Are Greenhouse Gas Signals of Northern Hemisphere winter extra-tropical cyclone activity dependent on the identification and tracking algorithm?

For Northern Hemisphere extra-tropical cyclone activity, the dependency of a potential anthropogenic climate change signal on the identification method applied is analysed. This study investigates the impact of the used algorithm on the changing signal, not the robustness of the climate change signal itself. Using one single transient AOGCM simulation as standard input for eleven state-of-the-art identification methods, the patterns of model simulated present day climatologies are found to be close to those computed from re-analysis, independent of the method applied. Although differences in the total number of cyclones identified exist, the climate change signals (IPCC SRES A1B) in the model run considered are largely similar between methods for all cyclones. Taking into account all tracks, decreasing numbers are found in the Mediterranean, the Arctic in the Barents and Greenland Seas, the mid-latitude Pacific and North America. Changing patterns are even more similar, if only the most severe systems are considered: the methods reveal a coherent statistically significant increase in frequency over the eastern North Atlantic and North Pacific. We found that the differences between the methods considered are largely due to the different role of weaker systems in the specific methods.

Warm Conveyor Belts in the ERA-Interim Dataset (1979–2010): Part I: Climatology and Potential Vorticity Evolution

A global climatology of warm conveyor belts (WCBs) is presented for the years 1979–2010, based on trajectories calculated with Interim ECMWF Re-Analysis (ERA-Interim) data. WCB trajectories are identified as strongly ascending air parcels (600 hPa in 2 days) near extratropical cyclones. Corroborating earlier studies, WCBs are more frequent during winter than summer and they ascend preferentially in the western ocean basins between 25° and 50° latitude. Before ascending, WCB trajectories typically approach from the subtropics in summer and from more midlatitude regions in winter. Considering humidity, cloud water, and potential temperature along WCBs confirms that they experience strong condensation and integrated latent heating during the ascent (typically >20 K). Liquid and ice water contents along WCBs peak at about 700 and 550 hPa, respectively. The mean potential vorticity (PV) evolution shows typical tropospheric values near 900 hPa, followed by an increase to almost 1 potential vorticity unit (PVU) at 700 hPa, and a decrease to less than 0.5 PVU at 300 hPa. These low PV values in the upper troposphere constitute significant negative anomalies with amplitudes of 1–3 PVU, which can strongly influence the downstream flow. Considering the low-level diabatic PV production, (i) WCBs starting at low latitudes (<40°) are unlikely to attain high PV (due to weak planetary vorticity) although they exhibit the strongest latent heating, and (ii) for those ascending at higher latitudes, a strong vertical heating gradient and high absolute vorticity are both important. This study therefore provides climatological insight into the cloud diabatic formation of significant positive and negative PV anomalies in the extratropical lower and upper troposphere, respectively.

On the Co-Occurrence of Warm Conveyor Belt Outflows and PV Streamers*

The co-occurrence of warm conveyor belts (WCBs), strongly ascending moist airstreams in extratropical cyclones, and stratospheric potential vorticity (PV) streamers, indicators for breaking Rossby waves on the tropopause, is investigated for a 21-yr period in the Northern Hemisphere using Interim European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-Interim) data. WCB outflows and PV streamers are respectively identified as two- and three-dimensional objects and tracked during their life cycle. PV streamers are more frequent than WCB outflows and nearly 15% of all PV streamers co-occur with WCBs during their life cycle, whereas about 60% of all WCB outflows co-occur with PV streamers. Co-occurrences are most frequent over the North Atlantic and North Pacific in spring and winter. WCB outflows are often located upstream of the PV streamers and form earlier, indicating the importance of diabatic processes for downstream Rossby wave breaking. Less frequently, PV streamers occur first, leading to the formation of new WCBs.

Extended duration of torsional loading reduced the survival of the NP cells of the intervertebral disc

Introduction Previous studies on the influence of torsion and combined torsion-compression loading revealed a positive effect on the cell viability when a repetitive short-term torsion was applied at a physiological magnitude to intervertebral disc organ culture.1 However, after an extended period (8 hours) of combined torsion-compression loading, substantial cell death was detected in the nucleus pulposus (NP).2 In this follow-up study, we aimed to investigate the relationship, if any, between the duration of torsion applied to the intervertebral disc (IVD) and the level of NP cell viability. Materials and Methods Bovine caudal discs were harvested and cultured in a custom-built multiaxis dynamic loading bioreactor.2 Torsion (± 2 degrees) was applied to the samples at a frequency of 0.2 Hz. Torsion was applied for durations of 0, 1, 4, and 8 h/d, repeated over 7 days. After the last day of loading, disc tissue was dissected for analysis of cell viability and gene expression. Results Disc NP cell viability remained above 85% after torsional loading for 0, 1, or 4 h/d. Viability was statistical significantly reduced to below 70% when torsion was applied for 8 h/d (p = 0.03) (Table 1). The daily duration of torsional loading did not affect the AF cell viability (> 80% for all loading durations). The trend of collagen 2 gene upregulation and matrix metalloproteases 13 downregulation with an increasing duration of torsion was observed in both NP and AF (Fig. 1).Conclusion We have demonstrated that an extended duration of torsion could inhibit the survival of NP cells within the IVD in organ culture. Acknowledgments Funds from the Orthopedic Department of the Insel University Hospital of Bern and a private donation from Prof. Dr. Paul Heini, Spine Surgeon, Sonnenhof Clinic Bern were received to support this work. Disclosure of Interest None declared References References 1 Chan SC, Ferguson SJ, Wuertz K, Gantenbein-Ritter B. Biological response of the intervertebral disc to repetitive short-term cyclic torsion. Spine 2011;36(24):2021–2030 2 Chan SC, Walser J, Käppeli P, Shamsollahi MJ, Ferguson SJ, Gantenbein-Ritter B. Region specific response of intervertebral disc cells to complex dynamic loading: an organ culture study using a dynamic torsion-compression bioreactor. PLoS ONE 2013;8(8):e72489

Influence of screw augmentation in posterior dynamic and rigid stabilization systems in osteoporotic lumbar vertebrae: a biomechanical cadaveric study.

STUDY DESIGN Biomechanical cadaveric study. OBJECTIVE To determine whether augmentation positively influence screw stability or not. SUMMARY OF BACKGROUND DATA Implantation of pedicle screws is a common procedure in spine surgery to provide an anchorage of posterior internal fixation into vertebrae. Screw performance is highly correlated to bone quality. Therefore, polymeric cement is often injected through specifically designed perforated pedicle screws into osteoporotic bone to potentially enhance screw stability. METHODS Caudocephalic dynamic loading was applied as quasi-physiological alternative to classical pull-out tests on 16 screws implanted in osteoporotic lumbar vertebrae and 20 screws in nonosteoporotic specimen. Load was applied using 2 different configurations simulating standard and dynamic posterior stabilization devices. Screw performance was quantified by measurement of screwhead displacement during the loading cycles. To reduce the impact of bone quality and morphology, screw performance was compared for each vertebra and averaged afterward. RESULTS All screws (with or without cement) implanted in osteoporotic vertebrae showed lower performances than the ones implanted into nonosteoporotic specimen. Augmentation was negligible for screws implanted into nonosteoporotic specimen, whereas in osteoporotic vertebrae pedicle screw stability was significantly increased. For dynamic posterior stabilization system an increase of screwhead displacement was observed in comparison with standard fixation devices in both setups. CONCLUSION Augmentation enhances screw performance in patients with poor bone stock, whereas no difference is observed for patients without osteoporosis. Furthermore, dynamic stabilization systems have the possibility to fail when implanted in osteoporotic bone.

Five-year results of lumbar disc prostheses in the SWISSspine registry

PURPOSE The Swiss Federal Office of Public Health demanded a nationwide HTA registry for lumbar total disc arthroplasty (TDA), to decide about its reimbursement. The goal of the SWISS spine registry is to generate evidence about the safety and efficiency of lumbar TDA. METHODS Two hundred forty-eight cases treated between 3-2005 and 6-2006, who were eligible for the 5-year follow-up were included in the study. Follow-up rates for 3-6 months, 1, 2 and 5 years were 85.9, 77.0, 44.0 and 51.2 %, respectively. Outcome measures were back and leg pain, medication consumption, quality of life, intraoperative and postoperative complication and revision rates. Additionally, segmental mobility, ossification, adjacent and distant segment degeneration were analysed at the 5-year follow-up. RESULTS There was a significant, clinically relevant and lasting reduction of back (preop/postop 73/29 VAS points) and leg pain (preop/postop VAS 55/22) and a consequently decreased analgesics consumption and quality of life improvement (preop/postop 0.30/0.76 EQ-5D score points) until 5 years after surgery. The rates for intraoperative and early postoperative complications were 4.4 and 3.2 %, respectively. The overall complication rate during five postoperative years was 23.4 %, and the adjacent segment degeneration rate was 10.7 %. In 4.4 % of patients, a revision surgery was performed. Cumulative survivorship probability for a revision/re-intervention-free 5-year postoperative course was 90.4 %. At the 5-year follow-up, the average range of motion of the mobile segments (86.8 %) was 9.7°. In 43.9 % of patients, osteophytes at least potentially affecting the range of motion were seen. CONCLUSIONS Lumbar TDA appeared as efficient in long-term pain alleviation, consequent reduction of pain medication consumption and improvement of quality of life. The procedure also appeared sufficiently safe, but surgeons have to be aware of a list of potential adverse events. The outcome is stable over the 5-year postoperative period. The vast majority of treated segments remained mobile after 5 years, although almost half of patients showed osteophytes.

In vitro analysis of osteogenic inhibition in non-union spinal fusion caused by nucleus pulposus cells.

Discectomy and spinal fusion is the gold standard for spinal surgery to relieve pain. However, fusion can be hindered for yet unknown reasons that lead to non-fusions with pseudo-arthrosis. Clinical observations indicate that presence of residual intervertebral disc (IVD) tissue might hinder the ossification. We hypothesize that BMP-antagonists are constantly secreted by IVD cells and potentially prevent the ossification process. Furthermore, L51P, the engineered BMP2 variant, stimulates osseo-induction of bone marrow-derived mesenchymal stem cells (MSC) by antagonizing BMP-inhibitors. Human MSCs, primary nucleus pulposus (NPC) and annulus pulposus cells (AFC) were isolated and expanded in monolayer cultures up to passage 3. IVD cells were seeded in 1.2% alginate beads (4Mio/mL) and separated by culture inserts from MSCs. MSCs were kept in 1:control medium, 2:osteogenic medium±alginate beads, 3:osteogenic medium+NPC (±L51P) and 4:osteogenic medium+AFC (±L51P) for 21 days. Relative gene expression of bone-related genes, alkaline phosphatase assay and histological staining were performed. Osteogenesis of MSCs was hindered as shown by reduced alizarin red staining in the presence of NPC. No such inhibition was observed if co-cultured with alginate only or in the presence of AFC. The results were confirmed on the RNA and protein level. Addition of L51Pto the co- cultures, however, induced mineralization of MSCs in presence of NPC. We demonstrated that NPC secrete BMP-antagonists that prevent osteogenesis of MSCs and L51P can antagonize BMP-antagonists and induce bone formation.

Investigation of bone inhibition in non-union spinal fusion caused by intervertebral disc cells in vitro

Introduction: Discectomy and spinal fusion is the gold standard for spinal surgery to relieve pain. However, fusion can be hindered for yet unknown reasons that lead to non-fusions with pseudo-arthrose. It is hence appealing to develop biomaterials that can enhance bone formation. Clinical observations indicate that presence of residual intervertebral disc (IVD) tissue might hinder the ossification. We hypothesize that BMP-antagonists are constantly secreted by IVD cells and potentially prevent the ossification process. Furthermore, L51P, the engineered BMP2 variant, stimulates osteoinduction of bone marrow-derived mesenchymal stem cells (MSC) by antagonizing BMP-inhibitors. Methods: Human MSCs, primary nucleus pulposus (NPC) and annulus pulposus cells (AFC) were isolated and expanded in monolayer cultures up to passage 3. IVD cells were seeded in 1.2% alginate beads (4Mio/mL) and separated by culture inserts from MSCs in a co-culture set-up. MSCs were kept in 1:control medium, 2:osteogenic medium+alginate control, 3:osteogenic medium+NPC (±L51P) and 4:osteogenic medium+AFC (±L51P) for 21 days. Relative gene expression of bone-related genes, Alkaline Phosphatase (ALP) assay and histological staining were performed. Results: Osteogenesis of MSCs was hindered as shown by reduced alizarin red staining in the presence of NPC. No such inhibition was observed if co-cultured with alginate only or in the presence of AFC. The results were confirmed on the RNA and protein level. Addition of L51P to the co-cultures induced mineralization of MSCs, however a reduced ALP was observed. Conclusion: We demonstrated that NPC secrete BMP-antagonists that prevent osteogenesis of MSCs and L51P can antagonize BMP-antagonists and induce bone formation.