Clinical and hip simulator comparisons of ceramic-on-polyethylene and metal-on-polyethylene wear

The benefit of reduced polyethylene wear with ceramic in hip replacements does not seem to have been universally appreciated. In this current study, wear predictions from laboratory and clinical studies were compared for ceramic-on-polyethylene and cobalt chrome-on-polyethylene combinations. Many laboratory studies included water-based lubrication and linear-tracking mechanisms. Now it is appreciated that these were inappropriate methods, because of a propensity for very low or virtually no polyethylene wear against ceramics in water. Thus, water-based studies predicting a 20- to 80-fold advantage for ceramic-on-polyethylene compared with metal-on-polyethylene clearly were in error. However, serum-based simulator studies with high protein-concentrations generally have shown greater wear with alumina-on-polyethylene than with metal-on-polyethylene. Controversy still remains over the use of such nonphysiologic protein levels. The simulator studies were just beginning to explore the role of serum protein concentrations and the influence on the various wear models. Polyethylene wear with zirconia systems was particularly affected by serum protein concentrations. In one simulator study, use of proteins in the physiologic range resulted in the alumina-on-polyethylene wear rate decreasing to approximately 50% of that of metal-on-polyethylene. In the literature, many hip design and polyethylene variations were reported which confounded the wear analysis. Overall, the clinical data supported the superior performance of ceramic-on-polyethylene systems by a factor of 1.5- to fourfold. However, the amount of supporting data was not large. This summary of laboratory and clinical data indicated that ceramic-on-polyethylene hip replacement systems offered on average a 50% wear reduction from metal-on-polyethylene systems.

Metal-on-metal bearing in hip prosthesis generates 100-fold less wear debris than metal-on-polyethylene

Aseptic loosening due to osteolysis in total hip replacement has been related to wear debris released from prosthetic components. Retrospective longterm observations of patients with the metal-on-metal prosthesis has shown long-term survivorship and good mechanical performance. Thus, the new and modified metal-on-metal prosthesis has been introduced on the market. Historical clinical data from the 1st generation metal-on-metal hip prosthesis may not be relevant for the 2nd generation of metal-on-metal hip prosthesis. Therefore, preclinical testing of the prosthesis must be conducted before clinical evaluation. We assessed the tribological performance of the metal-on-metal prosthesis versus the metal-on-polyethylene prosthesis introduced on the market as Metasul and Protasul, respectively. In a 12-channel joint simulator, 6 metal-on-metal bearing and 3 metal on polyethylene prostheses were tested, with the same number of corresponding soak controls. The wear was assessed gravimetrically. The "steady-state" wear-rates from the metal-on-metal prosthesis were almost 100 times less than that from the metal-on-polyethylene prosthesis. The tribological wear performance of the metal-on-metal hip prosthetic system is promising.

Comparison of warfarin use in total knee replacement vs total hip replacement

The purpose of this retrospective study was to determine the efficacy of warfarin prophylaxis against deep vein thrombosis (DVT) in total hip arthroplasty (THA) vs total knee arthroplasty (TKA). A review of venograms in 223 patients with THA and in 189 cases of TKA was carried out. The overall DVT rate in THA was 22%. The overall DVT rate in TKA was 46%. We conclude that combined or alternate methods need to be used to decrease the rate of DVT following TKA to that of THA.

Charnley wear model for validation of hip simulators--ball diameter versus polytetrafluoroethylene and polyethylene wear

Wear rates of polytetrafluoroethylene (PTFE) and polyethylene cups were compared in 9-channel and 12-channel simulators, using serum lubrication and gravimetric techniques for wear assessment. Cobalt-chromium (CoCr) and alumina ceramic femoral heads in 22-42 mm diameter range were used to validate simulator wear rates against clinical data. This was also the first study of three femoral head sizes evaluated concurrently in a simulator (with three replicate specimens) and also the first report in which any wear experiments were repeated. Fluid absorption artefacts were within +/-1 per cent of wear magnitude for PTFE and +/-8 per cent for polyethylene and were corrected for. Wear rates were linear as a function of test duration. Precision within each set of three cups was within +/-6 per cent. The wear rates from experiments repeated over 15 months were reproducible to within +/-24 per cent. However, the magnitudes of the simulator wear rates were not clinically accurate, the PTFE wear rates (2843 mm3/10(6) cycles; 22 mm diameter) were over three times higher than in vivo, the polyethylene 30 to 50 per cent on the low side (23 mm3/10(6) cycles; 22 mm diameter). Volumetric wear rate increased with respect to size of femoral head and a linearly increasing relationship of 7 8 per cent/mm was evident with respect to femoral head diameter for both PTFE and polyethylene. These data compared well with the clinical data.

Reverse cholesterol transport in the rat following a short-term intravenous infusion of fat emulsion

The effect on cholesterol transport of an intravenous infusion of a fat emulsion (10%) Intralipid or 10% Lipovenös) in vivo was investigated in the rat. Intralipid (1.85 ml/hr/kg body weight in rts for 3 hr) caused a reduction (P < 0.05) in free cholesterol in the aorta (by 25%), in plasma high-density lipoproteins (64%) and in erythrocytes (11%) with a concomitant enrichment of liver free cholesterol (16%), suggesting an enhanced reverse cholesterol transport in this species. Lipovenös under the same conditions gave similar results. Our data support our previous in vivo study in man indicating that infusion of a fat emulsion is able even to remove cholesterol from the arterial wall and thereby possibly be considered as an antiatherosclerotic agent.

Correlations between fatty acid composition of the erythrocyte membrane and blood rheology data

The fatty acid composition of erythrocyte membrane phospholipids (phosphatidyl choline, PC, and phosphatidyl ethanolamine, PE) and erythrocyte filterability was studied in seven subjects with type II diabetics before and after change of therapy from oral hypoglycaemic agents to insulin. For comparison the same variables were also studied in 10 healthy controls. In the diabetic group the greatest changes in fatty acid composition were found before treatment in the PE fraction, corresponding to the inner part of the red cell membrane. We found increased values for 16:0 (p < 0.001), 18:1 (p < 0.01) and 20:4 (omega-6) (p < 0.05) and decreased values for 16:1 (p < 0.01) and 18:3 (omega-6) (p < 0.001), compared to values for the healthy controls. The proportion of fatty acids in the inner leaflet of the membrane did not correlate to the red cell filtrability in diabetics or healthy subjects. In the PC fraction, which corresponds to the outer leaflet of the erythrocyte membrane, we found higher values for 16:0 (NS), 18:1 (p < 0.05), 20:4 (omega-6) (NS) and 22:5 (omega-3) (p < 0.01), and lower values for 16:1 (p < 0.05) in diabetics, compared to healthy controls. In the PC fraction an increased proportion of 16:0 was inversely correlated with red cell transit time (RCTT) (p < 0.05), and increased proportions of 16:1 and 18:0 were correlated with a high RCTT (p < 0.05). Insulin treatment did not significantly change red cell deformability or the fatty acid composition of the red cell membrane. Our results also indicate that palmitic acid (16:0) may be favourable in the PC fraction and stearic acid (18:0) unfavourable with respect to the rheological properties of erythrocytes.

Hip-simulator ranking of polyethylene wear: comparisons between ceramic heads of different sizes

We carried out simulator studies on ceramic-polyethylene total-hip combinations to determine the volumetric wear-rates of 22 mm, 26 mm and 28 mm femoral-head sizes. Bovine-serum lubrication and 2 kN peak sinusoidal load-profile were used with polyethylene (UHMWPE) cups. Wear was assessed by gravimetric technique. Precision (9%) was ensured by the use of multiple specimens, multiple wear-events, and the linear-regression method of estimating the average wear trend, thereby reducing the inherent, unpredictable nature of each wear-event. Volumetric wear-rates for polyethylene averaged 23 mm3 per 10(6) cycles for the 22 mm ceramic head and up to 32 mm3 per 10(6) cycles for the 28 mm head. The difference between 22 mm and the larger head-sizes was significant. This may well be the first laboratory confirmation of Charnley's original clinical Low-Friction Arthroplasty concept with regard to wear rate. The wear penalty increased linearly at the rate of 6% to 9% per mm of diameter increase.

Ganglioside extraction from erythrocytes: a comparison study

Several methods for ganglioside extraction from erythrocytes have been compared. Our results show that ganglioside extraction is unfavourably affected by the addition of the solvents as a mixture and by the use of less polar solvents and by a lower total solvent-to-sample ratio. In accordance with our previous observation on cholesterol and phospholipids, the distribution of gangliosides could be uneven in an apparently monophasic extraction solvent mixture. The uneven distribution occurred during and also after the extraction (in filtration and centrifugation). In the recommended method using 19 volumes of methanol/chloroform (2:1) solvent in a one-step extraction, the above disadvantages in ganglioside extraction and quantification are kept under control. This method appears simple and it gives a high recovery of gangliosides.

Lipid changes in plasma and blood cells following intravenous 10% fat infusion in man

The effects of a 500 ml 4 hr infusion of 10% fat emulsion (Lipovenös) on the lipid content of plasma lipoproteins and blood cells, and on the platelet aggregation rate, were studied in ten volunteers. The infusion resulted in a significant (P < 0.05) initial increase in plasma total triglycerides (more than 5 times), phospholipids (28.7%) and free cholesterol (43.3%), but a decrease in the free cholesterol content of erythrocytes and mononuclear cells (by 4.4% and by 22.7%, respectively). Plasma cholesteryl ester was reduced by 18.2% after the infusion, most of the reduction being accounted for by the 16.5% reduction in high-density lipoproteins. Our findings suggest more than 35% of the free cholesterol accumulated in plasma to derive from peripheral tissues, in turn suggesting overall reverse cholesterol transport from peripheral tissues to plasma to be enhanced. Post-infusion platelet aggregation in response to adenosine disphophate was significantly reduced, the peak rate by 31% and 1 min. rate by 20.6% (P < 0.05 in both cases). These changes in plasma lipids found in normal volunteers suggest that a short-term intravenous infusion of 10% Lipovenös might also be beneficial in preventing atherosclerosis.

Lipid determination from monophasic solvent mixtures: influence of uneven distribution of lipids after filtration and centrifugation

Reasons for the variation in erythrocyte lipid extraction were investigated. We found that there was an uneven distribution of lipids after filtration (up to 10% accumulated in the filtrates) or centrifugation (up to 10% in the top fraction) of several apparently monophasic extraction systems. The uneven distribution was more pronounced in the systems containing relatively more water, or, generally speaking, with more nonpolar solvents. Ill-defined procedures using either filtration or centrifugation, therefore, could be the cause for variations in lipid extraction. A way to prevent the uneven distribution has been developed and is discussed.

Erythrocyte lipid extraction in alcohol-chloroform systems: a comparative study

Lipid extraction efficiency is variable when different methods are used on the same tissue. After a systematic comparison on erythrocytes, we found that this variability was due to several factors, such as the addition of alcohol and chloroform as a mixture, the use of repeated extractions or partition procedures after the extraction. Most important, however, was the uneven distribution of solvents and lipids in an apparently monophasic extraction system. This formation reduces lipid extraction and causes accumulation of lipids in the extract supernatant, which leads to an overestimation of the extracted lipid content. We recommend a one-step 18.75 volume of methanol-chloroform (1.5:1 v/v) method for lipid extraction from erythrocytes, with methanol added before chloroform. This method combines simplicity in the extraction procedure, complete extraction of cholesterol and total phospholipids, and reliability in the quantitation of the extracted lipids.

Pigment interferes with cholesterol analysis in erythrocyte lipid extracts: a procedure for removal

Removal of pigments from erythrocyte lipid extracts was achieved simply by adding isopropyl alcohol (2 ml) and silica gel H (0.05 g) to an aliquot of dried extract. This procedure is superior to other available methods because of its simplicity and high efficiency.

Adaptation of an enzymatic kit for the assay of cholesterol in tissue lipid extracts

In the assay for total cholesterol in lipid extracts by enzymatic methods, it was found necessary to redissolve the lipid prior to the reagent addition. Isopropyl alcohol was found to be best at promoting the colorimetric reaction. As little as 1.45 micrograms free cholesterol and 1.8 micrograms esterified cholesterol could be determined after 15 min incubation with the isopropyl alcohol-reagent. Using a formula for the correction of pigment absorbance, it was also possible to apply the enzymatic kit method to red blood cell lipid extracts.

Reverse cholesterol transport in the rat: influence of short-term D-myo-inositol-1,2,6 trisphosphate (PP56) infusion

D-myo-inositol-1,2,6 trisphosphate (PP56) was infused in rats for 3 hr at a rate of 30.28 microM/hr/kg body weight. The cholesterol content in plasma, erythrocytes, the aorta, and the liver was monitored before and at the end of the infusion and at 1 and 21 hr after the infusion. We found that the aortic total and free cholesterol content was reduced after the infusion and continuously until the end of the experiment (by 27% each after 21 hr P < 0.05, P < 0.01, respectively). Erythrocyte cholesterol was increased by 6.6% (P < 0.05) at the end of the infusion and 9.5% (P < 0.01) at the end of the experiment, while plasma and high-density lipoprotein cholesterol did not change significantly. Free cholesterol in the liver after infusion was decreased by 27% (P < 0.001) and cholesterol ester increased by 97% (P < 0.05) and did not return to the preinfusion level. Short-term PP56 infusion in the rat apparently influences cholesterol transport in a way which would suggest a promoted reverse cholesterol transport. Since the lipid values did not return to the preinfusion level, a long-term study is needed to elucidate in more detail the influence of PP56 on cholesterol metabolism in vivo.

One-dimensional thin-layer chromatographic separation of phospholipids and lysophospholipids from tissue lipid extracts

A modified one-dimensional thin-layer chromatographic procedure is presented for the separation from tissues of five phospholipids (phosphatidylserine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylcholine and sphingomyelin) and three lysophospholipids (lysophosphatidylserine, lysophosphatidylethanolamine and lysophosphatidylcholine). This is achieved by simple involvement of 0.4% ammonium sulphate in silica gel H and of acetone in a developing solvent as chloroform-methanol-acetic acid-acetone-water (40:25:7:4:2, v/v). The procedure is simple and the separation is reproducible. The weakness of this method is the partial degradation of phosphatidylethanolamine to lysophosphatidylethanolamine, but a method to prevent this degradation is also presented.

Mutagenesis and mapping of the gene for a sporulation-specific penicillin-binding protein in Bacillus subtilis

Penicillin-binding protein (PBP) 5* is produced by Bacillus subtilis only during sporulation and is believed to be required for synthesis of the peptidoglycan-like cortex layer of the spore. The structural gene (dacB) for PBP 5* was insertionally mutagenized by integration of a plasmid bearing an internal fragment of the gene, and the phenotype of the null mutant was characterized. The mutant had no apparent vegetative growth or germination defect, but it produced extremely heat-sensitive spores. This property is consistent with a defect in the amount or assembly of the cortex and supports the hypothesis that PBP 5* is required for synthesis of this structure. Analysis of the progeny after spontaneous excision of the integrated plasmid led to the conclusion that expression of the dacB gene was required only in the mother cell compartment during sporulation, which is also consistent with a role for PBP 5* in cortex synthesis and with its location in the outer forespore membrane. Genetic mapping located dacB midway between aroC (206 degrees) and lys (210 degrees) on the B. subtilis chromosome. This is a region where there are no other known spo, ger, or PBP genes. In related studies, we found that a null mutant of dacA, the structural gene for vegetative PBP 5, produced normal heat-resistant spores, which suggests that this PBP is not essential for cortex synthesis. In addition, a candidate for another sporulation-specific PBP was revealed on gels at approximately the same position as PBP 5*. The two PBPs could be distinguished by immunoassays.

Mapping of the gene for a major penicillin-binding protein to a genetically conserved region of the Bacillus subtilis chromosome and conservation of the protein among related species of Bacillus

Penicillin-binding protein 5 is the most abundant penicillin-binding protein in the vegetative membranes of Bacillus subtilis and accounts for 95% of the D,D-carboxypeptidase activity of the cell. The structural gene for penicillin-binding protein 5 was mapped to a genetically conserved region near guaB at 0 degrees on the B. subtilis chromosome, and immunoassays revealed that there is conservation of this major penicillin-binding protein among related species.

Occupational lead exposure and pituitary function

Twenty-five moderately exposed lead workers (mean blood-lead level 1.9 mumol/l) had lower plasma levels of follicle stimulating hormone than 25 individually matched controls without occupational lead exposure (blood-lead level 0.2 mumol/l). In addition, the ten most heavily exposed individuals had higher levels of thyroid stimulating hormone, and the 14 workers under the age of 40 had decreased plasma levels of luteinizing hormone and serum levels of cortisol, as compared to the controls. All values were within "normal" reference limits. There was no significant change of the plasma testosterone level. These data indicate a complex effect on the endocrine system by moderate lead exposure, possibly mediated by changes at the hypothalamic-pituitary level. Besides the effect on hormone levels, there was also a decrease in plasma selenium level for the lead exposed workers.

Determinants of kallikrein proteolysis of apolipoprotein B-100 in human blood plasma

The formation of apolipoprotein B-74, a fragment of apolipoprotein B-100, in blood plasma in vitro is shown to occur only at temperatures below 15 degrees C, and is promoted by exposure to glass and other surfaces known to activate factor XII. Removal of C-I esterase inhibitor from plasma permits formation of apolipoprotein B-74 at room temperature. These observations are consistent with conversion of prekallikrein to kallikrein by factor XII, and with evidence that kallikrein proteolysis in vitro is activated in the cold by alteration of its binding to C-I esterase inhibitor. Since the two proteolytic fragments of apolipoprotein B-100 produced by kallikrein digestion are identical to apolipoproteins B-74 and B-26, it is concluded that apolipoproteins B-74 and B-26 are in-vitro products produced in low density lipoproteins of normal plasma in the cold by kallikrein.

Fatty acid composition in plasma and platelet phospholipid in hypothyroid patients before and after 1-thyroxine substitution

The relative concentration of fatty acids in plasma and platelet phospholipids (phosphatidylcholine) was determined in 11 patients with overt hypothyroidism (S-TSH greater than 80 mU/l) before and after 1-thyroxine substitution therapy. During therapy, the linoleic (C18:2) acid content decreased (p less than 0.01) whereas longer and more desaturated fatty acids, including arachidonic (C20:4) acid, increased (p less than 0.01) in plasma phospholipids. Also, oleic (C18:1) acid decreased (p less than 0.01) while the major saturated fatty acids, palmitic (C16:0) and stearic (C18:0) acids, were stable. In platelet membrane phospholipids, a similar reciprocal change in the relative content of linoleic (C18:2) and arachidonic (C20:4) acids, respectively, occurred. In plasma, these changes in linoleic and arachidonic acids were found to be inversely correlated (r = 0.56, p less than 0.05). The change in the linoleic acid content in plasma was also correlated to that in platelets (r = 0.64, p less than 0.05). Thus, we have found that thyroid hormones positively influence the conversion of linoleic acid to longer and more polyunsaturated fatty acids in a way that affects fatty acid composition not only in plasma but also in platelet membrane phospholipids.