Restoration of pedicle screw fixation with an in situ setting calcium phosphate cement

STUDY DESIGN: Pedicle screws were pulled out of human cadaveric vertebrae before and after augmentation with polymethylmethacrylate or in situ-setting calcium phosphate cement. The fixation strength of screws augmented with calcium phosphate cement was compared with that of screws augmented with polymethylmethacrylate. OBJECTIVES: To determine whether a new in situ-setting calcium phosphate cement might be suitable for augmenting the fixation of pedicle screws. The principle objective was to compare the pull-out resistance of screws augmented with calcium phosphate cement with the pull-out behavior of screws augmented with polymethylmethacrylate. Polymethylmethacrylate augmentation was chosen as the standard because of its current clinical use. Five types of screws were tested to determine whether screw design had an effect on the efficacy of augmentation. SUMMARY OF BACKGROUND DATA: Although many factors affect the pull-out resistance of pedicle screws, a key determinant of their performance is the strength of their attachment to the spine. In elderly, osteopenic patients, the screw-bone interface is especially at risk for stripping during insertion or pull-out after surgery. In these patients, polymethylmethacrylate has been used to augment pedicle screw fixation, although its use is not without risk. In situ-setting calcium phosphate cements may provide an alternative to polymethylmethacrylate in this application. Like polymethylmethacrylate, calcium phosphate cements can be injected into the prepared screw hole. They have the added advantage of being resorbed and replaced during healing and normal bone remodeling. METHODS: Thirty human lower lumbar vertebrae (L3-L5) were implanted bilaterally with one of five types of pedicle screws (n = 6 for each screw type). The screws were pulled out 3.0 mm at 0.25 mm/sec with a servohydraulic materials testing machine. The 3.0-mm pull-out distance, which was slightly longer than one thread pitch, was designed to strip the screw-bone interface but to leave the pedicle otherwise intact. After the initial testing, the screws in each vertebrae were removed, and the screw tracks were filled with 2.0 cc of polymethylmethacrylate (one side) or calcium phosphate cement (contralateral side). After augmentation, the screws were reinserted, and the cements were allowed to harden for 24 hours. Postaugmentation testing followed the protocols for preaugmentation testing, and the pull-out resistance of screws augmented with calcium phosphate cement was compared with the pull-out resistance of screws augmented with polymethylmethacrylate. RESULTS: Mechanically, calcium phosphate cement compared favorably with polymethylmethacrylate for augmenting pedicle screws. Both restored the strength of the screw-bone interface: across all screw types, the average increase in pull-out strength was 147% with polymethylmethacrylate augmentation and 102% with calcium phosphate cement. There were no significant differences because of screw type with either type of augmentation. CONCLUSIONS: The in situ-setting calcium phosphate cement investigated in this study compared favorably with polymethylmethacrylate in a single-cycle, pull-out test of augmented pedicle screws in senile trabecular bone. With further evaluation, this cement may offer an alternative to polymethylmethacrylate for the enhancement of pedicle screw fixation clinically.     

The laboratory diagnosis of spring-summer infections in Yekaterinburg in the epidemic season for tick-borne encephalitis

The authors propose a comprehensive approach to laboratory diagnosis of seasonal transmissible infections, based on modern methods permitting etiological deciphering of disease. A universal diagnostic algorithm notably accelerated the laboratory diagnosis due to cutting the period between collection of material from a patient and consecutive screening for antibodies to agents of tick-borne encephalitis, Lyme disease, and California encephalitis.     

Efficacy of one dose fluoroquinolone before prostate biopsy

OBJECTIVES: To demonstrate the efficacy of a simple preparation for prostate biopsy (PBX) and to determine its potential cost savings. METHODS: One hundred fifty consecutive PBXs were performed using a Fleet enema and a single oral dose (300 mg) of ofloxacin as the pre-PBX preparation. RESULTS: Of the 150 PBXs we performed, only 1 (0.67%) patient developed a urinary tract infection. CONCLUSIONS: A simple and inexpensive pre-PBX preparation proved to be successful in preventing infectious complications and is presented as a potential model for inclusion in clinical pathways for diagnosing adenocarcinoma of the prostate.     

The controls of fat intake

OBJECTIVE: To present evidence on the control of the size of fatty meals in the context of the result of interactions of orosensory positive-feedback and postingestive negative-feedback mechanisms activated by fat stimuli in rodent models of feeding and of obesity. METHOD: We examined the effects of orosensory stimuli and postingestive stimuli in Sprague-Dawley rats, and in the genetically obese Zucker (fa/fa) rat. We used the sham feeding rat preparation to isolate the orosensory stimulating and postingestive satiating properties of oils. The negative-feedback satiating properties of fats were elicited by intestinal infusions of fats. The Zucker rat is an animal model of obesity with abnormal control of meal size and increased intake of fats. Using this model we further examined the interaction of orosensory and postingestive stimuli in the control of meal size. RESULTS: The orosensory properties of fats are sufficient to drive sham feeding and are not dependent on the postabsorptive metabolic consequences of oils in normal and Zucker rats. The satiating action of fats must act at preabsorptive sites because reduction of intake occurs before absorption of fat. The satiating potency of fats is dependent upon their specific chemical conformation and is mediated by endogenous cholecystokinin and afferent fibers of the abdominal vagus. We have found that oils produce significantly more orosensory positive feedback in obese Zucker rats than in lean rats in experimental tests of preference. This is probably the major abnormal mechanism responsible for the increased preference for fats that is characteristic of obese rats because we have not identified any significant decrease in the postingestive satiating potency of fats in obese Zucker rats. CONCLUSIONS: Fat intake is controlled by both orosensory and postingestive stimuli in normal and genetically obese rodents. In the Zucker rat the investigation of this model of genetic obesity has produced data that is congruent with the preference for high fat foods in obese people and suggests further experiments directed toward a deeper understanding of the controls of fat intake and how they are disordered.     

Digital wavelet-encoded MRI: a new wavelet-encoding methodology

A new digital wavelet-encoding method for MRI is described. The method differs from previously described wavelet-encoding approaches, because the point-spread function is made independent of the wavelet basis used. This has a significant practical advantage, because wavelet bases can now be considered that would otherwise be excluded due to the difficulty of precisely exciting wavelet-shaped RF profiles. The method has been implemented on a clinical MRI system, and human images are presented.     

An intriguing controversy over protein structural class prediction

A recent report by Bahar et al. [(1997), Proteins 29, 172-185] indicates that the coupling effects among different amino acid components as originally formulated by K. C. Chou [(1995), Proteins 21, 319-344] are important for improving the prediction of protein structural classes. These authors have further proposed a compact lattice model to illuminate the physical insight contained in the component-coupled algorithm. However, a completely opposite result was concluded by Eisenhaber et al. [(1996), Proteins 25, 169 179], using a different dataset constructed according to their definition. To address such an intriguing controversy, tests were conducted by various approaches for the datasets from an objective database, the SCOP database [Murzin et al. (1995), J. Mol. Biol. 247, 536-540]. The results obtained by both self-consistency and jackknife tests indicate that the overall rates of correct prediction by the algorithm incorporating the coupling effect among different amino acid components are significantly higher than those by the algorithms without counting such an effect. This is fully consistent with the physical reality that the folding of a protein is the result of a collective interaction among its constituent amino acid residues, and hence the coupling effects of different amino acid components must be incorporated in order to improve the prediction quality. It was found by a revisiting the calculation procedures by Eisenhaber et al. that there was a conceptual mistake in constructing the structural class datasets and a systematic mistake in applying the component-coupled algorithm. These findings are informative for understanding and utilizing the component-coupled algorithm to study the structural classes of proteins.     

Saccharide-assisted delivery of cytotoxic liposomes to human malignant cells

The overexpression of lectins by malignant cells was applied for in vitro targeting of liposomes equipped with a saccharide vector and loaded in the lipid phase with a lipid derivative of anticancer agent sarcolysine. The lectin specificity of human leukemia HL-60 and human lung adenocarcinoma ACL cells was revealed by tests with fluorescein-labeled sugar probes. With the help of fluorescent lipid dye it was shown that active saccharide ligands increased the level of the vectored liposome binding to malignant cells by 50-80% as compared to liposomes without vector or with inactive one. The degree of liposome/cell membrane fusion was monitored fluorometrically and was shown to be complete and independent of the vectors. The targeted drug-loaded liposomes had the cytotoxic activity 2-4 times higher as compared to the vector-free ones.