Influence of the method of blending an antibiotic powder with an acrylic bone cement powder on physical, mechanical, and thermal properties of the cured cement

Two variants of antibiotic powder-loaded acrylic bone cements (APLBCs) are widely used in primary total joint replacements. In the United States, the antibiotic is manually blended with the powder of the cement at the start of the procedure, while, in Europe, pre-packaged commercially-available APLBCs (in which the blending is carried out using an industrial mixer) are used. Our objective was to investigate the influence of the method of blending gentamicin sulphate with the powder of the Cemex XL formulation on a wide collection of properties of the cured cement. The blending methods used were manual mixing (the MANUAL Set), use of a small-scale, easy-to-use, commercially-available mechanical powder mixer, OmoMix 1 (the MECHANICAL Set), and use of a large-scale industrial mixer (Cemex Genta) [the INDUSTRIAL Set]. In the MECHANICAL and MANUAL Sets, the blending time was 3 min. In preparing the test specimens for each set, the blended powder used contained 4.22 wt% of the gentamicin powder. The properties determined were the strength, modulus, and work-to-fracture (all obtained under four-point bending), plane-strain fracture toughness, Weibull mean fatigue life (fatigue conditions: +/-15 MPa; 2 Hz), activation energy and frequency factor for the cement polymerization process (both determined using differential scanning calorimetry, at heating rates of 5, 10, 15, and 20 Kmin(-1)), the diffusion coefficient for the absorption of phosphate buffered saline, PBS, at 37 degrees C, and the rate of elution of the gentamicin into PBS, at 37 degrees C (E). Also determined were the particle size, particle size distribution, and morphology of the blended powders and of the gentamicin. For each of the cured cement properties (except for E), there is no statistically significant difference between the means for the 3 cements, a finding that parallels the observation that there are no significant differences in either the mean particle size or the morphology of the blended cement powders. Notwithstanding these results, it is suggested that when the powder mixture is blended in the operating room, using the OmoMix 1 is more likely to produce a more consistent and reproducible mixture than when manual mixing is used.     

Effect of test specimen cross-sectional shape on the in vitro fatigue life of acrylic bone cement

Constant-amplitude uniaxial tension-compression fatigue tests were conducted on specimens fabricated from 12 sets of acrylic bone cements, covering cement formulations with three different viscosities (so-called "high-", "medium-" and "low-viscosity" varieties), two different methods of mixing the cement constituents (so-called "hand-" and "vacuum-mixed" methods) and two test specimen shapes (rectangular-cross-sectioned or "flat" and circular-cross-sectioned or "round"). The test results-namely, the number of fatigue stress cycles, N(f)-were analyzed using the linearized transformation of the three-parameter Weibull relationship, allowing the values of the Weibull mean, N(WM), to be determined for each set. Values ranged from 14,300 to 1,284,331 for the round specimen sets and from 2898 to 72,960 for the flat specimen sets. Statistical analysis of the ln N(f) data, together with an examination of the N(WM) values, showed that, for any combination of cement formulation and mixing method, round specimens had significantly longer fatigue lives compared to flat ones. These results are explained in terms of two factors. The first is the smaller surface area of the waisted zone in the round specimens compared to that in the flat specimens (nominal value of 157mm(2) versus nominal value of 185mm(2)), leading to the possibility of fewer crack initiation sites on the round specimens compared to the flat ones. Secondly, it is postulated that the crystallinity of the round specimens was higher than that of the flat ones, a consequence of the significantly lower measured residual liquid monomer contents of the former compared to the latter (3.40+/-1.28wt%/wt compared to 3.81+/-1.48wt%/wt). The significance of the present finding is that it indicates that, for a set of bone cement formulation and experimental conditions, discriminating fatigue test results are more likely to be obtained if flat, rather than round, test specimens are used.     

Sheep models of intrauterine growth restriction: fetal adaptations and consequences

1. Intrauterine growth restriction (IUGR) has been associated with poor perinatal health outcomes. Animal models have been used to investigate why IUGR is associated with a poor prognosis. The sheep has been used extensively as an experimental model for IUGR with poor placental substrate supply to the fetus induced using a range of methods, including the surgical ablation of the majority of endometrial caruncles prior to conception, experimental induction of maternal hyperthermia, ligation of an umbilical artery or embolization of the placenta in late gestation and maternal overnutrition in the pregnant adolescent ewe. 2. Fetal adaptations to fetal hypoxia and hypoglycaemia include activation of the fetal hypothalamic-pituitary-adrenal (HPA) axis and sympathetic nervous system and an associated increase in circulating cortisol and noradrenaline concentrations. Fetal cardiovascular responses vary according to the method used to induce placental dysfunction. 3. Although an array of experimental models has been used to induce placental dysfunction at different stages of fetal development, each leads to remarkably similar fetal growth, metabolic, neuroendocrine and cardiovascular adaptations and consequences. The extent and range of the fetal physiological adaptations to chronic placental insufficiency are determined by the duration of exposure and the degree of the severity of substrate supply restriction. 4. The present review summarizes how sheep models of IUGR have provided an increased understanding of the nature of the fetal adaptations to IUGR, their longer-term physiological consequences and how to improve clinical management of IUGR in human pregnancies.     

MCMI-III as a treatment outcome measure for psychiatric inpatients

The Million Clinical Multiaxial Inventory-III (MCMI-III) recently was introduced to replace and update the MCMI-II. A sample of 97 psychiatric inpatients were administered the MCMI-III shortly following admission, and again 7–10 days later. Changes in the personality and symptom scales generally paralleled those found in previous work with the MCMI-II, although the mean retest interval was considerably shorter than in the earlier study. However, some differences between the two instruments were observed, confirming the need for ongoing cross-validation work on the MCMI-III as an instrument that is distinct from the MCMI-II. © 1997 John Wiley & Sons, Inc. J Clin Psychol 53: 825–831, 1997     

Primary central nervous system tumor treatment and survival in the United States, 2004–2015

Journal of Neuro-Oncology - Brain tumor treatment and survival information is generally limited in large-scale cancer datasets. We provide a clinical investigation of current patterns of care and...