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STUDY DESIGN: The biomechanical influence of in situ setting hydroxyapatite cement was examined for use in pedicle screw revision surgery. Pull-out testing of control and pedicle screws augmented with hydroxyapatite cement was performed in human cadaver vertebrae. OBJECTIVES: To determine the immediate effect of using hydroxyapatite cement to augment revision pedicle screws after failure of the primary pedicle screw fixation. SUMMARY OF BACKGROUND DATA: The potential problems associated with using polymethylmethacrylate to augment revision pedicular instrumentation have prompted the search for other solutions. The introduction of resorbable hydroxyapatite pastes may have provided new biocompatible solutions for pedicle screw revision. METHODS: Ten human cadaver vertebrae were instrumented with 6.0-mm pedicle screws in each pedicle. The screws were loaded to failure in axial tension (pull-out). The failed pedicles then were instrumented with 7.0-mm pedicle screws, either augmented with hydroxyapatite cement or nonaugmented, which also were loaded to failure. Finally, the nonaugmented 7.0-mm screw hole was reinstrumented with a hydroxyapatite cement-augmented, 7.0-mm pedicle screw and loaded to failure. RESULTS: The pull-out strength of the 7.0-mm, hydroxyapatite cement-augmented screws was 325% (P = 2.9 x 10(-5)) of that of the 6.0-mm control screws, whereas the strength of the 7.0-mm nonaugmented screws was only 73% (P = 2.0 x 10(-2)) of that of the 6.0-mm control screws. The 7.0-mm screws augmented with hydroxyapatite cement also were able to salvage 7.0-mm pull-out sites to 384% (P = 6.9E-5) of the pull-out strength of the 7.0-mm nonaugmented screws. CONCLUSIONS: Hydroxyapatite cement may be a mechanically viable alternative to polymethyl methacrylate for augmenting revision pedicular instrumentation and should be considered for future experimental, animal, and clinical testing. 相似文献
103.
CD Carroll H Patel TO Johnson T Guo M Orlowski ZM He CL Cavallaro J Guo A Oksman IY Gluzman J Connelly D Chelsky DE Goldberg RE Dolle 《Canadian Metallurgical Quarterly》1998,8(17):2315-2320
An encoded 13,020-member combinatorial library was synthesized containing a statine core. Evaluation of this library with plasmepsin II, an aspartyl protease required for hemoglobin metabolism in the malaria parasite, led to the identification of potent and selective inhibitors as well as novel structure-activity relationships. 相似文献
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106.
The influence of hydrostatic pressure on the tensile deformation and fracture of copper 总被引:1,自引:0,他引:1
An investigation has been made into the effects of hydrostatic pressures up to 600 MPa on the tensile deformation and fracture mechanisms of commercial copper. Fracture occurred by the normal tensile fracture mechanism involving void coalescence followed by shear tearing at pressures up to 300 MPa. At pressures in excess of 300 MPa fracture occurred entirely by a mechanism involving highly localized bands of intense shear deformation. This mechanism resulted in fracture at a chisel-point so that the natural strain to fracture at these pressures approached infinity. 相似文献
107.
Just how far reactions can go after gelation during the cure of telechelic prepolymers has been a debatable point for some time. Utilizing a recently devised method,7 the curing reactions of some telechelic prepolymers were followed after the gel point. Extents of reaction above 90% occurred only in systems of average functionality close to two, functionality being the average number of reactive groups per molecule. Among systems of higher functionality, maximum extents of reaction of about 70% were most common. The final extent of reaction was only a few per cent above the extent of reaction at the gel point. The maximum extent of reaction varied with the concentration of reactive species and the relationship was a linear one at each functionality of the system. The data were consistent with PA2/r = {0.88/[(h ? 1)(j ? 1)]} + 0.10 where PA is the fraction of prepolymer reactive groups initially present which have reacted, r is the ratio of the initial number of crosslinking groups to prepolymer reactive groups, and h and j are weighted average functionalities of the two reactants. It is suggested that the limiting factor in defining the final extent of reaction in these systems is the accessibility of reactive groups as determined by solid geometry rather than thermodynamics or reaction kinetics. The final extent of cure is regularly dependent on functionality and one cannot regard functionality and maximum extent of reaction as independent variables. 相似文献
108.
Four cases of intrauterine fetal demise in term infants are presented. From these cases and other published reports, a sequence of fetal heart rate changes preceding intrapartum death is presented. Late or variable decelerations, if unrelieved or uncorrected, lead to baseline heart rate changes of tachycardia and loss of variability reflecting loss of fetal reserve and fetal distress. This is followed by an unstable heart rate, a sinusoidal pattern, or a rapidly changing fetal heart rate. The final event is a profound bradycardia just prior to fetal demise. 相似文献
109.
The contributions of the relative radius, relative wall thickness, incremental strain, incremental elastic modulus, and medial scleroprotein content to the static elastic properties of the rat aortic wall have been examined in three groups of rats. Controls, rats made hypertensive at four weeks of age, and rats whose blood pressure was lowered after 6 weeks hypertension, were studied. The results show evidence of adaptive changes in the aorta of hypertensive animals, and that irreversible alterations in the mechanical properties of the wall may be induced by a brief period of hypertension. A direct relationship between aortic medial scleroprotein content and the elastic properties of the wall is demonstrated. 相似文献
110.
Evidence for plasmid-associated crystal toxin production in Bacillus thuringiensis subsp. israelensis 总被引:1,自引:0,他引:1
RM Faust K Abe GA Held T Iizuka LA Bulla CL Meyers 《Canadian Metallurgical Quarterly》1983,9(1):98-103
Three crystalliferous (Cry+) strains of Bacillus thuringiensis subsp. israelensis (serotype 14) that produce parasporal protein crystals toxic to dipteran larvae and several acrystalliferous (Cry-) mutants, either induced or spontaneously derived from a single Cry+ parent, were examined for the presence of covalently closed circular (CCC) DNA in attempts to correlate toxin production with the presence of a specific plasmid. The plasmid profiles of both Cry+ and Cry- variants were analyzed by both a cleared lysate- and a modified Eckhardt lysate-electrophoresis technique. All of the Cry- mutants derived from the Cry+ parental strain had lost a 4.0- to 4.4-megadalton (Mdal) plasmid. Bioassay data confirmed loss of toxin production by the Cry- variants. All three Cry+ strains, including the parent of the Cry- strains, contained CCC plasmids DNAs of the following approximate molecular weights: 4.0 to 4.4, 5.2 to 6.0, and 11.4 to 13.0 Mdal. One Cry+ strain contained an additional CCC plasmid of 6.7 to 7.2 Mdal. The plasmid patterns for several Cry- derivatives differed in other respects from the pattern for their parent strain. The various Cry+ and Cry- strains could be distinguished either by phenotypical differences in antibiotic sensitivity, crystal production, and toxicity, or by differences in their plasmid profiles. 相似文献