The Current Testing Protocols for Biomechanical Evaluation of Lumbar Spinal Implants in Laboratory Setting: A Review of the Literature

In vitro biomechanical investigations have become a routinely employed technique to explore new lumbar instrumentation. One of the most important advantages of such investigations is the low risk present when compared to clinical trials. However, the best use of any experimental data can be made when standard testing protocols are adopted by investigators, thus allowing comparisons among studies. Experimental variables, such as the length of the specimen, operative level, type of loading (e.g., dynamic versus quasistatic), magnitude, and rate of load applied, are among the most common variables controlled during spinal biomechanical testing. Although important efforts have been made to standardize these protocols, high variability can be found in the current literature. The aim of this investigation was to conduct a systematic review of the literature to identify the current trends in the protocols reported for the evaluation of new lumbar spinal implants under laboratory setting

Designs and Techniques That Improve the Pullout Strength of Pedicle Screws in Osteoporotic Vertebrae: Current Status

Osteoporosis is a medical condition affecting men and women of different age groups and populations. The compromised bone quality caused by this disease represents an important challenge when a surgical procedure (e.g., spinal fusion) is needed after failure of conservative treatments. Different pedicle screw designs and instrumentation techniques have been explored to enhance spinal device fixation in bone of compromised quality. These include alterations of screw thread design, optimization of pilot hole size for non-self-tapping screws, modification of the implant's trajectory, and bone cement augmentation. While the true benefits and limitations of any procedure may not be realized until they are observed in a clinical setting, axial pullout tests, due in large part to their reproducibility and ease of execution, are commonly used to estimate the device's effectiveness by quantifying the change in force required to remove the screw from the body. The objective of this investigation is to provide an overview of the different pedicle screw designs and the associated surgical techniques either currently utilized or proposed to improve pullout strength in osteoporotic patients. Mechanical comparisons as well as potential advantages and disadvantages of each consideration are provided herein

Biomechanical assessment of anterior plate system, bilateral pedicle screw and transdiscal screw system for high-grade spondylolisthesis: a finite element study

IntroductionLimited information regarding the biomechanical evaluation of various internal fixation techniques for high-grade L5-S1 spondylolisthesis is available. The stiffness of the operated segment and stress on the hardware can profoundly influence clinical outcomes and patient satisfaction. The objective of this study was to quantitatively investigate biomechanical profiles of various fusion methods used for high-grade spondylolisthesis by using finite element (FE) analysis.MethodsAn FE lumbar spine model of healthy spine was developed based on a patient’s CT scan. High-grade (III-IV) spondylolisthesis (SP model) was created by sliding L5 anteriorly and modifying L5-S1 facet joints. Three treatment scenarios were created by adding various implants to the model. These scenarios included L5-S1 interbody cage in combination with three different fixation methods–the anterior plate system (APS), bilateral pedicle screw system (BPSS), and transdiscal screw system (TSS). Range of motion (ROM), von Mises stress on cage, internal fixation as well as on the adjacent annuli were obtained and compared. The resistance to slippage was investigated by applying shear force on L5 vertebra and measuring its displacement regarding to S1.ResultsUnder different loading conditions all treatment scenarios showed substantial reduction of ROM in comparison with SP model. No notable differences in ROM were observed between treatment models. There was no notable difference in cage stress among models. The von Mises stress on the internal fixation in the TSS model was less than in APS and BPSS. The TSS model demonstrated superior resistance to shear load compared to APS and BPSS. No discernible difference was observed between the SP, APS, BPSS, and TSS models when compared the ROM for adjacent level L4-L5. TSS’s von Mises stress of the adjacent annulus was higher than in APS and BPSS.ConclusionsThe TSS model exhibited biomechanical superiority over the APS and BPSS models

Intratumoral Delivery of MDNA55, an Interleukin-4 Receptor Targeted Immunotherapy, by MRI-Guided Convective Delivery for the Treatment of Recurrent Glioblastoma

https://digitalcommons.psjhealth.org/other_pubs/1047/thumbnail.jp

Upregulation of the Oct3/4 network in basal breast cancer is associated with its metastatic potential and shows tissue dependent variability

Adaptive plasticity of Breast Cancer stem cells (BCSCs) is strongly correlated with cancer progression and resistance, leading to a poor prognosis. In this study, we report the expression profile of several pioneer transcription factors of th

Effect of graded posterior element and ligament removal on annulus stress and segmental stability in lumbar spine stenosis: a finite element analysis study

The study aimed to investigate the impact of posterior element and ligament removal on the maximum von Mises stress, and maximum shear stress of the eight-layer annulus for treating stenosis at the L3-L4 and L4-L5 levels in the lumbar spine. Previous studies have indicated that laminectomy alone can result in segmental instability unless fusion is performed. However, no direct correlations have been established regarding the impact of posterior and ligament removal. To address this gap, four models were developed: Model 1 represented the intact L2-L5 model, while model 2 involved a unilateral laminotomy involving the removal of a section of the L4 inferior lamina and 50% of the ligament flavum between L4 and L5. Model 3 consisted of a complete laminectomy, which included the removal of the spinous process and lamina of L4, as well as the relevant connecting ligaments between L3-L4 and L4-L5 (ligament flavum, interspinous ligament, supraspinous ligament). In the fourth model, a complete laminectomy with 50% facetectomy was conducted. This involved the same removals as in model 3, along with a 50% removal of the inferior/superior facets of L4 and a 50% removal of the facet capsular ligaments between L3-L4 and L4-L5. The results indicated a significant change in the range of motion (ROM) at the L3-L4 and L4-L5 levels during flexion and torque situations, but no significant change during extension and bending simulation. The ROM increased by 10% from model 1 and 2 to model 3, and by 20% to model 4 during flexion simulation. The maximum shear stress and maximum von-Mises stress of the annulus and nucleus at the L3-L4 levels exhibited the greatest increase during flexion. In all eight layers of the annulus, there was an observed increase in both the maximum shear stress and maximum von-Mises stress from model 1&2 to model 3 and model 4, with the highest rate of increase noted in layers 7&8. These findings suggest that graded posterior element and ligament removal have a notable impact on stress distribution and range of motion in the lumbar spine, particularly during flexion

Development of a biomarker for Geobacter activity and strain composition: Proteogenomic analysis of the citrate synthase protein during bioremediation of U(VI)

Monitoring the activity of target microorganisms during stimulated bioremediation is a key problem for the development of effective remediation strategies. At the US Department of Energy's Integrated Field Research Challenge (IFRC) site in Rifle, CO, the stimulation of Geobacter growth and activity via subsurface acetate addition leads to precipitation of U(VI) from groundwater as U(IV). Citrate synthase (gltA) is a key enzyme in Geobacter central metabolism that controls flux into the TCA cycle. Here, we utilize shotgun proteomic methods to demonstrate that the measurement of gltA peptides can be used to track Geobacter activity and strain evolution during in situ biostimulation. Abundances of conserved gltA peptides tracked Fe(III) reduction and changes in U(VI) concentrations during biostimulation, whereas changing patterns of unique peptide abundances between samples suggested sample-specific strain shifts within the Geobacter population. Abundances of unique peptides indicated potential differences at the strain level between Fe(III)-reducing populations stimulated during in situ biostimulation experiments conducted a year apart at the Rifle IFRC. These results offer a novel technique for the rapid screening of large numbers of proteomic samples for Geobacter species and will aid monitoring of subsurface bioremediation efforts that rely on metal reduction for desired outcomes

Detection of hexavalent uranium with inline and field-portable immunosensors

An antibody that recognizes a chelated form of hexavalent uranium was used in the development of two different immunosensors for uranium detection. Specifically, these sensors were utilized for the analysis of groundwater samples collected during a 2007 field study of in situ bioremediation in a aquifer located at Rifle, CO. The antibody-based sensors provided data comparable to that obtained using Kinetic Phosphorescence Analysis (KPA). Thus, these novel instruments and associated reagents should provide field researchers and resource managers with valuable new tools for on-site data acquisition