Computational issues in chemo-dynamical modelling of the formation and evolution of galaxies

Chemo-dynamical N-body simulations are an essential tool for understanding the formation and evolution of galaxies. As the number of observationally determined stellar abundances continues to climb, these simulations are able to provide new constraints on the early star formaton history and chemical evolution inside both the Milky Way and Local Group dwarf galaxies. Here, we aim to reproduce the low $\alpha$-element scatter observed in metal-poor stars. We first demonstrate that as stellar particles inside simulations drop below a mass threshold, increases in the resolution produce an unacceptably large scatter as one particle is no longer a good approximation of an entire stellar population. This threshold occurs at around $10^3\,\rm{M_\odot}$, a mass limit easily reached in current (and future) simulations. By simulating the Sextans and Fornax dwarf spheroidal galaxies we show that this increase in scatter at high resolutions arises from stochastic supernovae explosions. In order to reduce this scatter down to the observed value, we show the necessity of introducing a metal mixing scheme into particle-based simulations. The impact of the method used to inject the metals into the surrounding gas is also discussed. We finally summarise the best approach for accurately reproducing the scatter in simulations of both Local Group dwarf galaxies and in the Milky Way.Comment: 23 pages, 18 figures, accepted for publication in Astronomy and Astrophysic

No need for broad-spectrum empirical antibiotic coverage after surgical drainage of orthopaedic implant infections

Purpose: Empirical broad-spectrum antibiotic treatment for orthopaedic implant infections after surgical lavage is common practice while awaiting microbiological results, but lacks evidence. Methods: This was a single-centre cohort study from 1996 to 2010 with a follow-up of twoyears. Results: We retrieved 342 implant infections and followed them up for a median of 3.5years (61 recurred, 18%). Infected implants were arthroplasties (n = 186), different plates, nails or other osteosyntheses. The main pathogens were S. aureus (163, 49 methicillin-resistant) and coagulase-negative staphylococci (60, 45 methicillin-resistant). Median duration of empirical antibiotic coverage after surgical drainage was threedays before switching to targeted therapy. Vancomycin was the most frequent initial empirical agent (147), followed by intravenous co-amoxiclav (44). Most empirical antibiotic regimens (269, 79%) proved sensitive to the causative pathogen, but were too broad in 111 episodes (32%). Cephalosporins and penicillins were used only in 44 and ten cases, respectively, although they would have covered 59% of causative pathogens identified later. Multivariate Cox regression analysis showed that neither susceptible antibiotic coverage (compared to non-susceptible; hazard ratio 0.7, 95% confidence interval 0.4-1.2) nor broad-spectrum use (hazard ratio 1.1, 0.8-1.5) changed remission rates. Conclusions: Provided that surgical drainage is performed, broad-spectrum antibiotic coverage does not enhance remission of orthopaedic implant infections during the first threedays. If empirical agents are prescribed from the first day of infection, narrow-spectrum penicillins or cephalosporins can be considered to avoid unnecessary broad-spectrum antibiotic us

Evaluation et suivi radiologique de la prothèse Elite PlusTM

L'utilisation du ciment dans la prothétique de hanche est une contribution de Sir John Charnley et a permis d'améliorer la survie. Actuellement, on retrouve une survie à plus de 30 ans pour certaines PTH cimentées. D'après ses développeurs, la tige Elite+ est l'héritière améliorée de la prothèse de Charnley. Soixante-trois tiges Elite+ ont été revues de manière rétrospective sur une durée moyenne de 26 mois [2-62]. Les révisions pour descellement aseptique sont au nombre de 11/63 prothèses (17.5%) et le nombre de prothèses descellées est de 16/63. Les tiges de petites tailles (1 et 2) ont des taux de reprise beaucoup plus élevé (57.1% pour la taille 1 et 19.1% pour la taille 2). Les hommes ont eu plus de reprises (24.2%) par rapport aux femmes (10.4%). Ces résultats sont inférieurs à ceux de la littérature. Les modifications portées à un implant ne sont pas toujours une amélioration bien que le marketing réalisé pousse parfois à y faire croire

Tumeurs musculo-squelettiques diagnostiquées à tort comme lésions sportives

During our medical activity, we would necessarily be confronted with sport related complaints. Most of the diagnosed pathologies belong to the inflammation category and other traumas. However, as we will see in this review, we sometimes discover musculoskeletal tumours from different origins. One should never underestimate non-developing or slowly developing conditions among athletes, and to keep in mind a possible oncologic diagnosis. A critical assistance for diagnosis is given by the medical imagery with MRI being the leading technique. The aim is to avoid any delay in making the correct diagnosis, and therefore to avoid a more severe prognosis that would lead to a more radical surgery for either benign or malign tumours

A comparative assessment of small-head metal-on-metal and ceramic-on-polyethylene total hip replacement

Large-head metal-on-metal (MoM) total hip replacements (THR) have given rise to concern. Comparative studies of small-head MoM THRs over a longer follow-up period are lacking. Our objective was to compare the incidence of complications such as infection, dislocation, revision, adverse local tissue reactions, mortality and radiological and clinical outcomes in small-head (28 mm) MoM and ceramic-on-polyethylene (CoP) THRs up to 12 years post-operatively. A prospective cohort study included 3341 THRs in 2714 patients. The mean age was 69.1 years (range 24 to 98) and 1848 (55.3%) were performed in women, with a mean follow-up of 115 months (18 to 201). There were 883 MoM and 2458 CoP bearings. Crude incidence rates (cases/1000 person-years) were: infection 1.3 vs 0.8; dislocation 3.3 vs 3.1 and all-cause revision 4.3 vs 2.2, respectively. There was a significantly higher revision rate after ten years (adjusted hazard ratio 9.4; 95% CI 2.6 to 33.6) in the MoM group, and ten of 26 patients presented with an adverse local tissue reaction at revision. No differences in mortality, osteolysis or clinical outcome were seen. In conclusion, we found similar results for small-head MoM and CoP bearings up to ten years post-operatively, but after ten years MoM THRs had a higher risk of all-cause revision. Furthermore, the presence of an adverse response to metal debris seen in the small-head MOM group at revision is a cause for concern. Cite this article: Bone Joint J 2014; 96-B:868-75

Physical activity before and after primary total hip arthroplasty: a registry-based study

Detailed assessment of activity before and after total hip arthroplasty (THA) including a long-term followup period is lacking. Our objectives were to evaluate patient activity levels prior to disease onset, prior to THA, and at 5 and 10 years after surgery, and to determine the predictors of high activity 5 years after surgery

No need for broad-spectrum empirical antibiotic coverage after surgical drainage of orthopaedic implant infections

Empirical broad-spectrum antibiotic treatment for orthopaedic implant infections after surgical lavage is common practice while awaiting microbiological results, but lacks evidence