma. Analysis of mig/CAT chimeric constructs transiently transfected into the RAW 264.7 mouse monocytic cell line revealed a unique IFN-gamma-responsive element (gamma RE-1). The sequence of this cis regulatory element defined by deletion analysis contains an imperfect inverted repeat extending 27 bp. Examination of mig/CAT constructs with mutations in gamma RE-1 revealed that the palindromic positions in the element were essential for activity. Consistent with its function as an enhancer, a single copy of gamma RE-1 conferred IFN-gamma inducibility to a heterologous (herpes simplex virus thymidine kinase) promoter. Exonuclease III protection assays demonstrated symmetrical protection of a mig promoter fragment centered about the gamma RE-1 palindromic sequence. Using the gel electrophoretic mobility shift assay, we identified a factor (gamma RF-1) present in nuclear extracts prepared from IFN-gamma-stimulated RAW 264.7 cells which binds to gamma RE-1. The activation of gamma RF-1 occurred rapidly (within 1 min) in response to IFN-gamma and was independent of protein synthesis. Similar to the expression of mig mRNA, the formation of gamma RF-1 was selectively induced by IFN-gamma and not IFN-alpha. The regulation of gene expression through gamma RF-1 and gamma RE-1 may explain the preferential activation of a subset of interferon-inducible genes by IFN-gamma.

Dislocation following THA: comparison of two acetabular component designs

One hundred ninety-seven consecutive primary cemented total hip arthroplasties using 22 mm heads were evaluated for the rate of dislocation. All surgery was performed by one surgeon through a posterior approach. A Charnley type femoral component was used in each case. Patients were divided into three groups based on the acetabular component used. Group I had 60 Charnley HPW cups implanted between January 1985 and December 1986; group II had 70 Tibac cups implanted between January 1987 and August 1987; and group III had 67 Charnley HPW cups implanted between September 1987 and February 1988. The groups were similar with regards to age, sex, original diagnosis, and surgical technique. There was a total of 11 dislocations (5.6%), of which 8 (11.4%) occurred in group II (Tibac cup). Furthermore, 6 patients (3%) developed recurrent hip dislocations, 5 (7.1%) of which were from group II. Group II had a statistically significant increase in the dislocation rate (P < .05). The authors conclude that the dislocation rate with the 22 mm Tibac cup is unacceptably high and that the design of the Charnley cup affords greater stability to the artificial hip joint than the hemispherical design of the Tibac cup.

The effect of temperature, stress and microstructure on the creep of compact bovine bone

Creep tests of 117 compact bovine bone specimens were conducted at three temperatures (25, 37, and 43 degrees C), with applied stresses between 71 and 115 MPa. Following testing, the amount of secondary haversian bone in the gage region of the specimens was estimated. The resulting steady-state creep rates (epsilon) were fit to an Arrhenius (e-Qc/RT) model (where Qc is the activation energy for the mechanism(s) controlling creep, R is the gas constant, and T is the absolute temperature) of the type used to describe the classic steady-state creep behavior of metals, ceramics, and metamorphic rocks. The empirical model developed was epsilon = 5.6 x 10(-9) e4.6F sigma 5.2 e-5330/T, where epsilon is the estimated mean steady-state creep rate, F is the volume fraction of secondary haversian bone, sigma is the applied stress, and T is the absolute temperature. There was a positive, significant association between the estimated mean steady-state creep rate and F, sigma, and T. Qc was determined to be 44.3 kJ mol-1, a reasonable value when compared to activation energies for creep in ceramics. It is hypothesized that permanent deformation during creep of compact bovine bone is primarily due to damage mechanisms associated with dislocations in the hydroxyapatite mineral lattice structure.

Activation of phospholipase D by alpha-thrombin or epidermal growth factor contributes to the formation of phosphatidic acid, but not to observed increases in 1,2-diacylglycerol

The receptor-mediated activation of a phosphatidylcholine-hydrolysing phospholipase D (PLD) has recently been described. We investigated the effect of alpha-thrombin and epidermal growth factor (EGF) on cellular PLD activity in order to determine the role of this enzyme in mitogen-induced increases in phosphatidic acid and sn-1,2-diacylglycerol. In the presence of ethanol, stimulation of [3H]myristic acid-labelled quiescent IIC9 cells with alpha-thrombin or EGF resulted in a rapid increase in radiolabelled phosphatidyl-ethanol which reached a plateau at 1 min, indicating the rapid and transient activation of PLD. We observed a concomitant decrease in the mitogen-stimulated increase of radiolabelled phosphatidic acid. In contrast, ethanol did not significantly effect the elevation of sn-1,2-diacylglycerol levels stimulated by alpha-thrombin or EGF as determined by measurement of sn-1,2-diacylglycerol mass or the appearance of [3H]1,2-diacylglycerol. A novel lipid, detected by two-dimensional t.l.c. analysis, was generated in [3H]myristic acid-labelled cells stimulated with alpha-thrombin, but not EGF, in the presence of ethanol. Treatment in vitro of cellular lipids isolated from [3H]myristic acid-labelled cultures with PLD in the presence of ethanol also resulted in the generation of this novel lipid species, supporting the role of this enzyme in its production. These data indicate that in quiescent IIC9 cells: (a) alpha-thrombin or EGF rapidly and transiently activates a PLD; (b) although this activation is responsible for part of the mitogen-induced increases in phosphatidic acid, it does not contribute to induced increases in sn-1,2-diacylglycerol; and (c) activation of this enzyme appears to be involved in the formation of a novel lipid generated in response to alpha-thrombin, but not EGF, in IIC9 fibroblasts.

Wear of polyethylene in total joint replacements. Observations from retrieved PCA knee implants

Observations of wear damage were performed on 12 retrieved porous coated anatomic (PCA) tibial components, all of which were removed because of excessive polyethylene wear. Density measurements of the remaining polyethylene were obtained as a function of depth from the surface of the components. Comparison to previous results from similar studies of total condylar type knee components and total hip acetabular components revealed distinct differences between the types and severity of damage, emphasizing the influence of design factors on the corresponding wear damage. These results confirm previous conclusions that nonconforming articulating surfaces on thin polyethylene components will be at higher risk of damage than more conforming surfaces on thicker components. It also appears that the high cyclic loads to which polyethylene implants are subjected in vivo are most responsible for the degradation in properties of the material near the articulating surface, although the heat pressing of the articulating surface of the PCA components may contribute to the problem.

Mechanical characteristics of the stem-cement interface

The mechanical characteristics of the interface between a metallic stem and the surrounding poly(methyl methacrylate) bone cement were determined from experimental tests and finite element analyses. Push-through-stem tests of straight and tapered titanium alloy stems, surrounded by cement columns, were performed and the resulting load-displacement behavior and strain distribution on the surface of the cement column were measured for loading, unloading, and reloading. Test geometries were modelled using nonlinear, axisymmetric, finite element analyses, which incorporated Coulomb friction elements at the titanium alloy-cement interface. Initial residual stresses, due to curing of the cement column, were modeled by thermal contraction of the cement. Good agreement was obtained between load-displacement curves and surface strains predicted from the nonlinear analysis and those obtained from experiments, when a coefficient of friction of 0.3 was assumed for the stem-cement interface. These results show that, in the absence of chemical adhesion, the load-displacement behavior of a stem-cement composite can be described completely in terms of the friction at the interface and the residual stresses normal to the interface.

The biologic effects of implant materials

The interaction between implant materials and the surrounding biological environment continues to be an area of intense research and clinical interest. This article presents the information presented in a symposium, held during the 36th Annual Meeting of the Orthopaedic Research Society, in which several important issues concerning the biologic effects of implant materials were discussed. These issues included the mechanisms by which implant materials are released to the surrounding tissues and the ways in which these tissues respond to implant materials. The problem of bone loss around cementless implants was discussed as a specific example of a biologic effect resulting in both bone remodelling and endosteal erosion.

Demonstration that phosphorescent 6-bromo-2-naphthyl sulfate can be used to probe heme accessibility in heme proteins

The phosphorescence properties of 6-bromo-2-naphthyl sulfate (BNS) in aqueous solution were studied. The phosphorescence lifetime is several hundred microseconds and is self-quenched. Although a fluorescent photoproduct is formed from BNS, it does not interfere with the decay properties of triplet-state BNS and its utility as a probe of the accessibility of the heme group in heme proteins. Quenching of BNS phosphorescence does not occur for the non-heme protein lysozyme and apomyoglobin but occurs by a dynamic mechanism with a quenching constant of 1-2 x 10(9) M-1 s-1 for cytochrome c and myoglobin and with a quenching constant of 6.2 x 10(9) M-1 s-1 for protoporphyrin IX. The phosphorescence of an inclusion complex of 1-bromonaphthalene and beta-cyclodextrin is not quenched by heme-containing proteins. The temperature and viscosity dependencies of the rate with which BNS phosphorescence is quenched by microperoxidase-11 are consistent with unit quenching efficiency. These results indicate that quenching of BNS phosphorescence occurs only upon contact with the quencher, and the quenching constant can be used to assess the degree of accessibility of the heme group.

Differential dependence of early and late increases in 1,2-diacylglycerol on the presence of catalytically active alpha-thrombin: evidence for regulation at the level of 1,2-diacylglycerol generation

alpha-Thrombin stimulates a biphasic increase in cellular 1,2-diacylglycerol mass in quiescent IIC9 fibroblasts. This report describes the use of hirudin, a high-affinity inhibitor of alpha-thrombin that renders it catalytically inactive, to investigate the dependence of elevated 1,2-diacylglycerol levels on the presence of catalytically active alpha-thrombin. When cultures were incubated in the presence of alpha-thrombin, 1,2-diacylglycerol levels remained elevated for greater than or equal to 4 h. Inactivation of alpha-thrombin after 15 s did not alter the kinetics of 1,2-diacylglycerol formation occurring over the next 1 h. However, sustained (1-4 h) increases in this lipid were eliminated. Inactivation of alpha-thrombin after 1 h of stimulation resulted in 1) an immediate and reversible decline in 1,2-diacylglycerol levels, 2) elimination of the sustained phase of 1,2-diacylglycerol production, 3) inhibition of the alpha-thrombin-stimulated generation of choline metabolites, and 4) a blunted mitogenic response to alpha-thrombin. These data indicate that early (0-1 h) and late (1-4 h) increases in 1,2-diacylglycerol are differentially dependent on the presence of catalytically active alpha-thrombin. Furthermore, sustained increases in 1,2-diacylglycerol in response to alpha-thrombin are regulated at least in part at the level of generation (via phosphatidylcholine hydrolysis). Our results also support a role for sustained 1,2-diacylglycerol levels in the mitogenic response.

Dissociation of protein kinase C activation and sn-1,2-diacylglycerol formation. Comparison of phosphatidylinositol- and phosphatidylcholine-derived diglycerides in alpha-thrombin-stimulated fibroblasts

Diacylglycerols (DAGs) derived from phosphatidylcholine (PC) hydrolysis have been shown to activate protein kinase C (PKC) in vitro, but it is not known whether this event occurs in response to DAGs generated via agonist-induced PC hydrolysis in intact cells. In this report we have addressed this question directly, using alpha-thrombin stimulation of IIC9 fibroblasts. PKC activation in intact cells was assessed in two ways, by measuring: 1) PKC membrane association as determined by kinase activity and Western blot analysis and 2) the phosphorylation of an endogenous PKC substrate, an 80-kDa protein. Treatment with 500 ng/ml alpha-thrombin has been shown to stimulate both phosphoinositide and PC hydrolysis, whereas treatment with 100 pg/ml alpha-thrombin stimulates only PC breakdown. Using these two conditions, we show that DAG produced from phosphoinositide, but not PC hydrolysis, is associated with the activation of PKC.

5' regulatory region of a novel cytokine gene mediates selective activation by interferon gamma

A newly described member of the platelet factor 4 family of cytokine genes, mig, is selectively induced by interferon gamma (IFN-gamma), and not IFN-alpha, in the mouse macrophage-like cell line RAW 264.7. Treatment of RAW 264.7 cells with IFN-gamma activated mig gene transcription as determined by nuclear run-on assays. mig genomic clones were isolated, and constructs containing genomic fragments that included the mig promoter region and the CAT reporter gene were prepared. In RAW 264.7 cells transfected with these constructs, CAT activity was found to be selectively induced by IFN-gamma. A 278-bp genomic fragment containing 235 nucleotides 5' of the transcription start site was sufficient for IFN-gamma-selective induction of CAT activity. Analysis of 5' deletion mutants localized a region essential for activation by IFN-gamma to within 64 nucleotides extending from -235 to -172. A genomic fragment containing this sequence was capable of conferring IFN-gamma inducibility to constructs with a heterologous promoter.

Kinetic and molecular species analyses of mitogen-induced increases in diglycerides: evidence for stimulated hydrolysis of phosphoinositides and phosphatidylcholine

A wide variety of agonist-induced events appear to be mediated through an increase in cellular diglyceride levels. With regard to the ability of diglycerides to mediate these events, three important parameters must be considered: a) the kinetics of diglyceride generation, b) the absolute mass levels, and c) their molecular species. While this increase is often due to a stimulated hydrolysis of phosphoinositides, there is increasing evidence that the stimulated hydrolysis of phosphatidylcholine also contributes to agonist-induced increases in diglyceride levels. The kinetics of mass increases in diglyceride levels stimulated in cultured fibroblasts are agonist-dependent. High concentrations of alpha-thrombin stimulate a biphasic increase in diglyceride levels with the first phase peaking at 15 s and the second phase peaking at 5 min. In contrast, stimulation with epidermal growth factor, or platelet-derived growth factor, results in a monophasic increase in cellular diglyceride levels. Furthermore, the molecular species and phospholipid source of the stimulated diglycerides are also agonist-dependent. While the hydrolysis of phosphoinositides is major source of diglycerides initially generated in response to some agonists (15 s with alpha-thrombin at 500 ng/ml), phosphatidylcholine is hydrolyzed as well. Following longer incubations, or at all times following stimulation by epidermal growth factor or platelet-derived growth factor, phosphatidylcholine hydrolysis is the principal source of the stimulated diglycerides.

Sustained increase in 1,2-diacylglycerol precedes DNA synthesis in epidermal-growth-factor-stimulated fibroblasts. Evidence for stimulated phosphatidylcholine hydrolysis

A property common to many growth factors is that they must be present for several hours before the commitment to DNA synthesis and cell division occurs. The intracellular signals that are relevant during this period are poorly defined. We examined the formation of 1,2-diacylglycerol in IIC9 fibroblasts after stimulation with epidermal growth factor (EGF), and found that the mass of this lipid remained elevated for at least four hours. The concentration-dependence of EGF-stimulated 1,2-diacylglycerol production and [3H]thymidine incorporation were similar. Studies of phospholipid metabolism strongly suggested that phosphatidylcholine was the source of the 1,2-diacylglycerol generated in response to EGF. EGF did not stimulate the hydrolysis of other phospholipids, including the phosphoinositides, nor did it increase synthesis de novo of 1,2-diacylglycerol. This pattern of sustained 1,2-diacylglycerol formation from phosphatidylcholine may be important in the mitogenic signalling of EGF and potentially other growth factors.

Lysophosphatidylcholine metabolism to 1,2-diacylglycerol in lymphoblasts: involvement of a phosphatidylcholine-hydrolyzing phospholipase C

We have previously described the chemoattraction of lymphoblasts by lysophosphatidylcholine [Hoffman, R. D., et al. (1982) Proc. Natl. Acad. Sci. U.S.A. 79, 3285-3289]. In studying the mechanism of chemoattraction it was found that lysophosphatidylcholine was metabolized to 1,2-diacylglycerol by the lymphoblastic cell line 6C3HED. One route of metabolism involves the acylation of lysophosphatidylcholine to phosphatidylcholine with subsequent hydrolysis to 1,2-diacylglycerol and phosphocholine by the action of phospholipase C. The increase in cellular 1,2-diacylglycerol was established by metabolic experiments using [14C]glycerol-labeled lysophosphatidylcholine and by mass measurements of 1,2-diacylglycerol. The presence of a phosphatidylcholine-hydrolyzing phospholipase C was confirmed in 6C3HED cell homogenates. In intact cells, lysophosphatidylcholine induced a pattern of protein phosphorylation similar to those of 1,2-dioctanoylglycerol and phorbol 12-myristate 13-acetate, two known activators of protein kinase C. This pathway of lysophosphatidylcholine metabolism, which involves a phosphatidylcholine-hydrolyzing phospholipase C, may be important in the activation of protein kinase C independent of inositol phospholipid hydrolysis.

Analysis of surface damage in retrieved carbon fiber-reinforced and plain polyethylene tibial components from posterior stabilized total knee replacements

The performance of carbon fiber-reinforced ultra-high molecular weight polyethylene was compared with that of plain (non-reinforced) polyethylene on the basis of the damage that was observed on the articulating surfaces of retrieved tibial components of total knee prostheses. Established microscopy techniques for subjectively grading the presence and extent of surface damage and the histological structure of the surrounding tissues were used to evaluate twenty-six carbon fiber-reinforced and twenty plain polyethylene components that had been retrieved after an average of twenty-one months of implantation. All of the tibial components were from the same design of total knee replacement. The two groups of patients from whom the components were retrieved did not differ with regard to weight, the length of time that the component had been implanted, the radiographic position and angular alignment of the component, the original diagnosis, or the reason for removal of the component. The amounts and types of damage that were observed did not differ for the two materials. For both materials, the amount of damage was directly related to the length of time that the component had been implanted. The histological appearance of tissues from the area around the component did not differ for the two materials, except for the presence of fragments of carbon fiber in many of the samples from the areas around carbon fiber-reinforced components.

Kinetic analysis of 1,2-diacylglycerol mass levels in cultured fibroblasts. Comparison of stimulation by alpha-thrombin and epidermal growth factor

We have examined the kinetics of 1,2-diacylglycerol production in quiescent IIC9 fibroblasts. alpha-Thrombin and epidermal growth factor (EGF) both stimulate an increase in the mass of cellular 1,2-diacylglycerol. The generation of 1,2-diacylglycerol is biphasic when stimulated by a high concentration of alpha-thrombin (500 ng/ml), with an early phase peaking at 15 s and a late phase peaking at 5 min. Production of 1,2-diacylglycerol is monophasic when stimulated by: (a) a low concentration of alpha-thrombin (100 pg/ml); (b) a high concentration of alpha-thrombin added to cultures which had been pretreated with chymotrypsin; or (c) EGF. In all cases the stimulation of 1,2-diacylglycerol was sustained for at least 30 min. In a previous report (Raben, D. M., Yasuda, K., and Cunningham, D. D. (1987) Biochemistry 26, 2759-2765), it was demonstrated that alpha-thrombin stimulates lipid metabolism in fibroblasts via two coupling mechanisms designated R1 and R2. We now present evidence that the early phase of alpha-thrombin-stimulated 1,2-diacylglycerol production is related to R1, which is characterized by: 1) increased release of arachidonic acid, 2) hydrolysis of polyphosphoinositides, and 3) inhibition by pretreating cultures with chymotrypsin. The late phase is related to R2 which is characterized by 1,2-diacylglycerol production in the absence of stimulated phosphoinositide hydrolysis and arachidonic acid release. In addition, EGF activates an R2-like mechanism in that it does not stimulate the release of arachidonic acid or hydrolysis of polyphosphoinositides but does stimulate a 2-fold increase in 1,2-diacylglycerol mass.

Acetabular cup wear in total hip arthroplasty

Clinical, pathologic, radiographic, and biomechanical factors of 10 severely worn retrieved Charnley acetabular cups were examined to determine whether these factors influenced cup wear. Change in cup thickness was found to be linear with time. It was found that the actual change in cup thickness was not significantly different from the radiographic change in cup thickness. No correlation was found with the other clinical or radiographic factors.

Leukocyte chemoattraction by 1,2-diacylglycerol

Previous reports have demonstrated the hydrolysis of inositol phospholipids in polymorphonuclear leukocytes (PMN) in response to chemoattractants and in lymphocytes in response to the mitogen phytohemagglutinin. We investigated the role of 1,2-diacylglycerol, one of the products of receptor-linked phosphatidylinositol hydrolysis, in mediating the migratory response of leukocytes. In an under-agarose migration system, we found 1,2-dioctanoylglycerol to be a strong chemoattractant for human PMN, 6C3HED (a mouse thymic lymphoma), and Jurkat (a human T-cell leukemia). By using a modified Boyden chamber assay, the migratory response of PMN to 1,2-dioctanoylglycerol was determined to be primarily chemotactic. Analysis of structural analogs indicated that both the position and number of acyl chains are important in determining chemoattractant activity. These studies demonstrate that exogenous 1,2-diacylglycerol can stimulate the directed migration of leukocytes. They further suggest that the formation of 1,2-diacylglycerol following receptor-mediated stimulation may represent a common step in the migratory responses of myeloid and lymphoid cells.

Role of complement C9 and calcium in the generation of arachidonic acid and its metabolites from rat polymorphonuclear leukocytes

We have previously shown that antibody-sensitized mouse peritoneal macrophages release arachidonic acid (C20:4) and its oxygenated derivatives when treated with complement, and that the major part of the release depended on the terminal complement complexes (TCC). To further delineate the process(es) responsible for this release we have extended our studies to rat peritoneal polymorphonuclear leukocytes (PMNs). Experiments were performed with antibody-sensitized rat PMNs labeled with [3H]C20:4 and carrying the TCC, C5b-7, C5b-8 or C5b-9. In contrast to the results of other studies, production of leukotriene B4 (LTB4), the major radiolabeled derivative, was strictly dependent on the presence of C9. However, low levels of C20:4 and prostaglandins (PGs) were produced prior to the C5b-9 stage. Kinetic studies demonstrated that release of LTB4 was rapid; the initial release occurred within 4-6 min and a second rise in release coincided with cell death. Virtually all the LTB4 produced was released as we found no evidence of retention of intracellular LTB4 at either the C5b-8 or C5b-9 stages. In the absence of extracellular calcium, the release of LTB4 was completely abolished and the release of C20:4 and PGs was drastically reduced. [3H]C20:4-labeled PMNs carrying C5b-9 did release substantial amounts of radiolabeled material in the presence of EGTA; however, the majority of this lipid was in the form of intact phospholipid and triglyceride. These results indicate that release of C20:4 and its oxygenated derivatives from rat PMNs is (1) dependent on the participation of C9 in the preexisting C5b-8 complex in the cell membrane, and (2) largely dependent on the presence of calcium.

The effect of conformity, thickness, and material on stresses in ultra-high molecular weight components for total joint replacement

Debris resulting from damage to the surface of polyethylene components of total joint replacements has previously been shown to contribute to long-term problems such as loosening and infection. Surface damage has been associated with fatigue processes due to stresses arising from contact between the metal and polyethylene components in these prostheses. In the present study, we used elasticity and finite-element solutions to determine these stresses for total hip replacements with head diameters of twenty-two and twenty-eight millimeters and for a condylar total knee replacement. We also examined the effect on these stresses of using carbon-fiber-reinforced polyethylene instead of plain polyethylene. Stresses associated with surface damage in the tibial component of the total knee replacement were much larger than those in the hip replacements. The analysis of contact stress as a function of thickness of the polyethylene insert for tibial components showed that a thickness of more than eight to ten millimeters should be maintained when possible. The contact stress in the tibial components was reduced most when the articulating surfaces were more conforming in the medial-lateral direction. Contact stresses were much less sensitive to changes in geometry in the anterior-posterior direction. For the hip components, the stresses were lower in the acetabular component of the twenty-eight-millimeter hip replacement than in the twenty-two-millimeter replacement. The use of carbon-fiber-reinforced polyethylene resulted in stresses that were higher by as much as 40 per cent. Because the contact area between articulating surfaces moves during flexion, portions of the surface will be subjected to cyclic stresses. The contact area for the knee replacements in flexion was smaller than for the hip replacements, and the range of the maximum principal stress was larger. Consequently, the combination of the higher stress and the moving contact area is more likely to cause surface damage due to fatigue in tibial components than in acetabular components, which is consistent with clinical observations.

Retrieval analysis of porous-coated components for total knee arthroplasty. A report of two cases

Retrieval analysis of two total knee replacements incorporating porous-coated components for biologic fixation was performed. The significant finding in a 63-year-old woman was fracture of the porous-coated metal backing of the tibial component, secondary to aseptic loosening. The significant findings at the time of revision surgery in an 82-year-old woman were nonuniform bone ingrowth (primarily around fixation pegs) and fracture of metal beads from the metal backing of the patellar component.

The problem of surface damage in polyethylene total knee components

Observations of surface damage on retrieved total knee polyethylene components have been combined with experimental and analytical studies of the contact problem to identify important clinical and design factors. The amount and severity of damage occurring on the articulating surfaces of knee components increases significantly with patient weight and with the length of time the component is implanted. The design variables that affect the amount of damage are component thickness, the conformity of the articulating surfaces, and the type of polyethylene material used. Surface damage will be more severe in thin (less than 4-6 mm) components and in components with relatively flat tibial articulating surfaces. Surface damage is also expected to be more extreme for carbon-reinforced polyethylene components than for components made from plain polyethylene.

The effect of centrifugation on the fracture properties of acrylic bone cements

In this study, centrifugation did not alter the static or cyclic fracture properties of bone cement. Tests of fracture toughness and fatigue-crack propagation of centrifuged specimens of commercial cements (with and without antibiotic additions) demonstrated no significant difference from control values. Among the cements tested, Palacos (with and without antibiotic) was found to have a significantly higher fracture toughness than either Simplex or Zimmer. We attributed this difference in fracture toughness to the higher molecular weight measured for the Palacos cements. For the tested cements, only Simplex had a significantly greater volume contraction on setting due to centrifugation. The results of our study demonstrate that centrifugation of bone cement does not improve the cement's resistance to fracture in the presence of surface imperfections, such as those found at the bone-cement interface.

The effect of antibiotic additions on the fracture properties of bone cements

Two commercially developed cements (Palacos and Zimmer) were tested for fracture toughness with and without gentamicin additions. Compact tension specimens were molded under standardized conditions and divided into four groups. Each group contained specimens of both plain and both antibiotic cements. One group was tested as zero-time controls. The remaining three groups were radiation sterilized. One group was tested as zero-time sterilization controls. Another group was tested after 2 months immersion in Ringer's lactate to elute gentamicin. The last group was tested after being implanted for 2 months subcutaneously in dogs. Comparison of the fracture toughness of the two zero-time groups showed no effect of radiation sterilization on any of the four types of cement. The results from both the group immersed in Ringer's solution and the group implanted in dogs showed no significant effect on fracture toughness with gentamicin additions. Both these groups, however, did have greater toughness values than the zero-time groups, probably caused by the more complete polymerization with time. Furthermore, the Palacos cement exhibited a greater toughness than the Zimmer cement. The results of this study demonstrate that the addition of gentamicin to bone cement is not deleterious to the fracture properties.

Fatigue crack propagation behavior of ultrahigh molecular weight polyethylene

The relative fatigue crack propagation resistance of plain and carbon fiber-reinforced ultrahigh molecular weight polyethylene (UHMWPE) was determined from cyclic loading tests performed on compact tension specimens machined from the tibial components of total knee prostheses. Both materials were characterized by dynamic mechanical spectroscopy, X-ray diffraction, and differential scanning calorimetry. The cyclic tests used loading in laboratory air at 5 Hz using a sinusoidal wave form. Dynamic mechanical spectroscopy showed that the reinforced UHMWPE had a higher elastic storage modulus than the plain UHMWPE, whereas X-ray diffraction and differential scanning calorimetry showed that the percent crystallinity and degree of order in the crystalline regions were similar for the two materials. Fatigue crack propagation in both materials proved to be very sensitive to small changes in the applied cyclic stress intensity range. A 10% increase in stress intensity resulted in approximately an order of magnitude increase in fatigue crack growth rate. The fatigue crack propagation resistance of the reinforced UHMWPE was found to be significantly worse than that of the plain UHMWPE. This result was attributed to poor bonding between the carbon fibers and the UHMWPE matrix and the ductile nature of the matrix itself.

Retrieval analysis of total knee prostheses: a method and its application to 48 total condylar prostheses

A technique for the classification and quantification of damage in retrieved total knee prostheses is presented and applied to the examination of 48 removed total condylar-type knee replacements. The technique involves inspection of all metallic and polyethylene components for evidence of gross deformation, fracture, and damage to articulating surfaces. A grading system was developed to quantitate surface damage on polyethylene components. Results of the examinations are combined with patient variables (weight, activity level, radiographic findings, time of implantation, and results of histology performed on surrounding tissue) to determine correlations between clinical variables and the mechanical damage experienced by the prostheses. For the 48 total condylar-type prostheses, significant positive correlations were found for the surface damage correlated with the patient's weight and the time the prosthesis was implanted.

Soft tissue attenuation of acoustic emission pulses

The soft tissue attenuation of acoustic emission signals was measured by transmitting pulses through volunteers and measuring the decay of the waveform characteristics of the pulse as a function of the thickness of the interposed tissue. Waveform characteristics of the received signal (signal duration, number of counts, peak amplitude, energy, and rise time) demonstrated an exponential decrease with increasing tissue thickness. The decrease appeared insensitive to the frequency of the pulse within the range of 50 to 600 KHz.

The effect of carbon fiber reinforcement on contact area, contact pressure, and time-dependent deformation in polyethylene tibial components

To study the mechanical behavior of a commercially available UHMWPE reinforced with carbon fibers, measurements of contact area, contact pressure and time-dependent deformation were made on tibial components from a contemporary total knee replacement loaded to physiological levels. For comparison, similar measurements were performed on identical components manufactured from plain UHMWPE. Contact area and pressure results reflected the increased stiffness of the carbon-UHMWPE material, with smaller contact areas and generally higher contact pressures versus the plain UHMWPE at the same load. Stresses in both materials under the contact area approached or exceeded the yield stresses for the materials when the physiological load was high or the radius of the femoral component indenter decreased (similar to flexion of the knee). Time-dependent deformation over a 24 h period was reduced significantly in the carbon-UHMWPE components for a high physiological load.

Mechanical properties of poly(methyl methacrylate) bone cements

Samples of low viscosity poly(methyl methacrylate) (PMMA), graphite reinforced PMMA, and graphite reinforced low viscosity PMMA were evaluated for their compression strength and fracture toughness. These results were compared with two currently used plain PMMA bone cements. There were no statistically significant differences in compression strength between the five cements. Graphite reinforcement of plain cement produced a 32% increase in fracture toughness over plain cement. Graphite reinforcement of low viscosity cement also produced a significant increase in toughness (31%) over low viscosity cement with fiber reinforcement. However, low viscosity cement demonstrated significantly less fracture toughness than plain PMMA.

Biomechanical analysis of the sliding characteristics of compression hip screws

We examined the effect of screw-plate angle on the sliding characteristics and jamming potential of four popularly used stainless-steel and cobalt-chromium-molybdenum compression hip screws. The actual coefficient of sliding friction for these alloys was measured in each device. The force on the screw required to overcome the static frictional force also was determined, by varying the lengths of screw engaged in the barrel under conditions of static equilibrium representing 130-degree and 150-degree screw-plate angles. For the 130-degree loading configuration, this force was significantly (p < 0.001) higher than that required for the 150-degree loading configuration for all four screw types. The actual coefficient of friction was relatively constant for each material, although slight variations due to differences in design between screw types were found. A positive correlation (p < 0.01) was seen between the apparent coefficient of friction (the ratio of sliding force to normal force) and the length of the screw extending from the barrel. All stainless-steel screws jammed in the 130-degree tests when not completely engaged in the barrel. None of the 150-degree tests produced jamming and none of the cobalt-chromium-molybdenum screws jammed in either the 130-degree or the 150-degree test. Examination of jammed devices by scanning electron microscopy showed galling on the superior surface of both the screw and the barrel.

CLINICAL RELEVANCE

Understanding the conditions that facilitate sliding of hip screws aids in ensuring their proper use. The higher the nail-plate angle, the easier it is to impact the hip-fixation device and thus allow bone impaction and stability at the fracture site. The potential for jamming a sliding hip screw is decreased by maximum engagement of the screw in the barrel. Differences in the material and design of sliding hip-fixation devices have relatively little effect on the sliding characteristics compared with the nail-plate angle and the engagement of the screw in the barrel.

A method for the postmortem evaluation of an in situ total hip replacement

A method was developed for the post-mortem evaluation of a total hip replacement retrieved in situ. The hip replacement had been implanted for six years. The evaluation procedure employed existing techniques in a logical sequence such that earlier tests would not compromise results from subsequent ones. These techniques included the measurement of range of motion, aspiration of the joint for analysis of debris, radionuclide arthrograms for determination of looseness of the components, gross and histological inspection of the capsule and synovial tissue, serial sectioning of the femoral component, determination of some mechanical properties of the bone and femoral stem, and scanning electron microscopy of the articulating surfaces of the prosthetic components. Positive findings in the specimen studied were: excessive wear of the articulating surface of the acetabular component, and associated polyethylene debris in the aspirate and surrounding synovial and granulation tissue.