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The objective of this systematic review is to determine the fate of spinal implants when patients develop postoperative wound infection after posterior instrumental fusion in a degenerative spine.A systematic review of the English-language literature (published between January 2001 and July 2020) was undertaken to identify articles documenting the management strategy for surgical site infections (SSIs) after posterior lumbar spinal fusion. Studies on pedicle screw fixation after trauma, immunocompromised, metastatic spine disease, and combined anterior/posterior approach were excluded. Two independent reviewers assessed the level of evidence quality using the criteria set by the North American Spine Society, and disagreements were resolved by consensus.Of the 3071 citations identified, 49 met the criteria to undergo full-text review. Outcomes after SSIs were studied from a combined pool of 1150 patients who had undergone instrumental spinal fusion. The collected data showed that 456 patients (39.97%) had undergone spinal implant removal after SSI while 694 patients (60.03%) had their implants retained until the resolution of SSI. There was an absolute risk reduction (ARR) of 29% (-0.292) and a relative risk reduction (RRR) of 50.3% (-0.503) of implant removal if the patient underwent wound debridement following SSI. The number needed to treat (NNT) for wound debridement was calculated at 3.31 from our pooled cohort. The ARR in implant removal following vacuum-assisted closure (VAC) therapy was 16.6% and RRR was noted at 40.4%. This led to a high value of NNT at 6.0 patients. There was an ARR of 33.5% and a RRR of 70.7% was estimated in patients undergoing continuous irrigation.Our review of the literature suggests that surgeons prefer early wound debridement with or without negative pressure wound therapy under antimicrobial coverage for eradication of SSI after posterior lumbar spinal fusion. Implant removal is generally reserved for cases refractory to the other treatment modalities.

Redundant Nerve Roots (RNR) is a common radiological observation of elongated tortuous appearance of cauda equina nerve roots in sagittal MRI. It is considered a poor prognostic factor, but the associated spinal morphometry remains unfamiliar.A retrospective cohort study was conducted at the Aga Khan University Hospital, Pakistan. Patients, aged 18 or above, undergoing decompressive spinal surgery due to degenerative Lumbar Spinal Canal Stenosis (LSCS) in 2015 were included. Patients were divided in groups as per presence of RNR and assessed for spinal morphometric parameters.Fifty-two patients, aged 57.52 ± 12.08 years, were enrolled in the study. The patients in RNR group were older than those in non-RNR group (p = 0.023). RNR was significantly associated with sedimentation sign (15 vs 11; p = 0.011), as well as L2/L3 (12 vs 9; p = 0.043) and L3/L4 (18 vs 18; p = 0.034) stenosis. Ligamentum flavum hypertrophy at the most stenotic level was more common in the RNR group (20 vs 19; p = 0.006). The only quantitative parameter statistically associated with RNR was lower ligamentous interfacet distance (5.07 ± 1.95 vs 8.07 ± 4.26 mm; p = 0.010). All other parameters did not contribute to the development of RNR in LSCS patients. The multivariate model revealed significant contribution of age, male sex, ligamentous interfacet distance and disc bulge to develop RNR.Certain spinal morphometric parameters contribute towards RNR formation, which represents higher degree of spinal stenosis. These parameters, along with RNR, should be regularly reported for preoperative consideration of LSCS management.

Introduction After high dose chemotherapy (HDC) and autologous stem cell transplantation (auto-SCT), in patients with relapsed/refractory diffuse large B cell lymphoma (DLBCL) and Hodgkin lymphoma (HL), involved field radiation therapy (RT) for consolidation and residual/progressive disease (PD) eradication is a common practice. Materials and methods Retrospective single-institution cohort analysis to evaluate the impact of early RT after HDC auto-SCT. Results Between 1996 and October 2019, 153 patients (43 DLBCL, 110 HL) underwent RT after HDC auto-SCT. Males 95 (62%), females 58 (38%), median age 24 years. Indications for RT was consolidation 65%: residual disease eradication 16%: and PD eradication 19%. For DLBCL, the median overall survival (OS) for the above indications was not reached (NR):NR:2 months and the KM 5-year OS was 72.6%:64.3%:12.5% respectively (P ≤ .000). Pair-wise analysis showed that consolidation versus residual disease eradication had no difference (P = .88) but both were superior to PD disease eradication (P ≤ 000 and P = .005 respectively). For HL, indication for RT was, 54%:23%:24% respectively. The median OS was NR:NR:28.8 months and KM 5-year OS was 82.3%:78%:30% respectively (P ≤ .000). Pair-wise analysis showed that consolidation versus residual disease eradication had no difference (P = .98) but both were superior to the PD eradication group (P ≤ 000). RT was well tolerated with no significant long-term toxicity. Conclusion Post HDC auto-SCT RT was well tolerated. DLBCL and HL patients with residual disease treated with the RT had similar long-term survival as those who received RT for consolidation. RT failed to improve the poor survival in patients with post-HDC auto-SCT PD.

Stefan problems provide one of the most fundamental frameworks to capture phase change processes. The problem in cylindrical coordinates can model outward solidification, which ensures the thermal design and operation associated with phase change materials (PCMs). However, this moving boundary problem is highly nonlinear in most circumstances. Exact solutions are restricted to certain domains and boundary conditions. It is therefore vital to develop approximate analytical solutions based on physically tangible assumptions, e.g., a small Stefan number. A great amount of work has been done in one-phase Stefan problems, where the initial state is at its fusion temperature, yet very few literature has considered two-phase problems particularly in cylindrical coordinates. This paper conducts an asymptotic analysis for a two-phase Stefan problem for outward solidification in a hollow cylinder, consisting of three temporal and four spatial scales. The results are compared with the enthalpy method that simulates a mushy region between two phases by numerical iterations, rather than a sharp interface in Stefan problems. After studying both mathematical models, the role of mushy-zone thickness in the enthalpy method is also unveiled. Moreover, a wide range of geometric ratios, thermophysical properties and Stefan numbers are selected from the literature to explore their effects on the developed model with regards to interface motion and temperature profile. It can be concluded that the asymptotic solution is capable of tracking the moving interface and evaluating the transient temperature for various geometric ratios and thermophysical properties in PCMs. The accuracy of this solution is found to be affected by Stefan number only, and the computational cost is much less compared with the enthalpy method and other numerical schemes.

The interest in the underground seasonal thermal energy storage system as a renewable energy option for residential applications increases in the recent decades. The system, basically, uses the shallow ground as an energy reservoir that absorbs and release the heat in the hot and cold seasons, respectively. This paper presents, by means of a mathematical model, a novel open-loop ground thermal storage configuration using a network of bayonet tube heat exchangers. A validated two-dimensional multiphase model describing mass, momentum and conjugate heat transfer between a bayonet tube and surrounding ground have been used to study the influence of air inlet velocity and pipe length on the performance of the storage system. The results indicate that the air inlet velocity and the pipe length have proportional and inversely proportional relations with the amplitude of the air outlet temperature, respectively. These parameters, therefore, have a significant impact on the extracted or stored energy in the ground. The benefit of the open-loop storage system conducted here is to predict, prior numerical computation, the important characteristics such as heat transfer, pressure drop, and energy saving, correctly.

Ventilation is one of the key factors in controlling underground working environment by providing sufficient amount of fresh air for breathing, dispersing harmful gasses and dust and to some extent for heating/cooling. Insufficient airflow is dangerous for the working face and can lead to fatalities. Duct leakage is the most common reason for the insufficient fresh air in underground working and has been the subject of many studies in the literature. However, the main focus has been on ascertaining its impact on the ventilation requirements of the underground environment. This study aims to identify key variables associated with duct leakage that significantly impacts the power consumption levels of auxiliary fans which form an integral part of the underground ventilation system. A three-dimensional Computational Fluid Dynamics (CFD) modeling approach is undertaken in conjunction with Monte Carlo simulations and multiple regression analysis to quantify the effect of duct leakage on the fan operating point and discharge flow rate towards the working face. Various cases involving the positioning, orientation, and size of the rupture in the ventilation duct are simulated, and their respective effects on fan operating point and power levels are determined. Results indicate that the operating point of a fan for ventilation ducts is strongly correlated with the position and size of the rupture, resulting in reduced delivery of ventilation air towards the working face for different levels of fan power consumption.

In underground coal mines, uncontrolled accumulation of methane and fine coal dust often leads to serious incidents such as explosion. Therefore, methane and dust dispersion in underground mines is closely monitored and strictly regulated. Accordingly, significant efforts have been devoted to study methane and dust dispersion in underground mines. In this study, methane emission and dust concentration are numerically investigated using a computational fluid dynamics (CFD) approach. Various possible scenarios of underground mine configurations are evaluated. The results indicate that the presence of continuous miner adversely affects the air flow and leads to increased methane and dust concentrations. Nevertheless, it is found that such negative effect can be minimized or even neutralized by operating the scrubber fan in suction mode. In addition, it was found that the combination of scrubber fan in suction mode and brattice results in the best performance in terms of methane and dust removal from the mining face. Keywords: Dust, Methane, Mine ventilation, Mining machine

Energy conversion efficiency of a thermo photo voltaic (TPV) system strongly depends on the wall temperature and its uniformity. Therefore, improving heat transfer characteristics of these systems has been a focus of many recent studies. This study explores the effect of curvature on heat transfer, overall energy conversion, flame stability and emission levels for a circular micro-combustor with a sudden expansion (backward facing step). Uniformity index and figure of merit (FoM) have been defined to facilitate the analysis of computational results from a three-dimensional turbulent reaction model for curved micro-combustor. The results indicate an enhancement of 110 K in the outer wall temperature and a 7.84% maximum increase in overall energy conversion efficiency for curved channels relative to the straight channels. The flame structure in curved channels, however, is found to be more susceptible to instability such as flame flashback. The model indicates a maximum increase of about 2.5 m/s in the lower limit of the inlet mixture velocity for safe combustion operation in curved ducts.

Droplet solidification is governed by classical Stefan problems which have been commonly treated as a single-phase problem by the majority of the studies in the literature. This approach, however, is unable to capture the initial temperature and the start of freezing time correctly. The treatment of two-phase Stefan problem in spherical coordinates is limited. No known exact solution exists, albeit numerical solutions and asymptotics have proven to be useful. We present a singular perturbation solution in the limit of low Stefan number and arbitrary Biot number for the two-phase Stefan problem in a finite spherical domain. An asymptotic solution is developed for a droplet at a non-freezing initial temperature subjected to a convective boundary condition at the surface. The solution is developed for both long-time and short-time scales. The results from asymptotic expansion method are validated with the experimental results in the literature and are further verified by a numerical model of a freezing droplet using enthalpy–porosity method. The sensitivity of the asymptotic solution to the droplet initial temperature, Biot number, and Stefan number has also been studied. The results indicate that the solution from perturbation series and enthalpy–porosity method agrees to within 1%–10% for temperature profile and overall freezing times over a wide range of practical values for initial temperature, Stefan and Biot numbers for the application of spray freezing. Our perturbation series solution is also able to capture the effect of initial temperature on the overall freezing time of the droplet.

We present a novel, semi-analytical framework which accurately predicts every stage of droplet freezing. Supercooling degree of the freezing droplet is computed by coupling the 1-D transient heat conduction equation in spherical coordinates with a modified heterogeneous nucleation model. The coupling connects atomic-scale thermodynamic properties with bulk thermophysical properties and yields interesting insights into the freezing process. The study also develops a novel dendritic growth model for crystal propagation that takes into account the effects of non-linear interface kinetics and surface curvature. This non-equilibrium phase-change formulation during the recalescence stage is coupled with quasi-steady phase change approximation using perturbation series for equilibrium freezing stage to yield an accurate closed form solution of freezing dynamics. The temperature curves, nucleation rates, dendritic growth velocities and mass fraction evolution from the model are validated or verified with the available experimental or numerical data in the literature. The analytical framework developed is a reduced-order freezing model that is fast to compute and yields accurate results. The framework presented can be useful as a subgrid model for high-fidelity crystal growth and spray freezing simulations.

Background Neurorehabilitation is an important aspect of continuing care for neurosurgical patients with functional disability. In developing countries, where formal home nursing frequently is unavailable, ensuring care after discharge is a difficult task. Training attendants to provide nursing care is an alternate option. In this study, we compared the outcomes of patients nursed by family members versus those looked after by a professional nurse. Methods This was a retrospective observational study conducted at the Aga Khan University Hospital Karachi. The study consisted of 2 groups. Group 1 (consisting of patients cared for by a professional nurse) included 94 patients and group 2 (patients cared for by family members) included 102. All these patients had activity of daily living score of ≥3. Glasgow Outcomes Scale score, time to decannulation, development/worsening of bedsores, and mortality were recorded and compared between the groups at follow-up. Results The study included 196 patients. Traumatic brain injury was the most common diagnosis. Nursing requirements were similar between the 2 groups and included tracheostomy care, percutaneous endoscopic gastrostomy tube care, peripherally inserted central catheter line care, care of patients with no bone flap, and log-rolling. The outcomes of the 2 groups were comparable and included bedsore development/worsening of grade, Glasgow Outcomes Scale score at follow-up, time to decannulation, and 30-day mortality. Conclusions There was no statistically significant difference in outcomes of patients nursed by family members compared with the patients looked after by professional nurses.

Highlights • We reported a case of an aneurysm in the AICA-PICA variant which was subsequently excised. • Considerable variation exists in the anatomy of the vertebrobasilar system. • Understanding the variations and the aneurysms that may arise from them is an important aspect of neurosurgical practice., Introduction There are variations in the anatomy of the vertebrobasilar system amongst which the Anterior Inferior Cerebellar Artery-Posterior Inferior Cerebellar Artery (AICA-PICA) variant is thought to have a prevalence of 20–24% (based on retrospective studies). Despite this, aneurysms of the AICA-PICA variant are rare. We present a case of an AICA-PICA aneurysm and discuss its presentation and management, along with a review of literature. Presentation of case We describe the case of a 35 year old female who presented with signs of meningismus. On the basis of radiological imaging it was initially misdiagnosed as a thrombosed arteriovenous malformation (AVM). The patient was eventually discharged with a plan of interval imaging and interventional radiology (if required). The patient presented again with similar signs and symptoms. Re-evaluation of imaging revealed an aneurysm of the AICA-PICA variant which was managed surgically. Discussion Aneurysms of the AICA-PICA variant are rare. The radiological features and surgical management represent a unique clinical entity and are discussed below. Conclusion The prevalence of the AICA-PICA variant might be high but aneurysms in this vessel are rare. The scant knowledge available on this subject makes it a diagnostic difficulty.

Background The ideal conditioning regimen still remains a challenge in the autologous stem cell transplantation (ASCT) setting for relapsed/refractory Hodgkin Lymphoma (RR-HL). BEAM is the most popular preparative regimen but single agent high dose Melphalan (HDM) has also been used. However, the experience and data comparing BEAM vs. HDM are limited. Methods After the Institutional Review Board approval, we retrospectively evaluated the clinical course of 112 RR-HL patients, autografted from November 2008 till May 2017 in two different institutions. Twenty eight conditioned with HDM and compared in a matched paired analysis (1:3) with a cohort of 84 patients who received BEAM. The study groups had similar median age (30ys) and sex (M:F 1.7:1 vs. 1.8:1) and were matched for disease status before salvage (late relapse: 36 vs. 12, early relapse/primary refractory: 48 vs. 16 and disease status pre ASCT [complete remission (CR): 39 vs. 13 and partial remission (PR): 45 vs. 15]. BEAM regimen was given in the standard doses over 6 days, while HDM (200mg/m2) was given in a single day infusion. All patients received prophylaxis against microbial, fungal and viral infections; GCSF was routinely administered at the dose of 5mcg/kg at +1 day (BEAM group) and at +5 day (HDM group). The T-test and Kaplan-Meier method were used for the statistical analyses. Results The engraftment was successful; the median day for neutrophils >1000/mm3 was +11 for both groups while for platelets >20000/mm3 a faster recovery was noticed for HDM group: +13 vs. +22 days (p The 100 days non relapse mortality was acceptable for both groups: 2/84 (2.3%) in the BEAM group vs. 1/28 (3.5%) in the HDM group. Conclusion In this study, though retrospective, demonstrated that for RR-HL patients, the conditioning regimen consisting of HDM, offered at least comparable efficacy to the BEAM regimen. The earlier platelets recovery, and the shorter duration of chemotherapy administration (6 days for BEAM vs. 1 day for HDM), resulted in less hospitalization days, which along with the shorter period of GCSF administration post ASCT, may contribute to a better cost effectiveness for the HDM regimen. Nevertheless, prospective studies with larger series of patients and longer follow-up, including also a meticulous cost analysis, are warranted to determine the accurate role of single agent HDM as preparative regimen for ASCT in HL patients.

This paper presents a review of existing solar cooling technologies and a feasibility study of a solar absorption cooling system for a packaging facility at Tetrapak Lahore, Pakistan. The review includes brief description of existing chiller technologies and solar collectors. The case study includes analysis of the solar potential and design of the cooling system at considered site. The design calculations upon which the feasibility analysis is carried out are solar collector area and type, cooling capacity, cooling area. A comparison is made between solar cooling potential of Pakistan and existing sites all across the globe. Finally an economic analysis is carried out to demonstrate the financial viability of the new cooling system.

Energy conversion efficiency of a thermo photo voltaic (TPV) system strongly depends on the wall temperature and its uniformity. Therefore, improving heat transfer characteristics of these systems is a focus of many recent studies. Significant efforts have been devoted to investigate flame stabilization and heat transfer enhancement for straight channels; planar and circular. However, the investigation of the impact of curvature on heat transfer and flow characteristics of a reacting flow is limited, implying that more studies are required. This study explores the effect of curvature on heat transfer, pressure drop and emission levels for a circular micro-combustor with sudden expansion (backward facing step). The study uses steady state Reynolds Average Numerical Simulation (RANS) turbulence model along with a finite rate chemistry model to numerically investigate the flame structure inside a micro- combustor. The investigation observes significant enhancement in outer wall temperature and heat flux for curved ducts as compared to those for straight channels.

Background: Muir-Torre syndrome is a rare autosomal dominant genodermatosis, first described in 1967, characterized by the presence of sebaceous tumors and an internal malignancy in the absence of other predisposing factors. Objective: Our purpose was to review and update published literature on Muir-Torre syndrome. Methods: We describe a 66-year-old white man with a history of sebaceous tumors and newly diagnosed transitional cell cancer of the right ureter and adenocarcinoma of the jejunum. The literature on Muir-Torre syndrome is reviewed by means of MEDLINE search and available published reports and updated. Results: Only 205 cases of Muir-Torre syndrome with 399 internal malignancies have been reported. The common presentation is the presence of sebaceous tumors along with a low-grade visceral malignancy. Sebaceous tumors appeared before the internal malignancy in 45 cases (22%), concurrently in 12 (6%), and after the internal malignancy in 114 (56%). In 33 (16%) of 205 patients, a temporal relationship was not reported. The total number of sebaceous gland carcinomas reported is 44; 17 of 44 were neoplasms of the meibomian gland. Keratoacanthomas have been noted in 48 (23%) of 205 patients. Gastrointestinal cancers are the most common internal malignancies (61%), followed by genitourinary (22%). Conclusion: The presence of sebaceous tumors warrants a search for an internal malignancy. In patients with Muir-Torre syndrome, regular follow-up and search for new malignancy is mandatory. Evaluation and monitoring of the family members of patients are also necessary. Patients and their families should be counseled for genetic testing. Genetic analysis of the primary tumor and skin lesions should be arranged as an added research tool if possible to better understand the disease. (J Am Acad Dermatol 1999;41:681-6.)