The Risk of Getting Worse: Predictors of Deterioration After Decompressive Surgery for Lumbar Spinal Stenosis: A Multicenter Observational Study

ObjectiveTo investigate the frequency and predictors of deterioration after decompressive surgery for single and 2-level lumbar spinal stenosis.MethodsProspectively collected data were retrieved from the Norwegian Registry for Spine Surgery. Clinically significant deterioration was defined as an 8-point increase in Oswestry disability index (ODI) between baseline and 12 months' follow-up.ResultsThere were 2181 patients enrolled in the study. Of 1735 patients with complete 12 months follow-up, 151 (8.7%) patients reported deterioration. The following variables were significantly associated with deterioration at 12 months' follow-up; decreasing age (odds ratio [OR] 1.02, 95% confidence interval [95% CI] 1.00–1.04, P = 0.046), tobacco smoking (OR 2.10, 95% CI 1.42–3.22, P = 0.000), American Society of Anesthesiologists grade ≥3 (OR 1.80, 95% CI 1.07–2.94, P = 0.025), decreasing preoperative ODI (OR 1.05, 95% CI 1.02–1.07, P = 0.000), previous surgery at the same level (OR 2.00, 95% CI 1.18–3.27, P = 0.009), and previous surgery at other lumbar levels (OR 2.10, 95% CI 1.19–3.53, P = 0.009).ConclusionsOverall risk of clinically significant deterioration in patient-reported pain and disability after decompressive surgery for lumbar spinal stenosis is approximately 9%. Predictors for deterioration are decreasing age, current tobacco smoking, American Society of Anesthesiologists grade ≥3, decreasing preoperative ODI, and previous surgery at same or different lumbar level. We suggest that these predictors should be emphasized and discussed with the patients before surgery

On the formation of string cavitation inside fuel injectors

The formation of vortex or ‘string’ cavitation has been visualised in the flow upstream of the injection hole inlet of an automotive-sized optical diesel fuel injector nozzle operating at pressures up to 2,000 bar. Three different nozzle geometries and three-dimensional flow simulations have been employed to describe how, for two adjacent nozzle holes, their relative positions influenced the formation and hole-to-hole interaction of the observed string cavitation vortices. Each hole was shown to contain two counter-rotating vortices: the first extending upstream on axis with the nozzle hole into the nozzle sac volume and the second forming a single ‘bridging’ string linked to the adjacent hole. Steady-state and transient fuel injection conditions were shown to produce significantly different nozzle-flow characteristics with regard to the formation and interaction of these vortices in the geometries tested, with good agreement between the experimental and simulation results being achieved. The study further confirms that the visualised vortices do not cavitate themselves but act as carriers of gas-phase components within the injector flow

Experimental Investigation of Confined Coaxial Swirl Flow

ABSTRACT Swirling flows are widely used in combustion chambers and furnaces, due to their effect on flame stabilization, mixing improvement and the reduction of pollutant emissions. In the present work, the isothermal flow field of a coaxial combustor is being studied. Particularly, the influence of the mass flow ratio between the outer (annular) flow and the inner (swirling) jet on the flow characteristics is being investigated. Swirl is produced by means of tangential injection. The swirling jet is introduced into the combustion chamber through a slightly conical nozzle, while a centrifugal fan supplies the annular flow. X-probe HWA measurements of the mean and turbulent flow field are presented for several distances downstream in the combustor. It is shown that variation of the mass flow ratio strongly affects the structure of the shear layer as well as the decay of the jet's swirl strength

Experimental and numerical determination of the mechanical response of teeth with reinforced posts

The aim of this study was to evaluate the mechanical behavior of endodontically treated teeth restored with fiber reinforced composite posts versus titanium posts, by both experimental testing and numerical simulation (finite element analysis (FEA)). Forty maxillary central incisors were endodontically treated to a size 45 file and then obturated using gutta-percha points and sealer with the lateral condensation technique. The teeth were divided into four groups of ten teeth each. All the posts were of similar dimensions. The first group was restored using carbon fiber reinforced posts (CB), the second and third groups were restored using glass fiber reinforced posts (DP and FW, respectively), and the fourth group (control group) was restored using conventional titanium posts (PP). Half of the specimens of every group were submitted to hydrothermal cycling (2000 cycles, at 5 °C and 55 °C, respectively). All specimens were loaded until failure at a 45° angle with respect to the longitudinal axis at a crosshead speed of 0.5 mm min-1. A two-dimensional finite element model was designed in order to simulate the experimentally obtained results. Mechanical testing revealed that teeth restored with titanium posts exhibited the highest fracture strength. Debonding of the core was the main failure mode observed in glass fiber posts, whereas vertical root fractures were observed in the titanium posts. FEA revealed that the maximum stresses were developed at the interface between the post, dentin and the composite core critical regions in all three cases. Hydrothermal cycling had no significant effect on the fracture behavior of fiber reinforced composite posts. © 2010 IOP Publishing Ltd