Gas Accretion and Star Formation Rates

Cosmological numerical simulations of galaxy evolution show that accretion of metal-poor gas from the cosmic web drives the star formation in galaxy disks. Unfortunately, the observational support for this theoretical prediction is still indirect, and modeling and analysis are required to identify hints as actual signs of star-formation feeding from metal-poor gas accretion. Thus, a meticulous interpretation of the observations is crucial, and this observational review begins with a simple theoretical description of the physical process and the key ingredients it involves, including the properties of the accreted gas and of the star-formation that it induces. A number of observations pointing out the connection between metal-poor gas accretion and star-formation are analyzed, specifically, the short gas consumption time-scale compared to the age of the stellar populations, the fundamental metallicity relationship, the relationship between disk morphology and gas metallicity, the existence of metallicity drops in starbursts of star-forming galaxies, the so-called G dwarf problem, the existence of a minimum metallicity for the star-forming gas in the local universe, the origin of the alpha-enhanced gas forming stars in the local universe, the metallicity of the quiescent BCDs, and the direct measurements of gas accretion onto galaxies. A final section discusses intrinsic difficulties to obtain direct observational evidence, and points out alternative observational pathways to further consolidate the current ideas.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by Springe

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

Pubic root fractures are commonly misread as anterior column fractures by radiologists: Single-institution study from a level 1 trauma center

Background: We sought to determine how frequently pubic root fracture is incorrectly identified as anterior column fracture by radiologists and describe differences in characteristics and outcomes between injury patterns. Methods: We identified 155 patients who sustained pelvic or acetabular fractures at a single, level 1 trauma academic institution. Pelvis computed tomography (CT) scans were evaluated to determine whether patients sustained an anterior column fracture or pubic root fracture. Demographic and clinical factors such as mortality, ambulatory status, type of treatment (nonoperative/surgery), and mechanism of energy were assessed. Results: There were a total of 83 patients in the anterior column group and 72 patients in the pubic root cohort. Eighty-five percent of pubic root fractures were read as anterior column fractures by radiologists. A total of 77.8% of pubic root fractures had posterior ring involvement. Patients with true anterior column acetabular fracture were more likely to need surgery (63.86% vs 41.70%, P = 0.01) and be discharged to skilled nursing or inpatient rehabilitation (59.04% vs 40.27%, P = 0.02) compared to patients with pubic root fracture. Conclusion: Pubic root fractures are frequently misread as anterior column fractures in radiology reports. Correctly diagnosing pubic root fractures and differentiating them from anterior column acetabular fractures can have significant impact on patients

Octogenarian and Nonagenarians Are at a Higher Risk for Experiencing Adverse 30-Day Outcomes Following ORIF of Ankle Fractures

Introduction: Despite an increasing number of elderly individuals undergoing surgical fixation for ankle fractures, few studies have investigated peri-operative outcomes and safety of surgery in an octogenarian and nonagenarian population (age >80 years). Materials and methods: The 2012-2017 American College of Surgeons database was queried for patients undergoing open reduction internal fixation for isolated uni-malleolar, bi-malleolar and tri-malleolar ankle fractures. The study cohort was divided into 3 comparison groups (age 80). Multi-variate regression analyzes were used to compare the independent effect of varying age groups on 30-day post-operative outcomes while controlling for baseline clinical characteristics and co-morbidity burdens. Results: A total of 19,585 patients were included: 5.3% were >80 years, 18.1% were 65-79 years, and 76.6% were 80 years were at a significantly Abstract: higher risk of 30-day wound complications (OR 1.84; p = 0.019), pulmonary complications (OR 3.88; p < 0.001), renal complications (OR 1.96; p = 0.015), septic complications (OR 3.72; p = 0.002), urinary tract infections (OR 2.24; p < 0.001), bleeding requiring transfusion (OR 1.90; p = 0.025), mortality (or 7.44; p < 0.001), readmissions (OR 1.65; p = 0.004) and non-home discharge (OR 13.91; p < 0.001). Discussion: Octogenarians undergoing ankle fracture fixation are a high-risk population in need of significant pre-operative surgical and medical optimization. With the majority of patients undergoing non-elective ORIF procedures, it is critical to anticipate potential complications and incorporate experienced geriatric providers early in the surgical management of these patients. Conclusions: Octogenarians and nonagenarians are fundamentally distinct and vulnerable age groups with a high risk of complications, readmissions, mortality and non-home discharges compared to other geriatric (65-79 years) and non-geriatric (<65 years) patients. Pre-operative counseling and risk-stratification are essential in this vulnerable patient population

Factors Associated With Inability to Bear Weight Following Hip Fracture Surgery: An Analysis of the ACS-NSQIP Hip Fracture Procedure Targeted Database

Introduction: While the benefits of early mobility for prevention of complications such as pneumonia, thromboembolic events, and improved mortality have been well studied in postsurgical patients, it is unclear which patients may struggle to achieve full weight-bearing on the first postoperative day. Materials and Methods: The 2016 American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) Targeted Hip Fracture Database was queried regarding the ability to achieve weight-bearing on first postoperative day for older adults. Cases that occurred secondary to malignancy were excluded or for which weight-bearing was unachievable on the first postoperative day due to medical reasons were excluded. Results: A total of 6404 patients met inclusion and exclusion criteria for the study, with 1640 (25.6%) patients unable to bear weight on the first postoperative day. Following adjusted analysis, nonmodifiable patient factors such as dependent (partial or total) functional health status, dyspnea with moderate exertion (odds ratio [OR]: 1.31 [95% confidence interval, CI: 1.04-1.65]), ventilator dependency, and preoperative dementia on presentation to hospital were associated with lack of achievement of weight-bearing on the first postoperative day. Modifiable patient factors such as presence of systemic inflammatory response syndrome (OR: 1.35 [95% CI: 1.11-1.64]), delirium, and low preoperative hematocrit and modifiable system factors including delayed time to surgery, total postoperative time >90 minutes, and transfer from an outside emergency department were also associated with inability to achieve weight-bearing on the first postoperative day. Discussion: Medical teams can utilize the results from this study to better identify patients preoperatively who may be at risk of not achieving early mobilization and proactively employ implement strategies to encourage mobility as soon as possible for hip fracture patients