93 research outputs found
Interaction of Infall and Winds in Young Stellar Objects
The interaction of a stellar or disk wind with a collapsing environment holds
promise for explaining a variety of outflow phenomena observed around young
stars. In this paper we present the first simulations of these interactions.
The focus here is on exploring how ram pressure balance between wind and
ambient gas and post-shock cooling affects the shape of the resulting outflows.
In our models we explore the role of ram pressure and cooling by holding the
wind speed constant and adjusting the ratio of the inflow mass flux to the wind
mass flux (Mdot_a/Mdot_w) Assuming non-spherical cloud collapse, we find that
relatively strong winds can carve out wide, conical outflow cavities and that
relatively weak winds can be strongly collimated into jet-like structures. If
the winds become weak enough, they can be cut off entirely by the infalling
environment. We identify discrepancies between results from standard snowplow
models and those presented here that have important implications for molecular
outflows. We also present mass vs. velocity curves for comparison with
observations.Comment: 35 pages, 11 figures (PNG and EPS
Experimental Spinal Fusion With Recombinant Human Bone Morphogenetic Protein-2 Without Decortication of Osseous Elements
Study Design. L4-L5 intertransverse process fusions were produced with 58 Ī¼g, 230 Ī¼g, or 920 Ī¼g of recombinant human bone morphogenetic protein-2 in 20 dogs. Eleven had traditional decortication of posterior elements before insertion of the implant. Nine were left undecorticated. All animals were evaluated 3 months after surgery.
Objectives. To determine whether decortication is a prerequisite for successful fusion in the presence of osteoinductive proteins such as bone morphogenetic protein-2.
Summary of Background Data. Recombinant osteoinductive proteins can induce de novo bone in ectopic soft-tissue sites in the absence of bone marrow elements. Traditional methods for achieving spinal fusion rely on exposure of bone marrow through decortication to facilitate osteogenesis. It is hypothesized that the presence of an implanted osteoinductive protein obviates the need for exposure and release of host inductive factors.
Methods. Recombinant human bone morphogenetic protein-2-induced intertransverse process fusions were performed with and without decortication. Fusion sites were evaluated by computed tomography imaging, high-resolution radiography, manual testing, mechanical testing, and histologic analysis.
Results. One hundred percent of decorticated spines and 89% of undecorticated spines were clinically fused by 3 months. Ninety-one percent of decorticated spines and 78% of undecorticated specimens exhibited bilateral transverse process osseous bridging. The only spines that failed to achieve solid bilateral arthrodesis were in the lowest dose group. With the higher two doses, there was histologic evidence of osseous continuity between the fusion mass and undecorticated transverse processes.
Conclusions. There were no statistical differences in clinical and radiographic fusion rates between decorticated and undecorticated sites. With higher doses of recombinant human bone morphogenetic protein-2, there was little histologic distinction between fusions in decorticated versus undecorticated spines
Effective Doses of Recombinant Human Bone Morphogenetic Protein-2 in Experimental Spinal Fusion
Study Design Nineteen dogs underwent L4-L5 intertransverse process fusions with either 58 Ī¼g, 115 Ī¼g, 230 Ī¼g, 460 Ī¼g, or 920 Ī¼g of recombinant human bone morphogenetic protein-2 carried by a polylactic acid polymer. A previous study (12 dogs) compared 2300 Ī¼g of recombinant human bone morphogenetic protein-2, autogenous iliac bone, and carrier alone in this model. All fusions subsequently were compared.
Objectives To characterize the dose-response relationship of recombinant human bone morphogenetic protein-2 in a spinal fusion model.
Summary of Background Data Recombinant osteoinductive morphogens, such as recombinant human bone morphogenetic protein-2, are effective in vertebrate diaphyseal defect and spinal fusion models. It is hypothesized that the quality of spinal fusion produced with recombinant human bone morphogenetic protein-2, above a threshold dose, does not change with increasing amounts of inductive protein.
Methods After decortication of the posterior elements, the designated implants were placed along the intertransverse process space bilaterally. The fusion sites were evaluated after 3 months by computed tomography imaging, high-resolution radiography, manual testing, mechanical testing, and histologic analysis.
Results As in the study using 2300 Ī¼g of recombinant human bone morphogenetic protein-2, implantation of 58ā920 Ī¼g of recombinant human bone morphogenetic protein-2 successfully resulted in intertransverse process fusion in the dog by 3 months. This had not occurred in animals containing autograft or carrier alone. The cross-sectional area of the fusion mass and mechanical stiffness of the L4-L5 intersegment were not dose-dependent. Histologic findings varied but were not related to rhBMP-2 dose. Inflammatory reaction to the composite implant was proportional inversely to the volume of the fusion mass.
Conclusions No mechanical, radiographic, or histologic differences in the quality of intertransverse process fusion resulted from a 40-fold variation in dose of recombinant human bone morphogenetic protein-2
Protostellar Outflow Evolution in Turbulent Environments
The link between turbulence in star formatting environments and protostellar
jets remains controversial. To explore issues of turbulence and fossil cavities
driven by young stellar outflows we present a series of numerical simulations
tracking the evolution of transient protostellar jets driven into a turbulent
medium. Our simulations show both the effect of turbulence on outflow
structures and, conversely, the effect of outflows on the ambient turbulence.
We demonstrate how turbulence will lead to strong modifications in jet
morphology. More importantly, we demonstrate that individual transient outflows
have the capacity to re-energize decaying turbulence. Our simulations support a
scenario in which the directed energy/momentum associated with cavities is
randomized as the cavities are disrupted by dynamical instabilities seeded by
the ambient turbulence. Consideration of the energy power spectra of the
simulations reveals that the disruption of the cavities powers an energy
cascade consistent with Burgers'-type turbulence and produces a driving
scale-length associated with the cavity propagation length. We conclude that
fossil cavities interacting either with a turbulent medium or with other
cavities have the capacity to sustain or create turbulent flows in star forming
environments. In the last section we contrast our work and its conclusions with
previous studies which claim that jets can not be the source of turbulence.Comment: 24 pages, submitted to the Astrophysical Journa
The interactions of winds from massive young stellar objects: X-ray emission, dynamics, and cavity evolution
2D axis-symmetric hydrodynamical simulations are presented which explore the
interaction of stellar and disk winds with surrounding infalling cloud
material. The star, and its accompanying disk, blow winds inside a cavity
cleared out by an earlier jet. The collision of the winds with their
surroundings generates shock heated plasma which reaches temperatures up to
~10^8 K. Attenuated X-ray spectra are calculated from solving the equation of
radiative transfer along lines-of-sight. This process is repeated at various
epochs throughout the simulations to examine the evolution of the intrinsic and
attenuated flux. We find that the dynamic nature of the wind-cavity interaction
fuels intrinsic variability in the observed emission on timescales of several
hundred years. This is principally due to variations in the position of the
reverse shock which is influenced by changes in the shape of the cavity wall.
The collision of the winds with the cavity wall can cause clumps of cloud
material to be stripped away. Mixing of these clumps into the winds mass-loads
the flow and enhances the X-ray emission measure. The position and shape of the
reverse shock plays a key role in determining the strength and hardness of the
X-ray emission. In some models the reverse shock is oblique to much of the
stellar and disk outflows, whereas in others it is closely normal over a wide
range of polar angles. For reasonable stellar and disk wind parameters the
integrated count rate and spatial extent of the intensity peak for X-ray
emission agree with \textit{Chandra} observations of the deeply embedded MYSOs
S106 IRS4, Mon R2 IRS3 A, and AFGL 2591.(abridged)Comment: 19 pages, 14 figures, accepted for publication in MNRA
The Zinc Finger Protein A20 Inhibits TNF-induced NF-ĪŗBādependent Gene Expression by Interfering with an RIP- or TRAF2-mediated Transactivation Signal and Directly Binds to a Novel NF-ĪŗBāinhibiting Protein ABIN
The zinc finger protein A20 is a tumor necrosis factor (TNF)ā and interleukin 1 (IL-1)-inducible protein that negatively regulates nuclear factor-kappa B (NF-ĪŗB)ādependent gene expression. However, the molecular mechanism by which A20 exerts this effect is still unclear. We show that A20 does not inhibit TNF- induced nuclear translocation and DNA binding of NF-ĪŗB, although it completely prevents the TNF- induced activation of an NF-ĪŗBādependent reporter gene, as well as TNF-induced IL-6 and granulocyte macrophageācolony stimulating factor gene expression. Moreover, NF-ĪŗB activation induced by overexpression of the TNF receptorāassociated proteins TNF receptorāassociated death domain protein (TRADD), receptor interacting protein (RIP), and TNF recep- torāassociated factor 2 (TRAF2) was also inhibited by expression of A20, whereas NF-ĪŗB activation induced by overexpression of NF-ĪŗBāinducing kinase (NIK) or the human T cell leukemia virus type 1 (HTLV-1) Tax was unaffected. These results demonstrate that A20 inhibits NF-ĪŗBādependent gene expression by interfering with a novel TNF-induced and RIP- or TRAF2-mediated pathway that is different from the NIKāIĪŗB kinase pathway and that is specifically involved in the transactivation of NF-ĪŗB. Via yeast two-hybrid screening, we found that A20 binds to a novel protein, ABIN, which mimics the NF-ĪŗB inhibiting effects of A20 upon overexpression, suggesting that the effect of A20 is mediated by its interaction with this NF-ĪŗB inhibiting protein, ABIN
Early versus Delayed Decompression for Traumatic Cervical Spinal Cord Injury: Results of the Surgical Timing in Acute Spinal Cord Injury Study (STASCIS)
BACKGROUND:There is convincing preclinical evidence that early decompression in the setting of spinal cord injury (SCI) improves neurologic outcomes. However, the effect of early surgical decompression in patients with acute SCI remains uncertain. Our objective was to evaluate the relative effectiveness of early (<24 hours after injury) versus late (ā„ 24 hours after injury) decompressive surgery after traumatic cervical SCI. METHODS:We performed a multicenter, international, prospective cohort study (Surgical Timing In Acute Spinal Cord Injury Study: STASCIS) in adults aged 16-80 with cervical SCI. Enrolment occurred between 2002 and 2009 at 6 North American centers. The primary outcome was ordinal change in ASIA Impairment Scale (AIS) grade at 6 months follow-up. Secondary outcomes included assessments of complications rates and mortality. FINDINGS:A total of 313 patients with acute cervical SCI were enrolled. Of these, 182 underwent early surgery, at a mean of 14.2(Ā± 5.4) hours, with the remaining 131 having late surgery, at a mean of 48.3(Ā± 29.3) hours. Of the 222 patients with follow-up available at 6 months post injury, 19.8% of patients undergoing early surgery showed a ā„ 2 grade improvement in AIS compared to 8.8% in the late decompression group (OR = 2.57, 95% CI:1.11,5.97). In the multivariate analysis, adjusted for preoperative neurological status and steroid administration, the odds of at least a 2 grade AIS improvement were 2.8 times higher amongst those who underwent early surgery as compared to those who underwent late surgery (OR = 2.83, 95% CI:1.10,7.28). During the 30 day post injury period, there was 1 mortality in both of the surgical groups. Complications occurred in 24.2% of early surgery patients and 30.5% of late surgery patients (p = 0.21). CONCLUSION:Decompression prior to 24 hours after SCI can be performed safely and is associated with improved neurologic outcome, defined as at least a 2 grade AIS improvement at 6 months follow-up
Total disc replacement surgery for symptomatic degenerative lumbar disc disease: a systematic review of the literature
The objective of this study is to evaluate the effectiveness and safety of total disc replacement surgery compared with spinal fusion in patients with symptomatic lumbar disc degeneration. Low back pain (LBP), a major health problem in Western countries, can be caused by a variety of pathologies, one of which is degenerative disc disease (DDD). When conservative treatment fails, surgery might be considered. For a long time, lumbar fusion has been the āgold standardā of surgical treatment for DDD. Total disc replacement (TDR) has increased in popularity as an alternative for lumbar fusion. A comprehensive systematic literature search was performed up to October 2008. Two reviewers independently checked all retrieved titles and abstracts, and relevant full text articles for inclusion. Two reviewers independently assessed the risk of bias of included studies and extracted relevant data and outcomes. Three randomized controlled trials and 16 prospective cohort studies were identified. In all three trials, the total disc replacement was compared with lumbar fusion techniques. The CharitĆ© trial (designed as a non-inferiority trail) was considered to have a low risk of bias for the 2-year follow up, but a high risk of bias for the 5-year follow up. The CharitĆ© artificial disc was non-inferior to the BAKĀ® Interbody Fusion System on a composite outcome of āclinical successā (57.1 vs. 46.5%, for the 2-year follow up; 57.8 vs. 51.2% for the 5-year follow up). There were no statistically significant differences in mean pain and physical function scores. The Prodisc artificial disc (also designed as a non-inferiority trail) was found to be statistically significant more effective when compared with the lumbar circumferential fusion on the composite outcome of āclinical successā (53.4 vs. 40.8%), but the risk of bias of this study was high. Moreover, there were no statistically significant differences in mean pain and physical function scores. The Flexicore trial, with a high risk of bias, found no clinical relevant differences on pain and physical function when compared with circumferential spinal fusion at 2-year follow up. Because these are preliminary results, in addition to the high risk of bias, no conclusions can be drawn based on this study. In general, these results suggest that no clinical relevant differences between the total disc replacement and fusion techniques. The overall success rates in both treatment groups were small. Complications related to the surgical approach ranged from 2.1 to 18.7%, prosthesis related complications from 2.0 to 39.3%, treatment related complications from 1.9 to 62.0% and general complications from 1.0 to 14.0%. Reoperation at the index level was reported in 1.0 to 28.6% of the patients. In the three trials published, overall complication rates ranged from 7.3 to 29.1% in the TDR group and from 6.3 to 50.2% in the fusion group. The overall reoperation rate at index-level ranged from 3.7 to 11.4% in the TDR group and from 5.4 to 26.1% in the fusion group. In conclusion, there is low quality evidence that the CharitĆ© is non-inferior to the BAK cage at the 2-year follow up on the primary outcome measures. For the 5-year follow up, the same conclusion is supported only by very low quality evidence. For the ProDisc, there is very low quality evidence for contradictory results on the primary outcome measures when compared with anterior lumbar circumferential fusion. High quality randomized controlled trials with relevant control group and long-term follow-up is needed to evaluate the effectiveness and safety of TDR
The efficacy of surgical decompression before 24 hours versus 24 to 72 hours in patients with spinal cord injury from T1 to L1 ā with specific consideration on ethics: a randomized controlled trial
<p>Abstract</p> <p>Background</p> <p>There is no clear evidence that early decompression following spinal cord injury (SCI) improves neurologic outcome. Such information must be obtained from randomized controlled trials (RCTs). To date no large scale RCT has been performed evaluating the timing of surgical decompression in the setting of thoracolumbar spinal cord injury. A concern for many is the ethical dilemma that a delay in surgery may adversely effect neurologic recovery although this has never been conclusively proven. The purpose of this study is to compare the efficacy of early (before 24 hours) verse late (24ā72 hours) surgical decompression in terms of neurological improvement in the setting of traumatic thoracolumbar spinal cord injury in a randomized format by independent, trained and blinded examiners.</p> <p>Methods</p> <p>In this prospective, randomized clinical trial, 328 selected spinal cord injury patients with traumatic thoracolumbar spinal cord injury are to be randomly assigned to: 1) early surgery (before 24 hours); or 2) late surgery (24ā72 hours). A rapid response team and set up is prepared to assist the early treatment for the early decompressive group. Supportive care, i.e. pressure support, immobilization, will be provided on admission to the late decompression group. Patients will be followed for at least 12 months posttrauma.</p> <p>Discussion</p> <p>This study will hopefully assist in contributing to the question of the efficacy of the timing of surgery in traumatic thoracolumbar SCI.</p> <p>Trial Registration</p> <p><b>RCT registration number: ISRCTN61263382</b></p
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