Rotational averaging-out gravitational sedimentation of colloidal dispersions and phenomena

We report on the differences between colloidal systems left to evolve in the earth's gravitational field and the same systems for which a slow continuous rotation averaged out the effects of particle sedimentation on a distance scale small compared to the particle size. Several systems of micron-sized colloidal particles were studied: a hard sphere fluid, colloids interacting via long-range electrostatic repulsions above the freezing volume fraction, an oppositely charged colloidal system close to either gelation and/or crystallization, colloids with a competing short-range depletion attraction and a long-range electrostatic repulsion, colloidal dipolar chains, and colloidal gold platelets under conditions where they formed stacks. Important differences in the structure formation were observed between the experiments where the particles were allowed to sediment and those where sedimentation was averaged out. For instance, in the case of colloids interacting via long-range electrostatic repulsions, an unusual sequence of dilute-Fluid/dilute-Crystal/dense-Fluid/dense-Crystal phases was observed throughout the suspension under the effect of gravity, related to the volume fraction dependence of the colloidal interactions, whereas the system stayed homogeneously crystallized with rotation. For the oppositely charged colloids, a gel-like structure was found to collapse under the influence of gravity with a few crystalline layers grown on top of the sediment, whereas when the colloidal sedimentation was averaged out, the gel completely transformed into crystallites that were oriented randomly throughout the sample. Rotational averaging out gravitational sedimentation is an effective and cheap way to estimate the importance of gravity for colloidal self-assembly processes.Comment: 13 pages, 13 figure

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo

Markers of atherosclerosis in relation to presence and progression of knee osteoarthritis: a population-based cohort study

Objectives. To investigate the association between markers of atherosclerosis and the presence and progression of knee OA in a population-based cohort study. Methods. The study was performed within the framework of the prospective Rotterdam Study. Markers of atherosclerosis included coronary artery calcification (CAC) and plasma levels of CD40L, vascular cell adhesion molecule 1 (VCAM-1) and VEGF. CAC data were available for 1669 participants, and CD40L, VCAM-1 and VEGF data for 975. Radiographs of the knee were scored with the Kellgren and Lawrence score for OA at baseline and follow-up [average follow-up time 4.5 years (S.D. 0.5)]. We used multivariate logistic regression models with generalized estimated equations to calculate odds ratios (95% CIs) for the association of atherosclerosis markers with prevalence and progression of knee OA. Results. The mean age was 73.1 (S.D. 7.5) years. Within the study population, 18% had radiographic knee OA (11% of men and 23% of women). CAC and VEGF were not associated with prevalent knee OA. Only among women, CD40L [adjusted odds ratio 1.3 (1.1, 1.6)] and VCAM-1 [adjusted odds ratio 1.3 (1.1, 1.6)] were associated with prevalent knee OA. No associations with progression were found in women. In men, too few progressors were available to assess associations. Conclusion. In this population-based study, CAC and VEGF were not associated with the presence or progression of knee OA. Only among women, plasma levels of CD40L and VCAM-1 were higher in individuals with knee OA compared with those without knee OA. This might suggest an association between atherosclerosis and knee OA through low-grade systemic inflammation in women

Disability and not osteoarthritis predicts cardiovascular disease: a prospective population-based cohort study

Background Previous studies found an association between osteoarthritis (OA) and risk of cardiovascular disease (CVD) and therefore suggested intensive treatment of cardiovascular risk factors in OA patients. However, prospective population-based data is lacking. Objectives To investigate the association between OA and CVD longitudinally in a general population and examine the role of disability in this association. Methods This study was embedded in the Rotterdam Study, a prospective population-based cohort study in Rotterdam, the Netherlands that started in 1989. At baseline 4648 persons aged >= 55, free of CVD were classified into those with and those without radiographic or clinical OA. HRs adjusted for traditional cardiovascular risk factors for developing CVD (a composite of fatal and non-fatal coronary heart disease and stroke) were calculated. Results During a median follow-up of 14.4 years, 1230 cardiovascular events occurred, of which 101 were in participants with clinical OA. Presence of radiographic OA at baseline was not related to future CVD (HR 0.99, 95% CI 0.86 to 1.15), neither was presence of clinical OA (HR 1.09, 95% CI 0.88 to 1.34). However, persons with increasing disability were more likely to suffer a cardiovascular event compared with non-disabled persons (HR 1.26, 95% CI 1.12 to 1.42); this was independent of the presence of OA. Conclusions In this large population-based study, participants with OA were not at increased risk of CVD. The close relation between disability and osteoarthritis may explain previous findings. Further studies are required in order to clarify whether OA patients need more intensive treatment of their cardiovascular risk factors