Fractionation by Spatially Heterogeneous Diffusion: Experiments and the Two-Component Random Walk Model.

The fundamental question regarding the fractionation phenomenon is whether diffusion alone is responsible for it or whether an additional advection dynamic is involved. We studied the fractionation by diffusion of particles in spatially heterogeneous environments. By experimentally observing the time-sequential fractionation patterns of dye particles diffusing across a solid-solid interface of varying polyacrylamide gel densities, we found that the two-component diffusion model accurately captures the observed fractionation dynamics.

Biological invasion with a porous medium type diffusion in a heterogeneous space.

The knowledge of traveling wave solutions is the main tool in the study of wave propagation. However, in a spatially heterogeneous environment, traveling wave solutions do not exist, and a different approach is needed. In this paper, we study the generation and the propagation of hyperbolic scale singular limits of a KPP-type reaction-diffusion equation when the carrying capacity is spatially heterogeneous and the diffusion is of a porous medium equation type.

Morphological and molecular expression patterns of neural precursor cells derived from human fetal spinal cord in two-, three-dimensional, and organoid culture environments.

Recently, interest in three-dimensional (3D) cell or tissue organoids that may, in vitro, overcome not only the practical problems associated with fetal tissue transplantation, but also provide a potential source for the regeneration of injured spinal cords, has been increasing steadily. In this study, we showed that human neural precursor cells (hNPCs) derived from the fetal spinal cord could be incubated in serum free medium at two dimensional (2D), three dimensional (3D) and tissue organoid-systems. Additionally, we investigated morphological changes over time along with the expression of proteoglycans, collagen, or myelin in 2D, 3D and tissue-like organoids.

On the modelling of spatially heterogeneous nonlocal diffusion: deciding factors and preferential position of individuals.

We develop general heterogeneous nonlocal diffusion models and investigate their connection to local diffusion models by taking a singular limit of focusing kernels. We reveal the link between the two groups of diffusion equations which include both spatial heterogeneity and anisotropy. In particular, we introduce the notion of deciding factors which single out a nonlocal diffusion model and typically consist of the total jump rate and the average jump length.

Evolution of dietary diversity and a starvation driven cross-diffusion system as its singular limit.

We rigorously prove the passage from a Lotka-Volterra reaction-diffusion system towards a cross-diffusion system at the fast reaction limit. The system models a competition of two species, where one species has a more diverse diet than the other. The resulting limit gives a cross-diffusion system of a starvation driven type.

Adolescent Idiopathic Scoliosis Treated by Posterior Spinal Segmental Instrumented Fusion : When Is Fusion to L3 Stable?

Objective: The purpose of this study was to identify risk factors for distal adding on (AO) or distal junctional kyphosis (DJK) in adolescent idiopathic scoliosis (AIS) treated by posterior spinal fusion (PSF) to L3 with a minimum 2-year follow-up.

Methods: AIS patients undergoing PSF to L3 by two senior surgeons from 2000-2010 were analyzed. Distal AO and DJK were deemed poor radiographic results and defined as >3 cm of deviation from L3 to the center sacral vertical line (CSVL), or >10° angle at L3-4 on the posterior anterior- or lateral X-ray at ultimate follow-up.

The Incidence of Adding-On or Distal Junctional Kyphosis in Adolescent Idiopathic Scoliosis Treated by Anterior Spinal Fusion to L3 Was Significantly Higher Than by Posterior Spinal Fusion to L3.

Objective: To compare and identify risk factors for distal adding-on (AO) or distal junctional kyphosis (DJK) in adolescent idiopathic scoliosis (AIS) treated by anterior- (ASF) and posterior spinal fusion (PSF) to L3.

Methods: AIS patients undergoing ASF versus PSF to L3 from 2000-2010 were analyzed. Distal AO and DJK were deemed poor radiographic results.

State of the art: proximal junctional kyphosis-diagnosis, management and prevention.

Proximal junctional kyphosis (PJK) is a common problem that may occur following the surgical treatment of adult patients with spinal deformity. It is defined as the proximal junctional sagittal angle from the UIV and UVI + 2 of at least 10° AND at least 10° greater than the preop measurement. The reported incidence of radiographic PJK in the literature varies between 17 and 46%.

Pelvic parameters directly influence ideal S2 alar-iliac (S2AI) screw trajectory.

Background: The utilization of the S2 Alar-Iliac (S2AI) screw provides an optimal method of spinopelvic fixation. The free-hand placement of these screws obviates the use of intra-operative fluoroscopy and relies heavily on sacropelvic anatomy; variations of this anatomy could alter the ideal screw trajectory. The S2AI corridor is near several neurovascular structures, thus an accurate trajectory is critical.

Risk of rod fracture according to cross-link position in pedicle subtraction osteotomy (PSO): A finite element study.

Purpose: The purpose of this study is to investigate the effect of the cross-link position on the rod fracture phenomenon during pedicle subtraction osteotomy (PSO) surgery using finite element model (FEM).

Methods: A three-dimensional finite element model of a lumbar spine with sagittal imbalance was constructed using computed tomography data of a 65-year-old female patient. After simulating the standard PSO at the L4 level, we constructed four models, specifically a model without a cross-link and three models with a cross-link at three different sites.

Path to Prevention of Spinal Trauma in a Low- to Middle-income Country: A Single-center Study in Phnom Penh, Cambodia.

This study sought to characterize the epidemiology and outcomes of spinal trauma, with or without a neurologic deficit, at a major government hospital in Phnom Penh, Cambodia. Patient demographics, American Spinal Injury Association (ASIA) score on presentation, location of injury, and cause of injury from 316 patients from September 2013 through December 2016 were compiled. Outcome measures included length of hospitalization and surgical intervention.

Cross-link is a risk factor for rod fracture at pedicle subtraction osteotomy site: A finite element study.

Background: We aim to investigate using finite element model (FEM) whether the use of a cross-link is a risk factor for rod fracture at the pedicle subtraction osteotomy (PSO) site.

Methods: The geometry and dimensions of the FEM were obtained from a high-resolution computed tomography scan data of a 65 years old female patient with spinal sagittal imbalance. The intact model was modified to place PSO on the L4 spine.

Dose-Dependent Cytotoxicity of Gold Nanoparticles on Human Neural Progenitor Cells and Rat Brain.

Gold nanoparticles (GNPs) are utilized as diagnostic and therapeutic tools to detect and treat human disease. Researchers in the field of nanotoxicity are working to determine the physicochemical properties of nanoparticles that lead to toxicity in an effort to establish safe design rules. In this study, we performed the MTT and terminal transferase dUTP nick end labeling (TUNEL) assays to verify the cytotoxicity of GNPs on rat brain tissue and human neural progenitor cells (NPCs).

Predictive formula of ideal lumbar lordosis and lower lumbar lordosis determined by individual pelvic incidence in asymptomatic elderly population.

Purpose: This study aimed to obtain reference values of lumbar lordosis (LL) and lower LL (LLL) from normal asymptomatic groups, determine the relationship between them and pelvic incidence (PI), and establish the predictive formula for ideal LLL in the elderly Korean population.

Methods: Standing plain lateral radiographs of the whole spine, including the pelvis, were analyzed in asymptomatic adult male volunteers without back pain or prior surgery involving the spine or lower extremity. Volunteers with scoliosis, spondylolisthesis, segmental disk space narrowing, and/or compression fractures in the radiographs were excluded.

Evaluation of a more ventral starting point for thoracic pedicle screws: higher maximal insertional arc and more medial and safer screw angulation.

OBJECTIVETo demonstrate that a more ventral starting point for thoracic pedicle screw insertion, produced by aggressively removing the dorsal transverse process bone down to the superior articular facet (SAF), results in a larger margin for error and more medial screw angulation compared to the traditional dorsal starting point (DSP). The margin for error will be quantified by the maximal insertional arc (MIA).METHODSThe study population included 10 consecutive operative patients with adult idiopathic scoliosis who underwent primary surgery.

Predator-prey equations with constant harvesting and planting.

We propose Lotka-Volterra type predator-prey equations which include small constant terms. Depending on its sign, the constant may model various things. To see the effect of the constants clearly we drop all other functional responses except the ones in the original Lotka-Volterra equations.

Surgical and radiological outcomes after posterior vertebral column resection according to the surgeon's experience.

The purpose of this study was to estimate and analyze the radiological, surgical, and clinical results of posterior vertebral column resection (PVCR) according to the surgeon's experience. Although PVCR has been recognized as the most powerful surgical technique to correct severe spinal deformity, PVCR is a technically demanding procedure with a high complication rate. A retrospective review of the chart and radiographic data of 34 consecutive patients who received PVCR was carried out.

The posterior superior iliac spine and sacral laminar slope: key anatomical landmarks for freehand S2-alar-iliac screw placement.

Objective: The S2-alar-iliac (S2AI) screw is an increasingly popular method for spinopelvic fixation. The technique of freehand S2AI screw placement has been recently described. The purpose of this study was to demonstrate, through a CT imaging study of patients with spinal deformity, that screw trajectories based on the posterior superior iliac spine (PSIS) and sacral laminar slope result in reliable freehand S2AI trajectories that traverse safely above the sciatic notch.

Optimal Lowest Instrumented Vertebra for Thoracic Adolescent Idiopathic Scoliosis.

Study Design: Retrospective cohort chart review.

Objective: To determine the optimal lowest instrumented vertebra (LIV) following posterior segmental spinal instrumented fusion (PSSIF) of thoracic adolescent idiopathic scoliosis (AIS) with LIV at L2 or above.

Summary Of Background Data: Few studies evaluate the optimal LIV based on rotation or center sacral vertical line (CSVL).

Biomechanical characterization of three iliac screw fixation techniques: A finite element study.

We aim to characterize the biomechanical properties of a modified iliac screw fixation method compared with the classic iliac screw fixation and the S2 alar iliac screw (S2AI) fixation using a FEM. A three-dimensional, non-linear FEM of lumbosacral spine and pelvis (L1-pelvis) was modified to simulate 3 different iliac screw fixations based on posterior screw fusion. The peak von Mises stress (PVMS) values of the iliac screws in the 3 different iliac screw fixations were recorded in during flexion/extension/axial rotation/lateral bending.

Clinical and Radiological Outcomes of Posterior Vertebral Column Resection for Severe Spinal Deformities.

Objective: The aim of this study was to investigate clinical and radiological outcomes of patients who underwent posterior vertebral column resection (PVCR) by a single neurosurgeon in a single institution.

Methods: Thirty-four consecutive patients with severe spinal deformities who underwent PVCR between 2010 and 2016 were enrolled. The radiographic measurements included a kyphotic angle of PVCR levels (VCR angle), sagittal vertical axis (SVA), thoracic kyphosis, lumbar lordosis (LL), and spinopelvic parameters.