Adjacent Disc Research Articles

Biomechanical Analysis of the External Fixation in a Lumbar Fracture Model: A Finite Element Study

PurposeThis study aimed to investigate the biomechanical characteristics of the external spinal fixation for treating lumbar fracture through finite element analysis (FEA) and provide a theoretical basis for its further application.MethodsTwo different models of L3 fracture fixed with the external spinal fixation and the internal fixation system respectively were constructed. The ROM, maximum stresses at L3, and the screws of the two models were measured under load control. Subsequently, the applied torque, the maximum stressed at L3, L1/2, L2/3, L3/4, L4/5 discs and the screws were analyzed under displacement control.ResultsUnder load control, the external fixation model reserved more ROM than the internal fixation model (40.4–48.0% vs 30.5–41.0%). Compared to the internal fixation model, the maximum stresses at L3 and screws in the external fixation model were increased. Under displacement control, the external fixation model required fewer moments (N·mm) than the internal fixation model (flexion: 7500 vs 12,294; extension: 7500 vs 9027). Further, the maximum stresses at L3 and the screws in the external fixation model were greater than those of the internal fixation model, while the maximum stresses at the upper and lower adjacent discs of fixed segments were less than the internal fixation model.ConclusionCompared to the internal fixation system, the external fixation has a better stress distribution with the greater overall mobility. It theoretically reduces the stress concentration of the adjacent discs and the stress shielding of the fractured vertebral body.

Biomechanical Effects of a Novel Anatomic Titanium Mesh Cage for Single-Level Anterior Cervical Corpectomy and Fusion: A Finite Element Analysis.

Background: The traditional titanium mesh cage (TTMC) has become common as a classical instrument for Anterior Cervical Corpectomy and Fusion (ACCF), but a series of complications such as cage subsidence, adjacent segment degeneration (ASD), and implant-related complications by using the TTMC have often been reported in the previous literature. The aim of this study was to assess whether a novel anatomic titanium mesh cage (NTMC) could improve the biomechanical condition after surgery. Methods: The NTMC model consists of two spacers located on both sides of the TTMC which match the anatomic structure between the endplates by measuring patient preoperative cervical computed tomography (CT) data. The ranges of motion (ROMs) of the surgical segments and the stress peaks in the C6 superior endplates, titanium mesh cage (TMC), screw–bone interface, anterior titanium plate, and adjacent intervertebral disc were compared. Results: Compared with the TTMC, the NTMC reduced the surgical segmental ROMs by 89.4% postoperatively. The C6 superior endplate stress peaks were higher in the TTMC (4.473–23.890 MPa), followed by the NTMC (1.923–5.035 MPa). The stress peaks on the TMC were higher in the TTMC (47.896–349.525 MPa), and the stress peaks on the TMC were lower in the NTMC (17.907–92.799 MPa). TTMC induced higher stress peaks in the screw–bone interface (40.0–153.2 MPa), followed by the NTMC (14.8–67.8 MPa). About the stress peaks on the anterior titanium plate, the stress of TTMC is from 16.499 to 58.432 MPa, and that of the NTMC is from 12.456 to 34.607 MPa. Moreover, the TTMC induced higher stress peaks in the C3/4 and C6/7 intervertebral disc (0.201–6.691 MPa and 0.248–4.735 MPa, respectively), followed by the NTMC (0.227–3.690 MPa and 0.174–3.521 MPa, respectively). Conclusion: First, the application of the NTMC can effectively decrease the risks of TMC subsidence after surgery. Second, in the NTMC, the stresses at the anterior screw-plate, bone–screw, and TMC interface are much less than in the TTMC, which decreased the risks of instrument-related complications after surgery. Finally, increases in IDP at adjacent levels are associated with the internal stresses of adjacent discs which may lead to ASD; therefore, the NTMC can effectively decrease the risks of ASD.

Effects of Repulsion and Attraction between Rotating Cylinders in Fluids

Relevance. From the theory of hydrodynamics, it is known about the interaction of a pair of vortices in inviscid fluids. The relevance of the study is conditioned upon the presence of many studies of numerical simulations of the interactions of two vortices or two cylinders, but the lack of research of practical installations for observing the effects of attraction and repulsion in fluid media may slow down research in this area for practical application. Purpose. The purpose of this study is a practical demonstration of the possibility of the effect of double interaction in the air, with the calculation of the approximate magnitude of the force tending to attract or repel each of the cylinders. Methods. In a practical experiment, a pair of plastic cylinders are used, which are driven by engines and rotate next to each other in the air at atmospheric pressure. Numerical simulation of the effect shows the nature of the effect and allows predicting the magnitude of the force generated by rotating cylinders on each other. The relationship between the directions of rotation of the cylinders and the observed effects was verified by numerical simulation using numerical simulation of finite volumes of OpenFOAM version 9. Results. In a practical experiment, a pair of rotating cylinders started interacting at 5-7 cm in the experiment, which at a smaller distance of 2-3 cm created sufficient force to stabilise the vibrations of one of the cylinders around the thread for which it is suspended. Numerical simulation shows that a zone of high or low pressure is formed in the space between the cylinders, depending on the direction of rotation. The rotation of adjacent disks with opposite directions of rotation helps the circulation of the other cylinder to maintain the flow velocity in the gap, which reduces the fluid pressure between the rotating disks and attracts them. Conversely, rotating disks with the same direction extinguish and compress fluid flows in the gap, which increases the air pressure between rotating objects above the stationary pressure and repels them. Conclusions. The results of the study provide a better understanding of the processes of fluid interaction, link the dependence of the interaction force on the parameters of the medium and cylinders, and demonstrate the practical possibility of applying the effects of interaction in fluid media

Do we have to pursue complete reduction after PVA in osteoporotic vertebral compression fractures: a finite element analysis

BackgroundConsensus regarding the optimal amount of bone cement and vertebral height in the treatment of osteoporotic vertebral compression fractures (OVCFs) is lacking. Our purpose was to explore the optimal amount of bone cement and vertebral height in OVCF after percutaneous vertebral augmentation (PVA). MethodsA three-dimensional finite element model of the L1-L3 segments was constructed from CT scans of aging osteoporosis patients. Four different postoperative vertebral height models were simulated according to Genant semiquantitative grades 0, 1, 2, and 3. The volume of bone cement filling ranged from 3 ml to 6 ml. These models evaluated the von Mises stress of injured vertebral bodies, adjacent vertebral bodies and intervertebral discs under flexion, extension, left flexion, and right flexion after PVA. ResultsWhen the bone cement content was held constant, as the height of the vertebral body decreased, the stress of the L2 vertebral body decreased during left flexion and right flexion, but the stress of the L2 vertebral body increased and decreased during flexion and extension. As the height of the vertebral body decreased, the stress of the L1-L2 intervertebral disc increased. There was no significant change in the stress of other adjacent vertebrae or intervertebral discs. When the Genant grade was 0, 1, or 2 (3 ml and 4 ml), the stress of the overall vertebral body was closest to normal. ConclusionsWhen the height of the vertebral body is restored to the same height, a bone cement filling volume of 3 ml to 6 ml is suitable and will not produce a significant change in the stress of the vertebral body or adjacent vertebral body. As vertebral body height was lost, it may promote the degeneration of the intervertebral disc above the injury vertebrae after PVA. It is appropriate for the height of the vertebral body to return to Genant grade 0 or Genant grade 1 after surgery. When the height of the vertebral body has Genant grade 2 status, it was best to use 3 ml to 4 ml of bone cement filling. Therefore, when treating OVCFs, clinicians do not need to pursue complete reduction of the vertebral body. It is also important to verify the biomechanics results in clinical studies.

Измерение деформации поврежденных сегментов в грудном и поясничном отделах позвоночника по данным спиральной компьютерной томографии для расчета необходимой коррекции

Introduction The more accurate is the measurement of the parameters for correcting the deformity of damaged spinal segments the more accurate will be the restoration of the sagittal profile and original anatomy of the spine. Purpose Substantiation of calculated indicators for deformity correction in one or two damaged spinal motion segments in the thoracic and lumbar spine according to spiral computed tomography. Material and methods The material for the study was the results of spiral computed tomography (SCT) of an anatomically unchanged thoracic and lumbar spine in 25 patients (12 women and 13 men aged 18 to 60 years). The study model consisted of three vertebral bodies and four adjacent discs from T4 to L4. Anterior and posterior dimensions of the vertebral bodies, intervertebral discs, and segmental deformity angle α (formed by the lower endplate of the overlying vertebra and the upper endplate of the underlying vertebra) were measured using RadiAnt computer software in the midsagittal projection. Damage to the body of the middle vertebra with adjacent discs was modeled, the dimensions of which were calculated from the adjacent vertebral bodies and adjacent discs. Statistical processing of the material was carried out using the computer software SPSS Statistics. Results The measurement error of the anterior interbody spaces was 1.4 ± 0.4 mm, the posterior interbody spaces were 1.3 ± 0.5 mm, the error in calculating the segmental deformation angle α was 2.5 ± 0.6 degrees, what indicates the high accuracy of the proposed method. Discussion The use of absolute deformity values as a standard for surgical intervention in the treatment of vertebral fractures is complicated by varieties of normal anatomy. Conclusion The proposed calculations for the restoration of the anterior and posterior interbody distances, as well as the angle of segmental deformity α after a spinal cord injury of the thoracic and lumbar spine provide an approach to the target individualized anatomical dimensions.

Adjacent segments biomechanics following lumbar fusion surgery: a musculoskeletal finite element model study.

This study exploits a novel musculoskeletal finite element (MS-FE) spine model to evaluate the post-fusion (L4-L5) alterations in adjacent segment kinetics. Unlike the existing MS models with idealized representation of spinal joints, this model predicts stress/strain distributions in all passive tissues while organically coupled to a MS model. This generic (in terms of musculature and material properties) model uses population-based in vivo vertebral sagittal rotations, gravity loads, and an optimization algorithm to calculate muscle forces. Simulations represent individuals with an intact L4-L5, a preoperative severely degenerated L4-L5 (by reducing the disc height by ~ 60% and removing the nucleus incompressibility), and a postoperative fused L4-L5 segment with either a fixed or an altered lumbopelvic rhythm with respect to the intact condition (based on clinical observations). Changes in spine kinematics and back muscle cross-sectional areas (due to intraoperative injuries) are considered based on in vivo data while simulating three activities in upright/flexed postures. Postoperative changes in some adjacent segment kinetics were found considerable (i.e., larger than 25%) that depended on the postoperative lumbopelvic kinematics and preoperative L4-L5 disc condition. Postoperative alterations in adjacent disc shear, facet/ligament forces, and annulus stresses/strains were greater (> 25%) than those found in intradiscal pressure and compression (< 25%). Kinetics of the lower (L5-S1) and upper (L3-L4) adjacent segments were altered to different degrees. Alterations in segmental rotations mainly affected adjacent disc shear forces, facet/ligament forces, and annulus/collagen fibers stresses/strains. An altered lumbopelvic rhythm (increased pelvis rotation) tends to mitigate some of these surgically induced changes.

Percutaneous endoscopic lumbar discectomy in the treatment of adjacent segment lumbar disc herniation after lumbar fusion

To explore the clinical effect of percutaneous endoscopic lumbar discectomy in the treatment of adjacent segment lumbar disc herniation after lumbar fusion. From February 2010 to June 2018, 64 patients with adjacent segment lumbar disc herniation after lumbar fusion were retrospectively analyzed and divided into observation group and control group. In observation group, there were 23 males and 10 females performed with percutaneous endoscopic lumbar discectomy, including 27 cases of single segment fusion and 6 cases of double segment fusion, aged from 55 to 83 years old with an average of (65.7±7.4) years old. In control group, there were 22 males and 9 females performed with traditional open fusion revision, including 25 cases of single-segment fusion and 6 cases of double segment fusion, aged from 51 to 78 years old with an average of(64.8±7.8) years old. The operative time, intraoperative blood loss, fluoroscopy times, postoperative ambulation time and length of postoperative hospital stay were recorded. The clinical efficacy was evaluated by visual analogue scale(VAS) and Oswestry Disability Index(ODI). The complications between two groups were observed. All patients were followed up for at least 2 years. The observation group patients were followed up with an average of (2.4±0.5) years. The control group patients were followed up with an average of(2.6±0.7) years. Compared with control group, operation time, intraoperative blood loss, postoperative ambulation time and length of postoperative hospital stay of the observation group were significantly reduced (P<0.05), and the fluoroscopy times of observation group were significantly increased compared with control group(P<0.05). The VAS of low back and lower limb, and ODI at the latest follow-up between two groups were all significantly improved compared to those of pre-operation (P<0.05). The VAS of low back at each point and ODI at 1, 3 months after operation in observation group was significantly reduced compared with control group(P<0.05), however there was no significant difference in VAS for lower limb between two groups (P>0.05). The difference of complications between two groups was statistically significant (P<0.05). Compared with traditional open fusion revision surgery, percutaneous endoscopic lumbar discectomy for the treatment of adjacent segment lumbar disc herniation after lumbar fusion has the advantages of reducing operation time and intra-operative blood loss, shortening ambulation time and the length of postoperative hospital stay, and promoting pain and functional improvement, and decrease incidence of complications. However, long-term clinical efficacy needs further study.

Atypical multifocal spinal tuberculosis mimicking malignancy on MR imaging

Typical spinal tuberculosis affects the continuous vertebral levels and causes narrowing of the adjacent disc space and bone destruction. However, atypical form of spinal tuberculosis is difficult to distinguish from malignancy, leading to misdiagnosis and delay in treatment. Tuberculous spondylitis is a curable disease if permanent neurologic damage were avoided by early diagnosis and prompt treatment.

Intervertebral Disk Health Following Vertebral Body Tethering for Adolescent Idiopathic Scoliosis: A Preliminary Study.

Interest in vertebral body tethering (VBT) as an alternative to posterior spinal fusion for adolescent idiopathic scoliosis (AIS) continues to grow. The purpose of this study was to prospectively assess intervertebral disk health on magnetic resonance imaging (MRI) at 1 year following VBT in AIS patients. AIS patients were enrolled in a prospective surgeon-sponsored Food and Drug Administration (FDA) Investigational Device Exemption (IDE) Study and underwent MRI at 1-year following VBT. All spanned disks and the untethered disks immediately adjacent to the upper instrumented vertebra and lowest instrumented vertebra levels were evaluated according to Pfirrmann grading criteria. Associations between patient factors and preoperative and postoperative disk health and patient-reported outcomes were evaluated. Twenty-two patients were enrolled with a postoperative MRI (25 curves, 188 disks), and 7 patients (7 curves) had both preoperative and postoperative MRIs (67 disks). The mean age was 12.7 years. Most were Risser 0 (65%) and either Sanders Skeletal Maturity Score 3 (35%) or 4 (53%). In the 7 patients with preoperative and postoperative MRI, the mean Pfirrmann grade of the disks spanned by the tether was 1.88 preoperatively and 2.31 postoperatively ( P =0.0075). No statistically significant differences in preoperative versus postoperative Pfirrmann grade were identified in the disks adjacent to the upper or lower instrumented vertebrae. No association was found between patient-reported outcomes and Pfirrmann grade. At 1 year postoperatively, increased degenerative changes in disks spanned by the tether was identifiable on MRI without evidence of adjacent segment disk disease. These changes were not associated with patient-reported outcomes. Level III.

Thermal analysis of side-pumped direct-liquid-cooled Nd: YAG thin-disk lasers

Thermal effects are the main obstacle for side-pumped direct-liquid-cooled Nd: YAG thin-disk lasers (SDNTDLs) to achieve high-power near-diffraction-limited laser output. A multiphysics model is established and several basic understandings are obtained. The temperature distribution of the disk under lateral non-uniform pumping shows that the total reflection transmission of the pump lights in the disk does not result in severe temperature fluctuations. The thickness of the thermal boundary layer is much less than half the thickness of the fluid, indicating that there is no thermal interaction between two adjacent disks. The component analysis of the thermally-induced wavefront aberration (TIWA) reveals that the influence of the fluid’s thermo-optic effect (TOE) which is awful in liquid lasers is not necessarily dominant in SDNTDLS due to the thin thermal boundary layer. When cooled by D2O, the wavefront aberration induced by the disk is much larger than that induced by the fluid. As a result, the TIWA exhibits a distribution of high at both sides and low at the center along the transverse direction of the disk, which is consistent with the experimental results. The wavefront aberration induced by the fluid’s TOE and that induced by the disk’s both TOE and deformation compensate for each other, indicating that the beam quality can be significantly improved by means of design optimization.

Long-Term Follow-Up of Dogs and Cats after Stabilization of Thoracolumbar Instability Using 2-0 UniLock Implants.

Traumatic vertebral fracture or luxation often results in spinal instability requiring surgical stabilization. This study describes the long-term outcome of spinal stabilization using a unilateral 5-hole 2-0 UniLock implant in eight dogs and two cats with trauma-induced thoracolumbar vertebral luxation/subluxation and presumed instability, as assessed by a combination of preoperative radiographs and MRI using a 3-compartment method. The UniLock plate was secured with four monocortical locking screws in adjacent vertebral bodies. Additional pins and facet screws were used in several patients. Postoperative radiographs and MRI studies showed restoration of the main spinal axis in all patients and satisfactory implantation of the screws in the vertebral bodies, with no intrusion in the vertebral canal or in the adjacent intervertebral disc spaces. Neurological status improved in nine patients six weeks postoperatively. Partial implant failure was detected in three patients with no long-term consequences. After 12 months, seven patients reached full recovery with no neurological deficit, two patients were euthanized (including one owing to an unrelated condition), and one remained paraparetic. The results of this study demonstrate that using a 2-0 UniLock implant to stabilize the thoracolumbar spine results in satisfactory long-term recovery in most dogs and cats with traumatic spinal luxation/subluxation and presumed instability. Complications may occur but do not require revision surgery and do not affect clinical outcomes.

Lumbosacral Transitional Vertebra Contributed to Lumbar Spine Degeneration: An MR Study of Clinical Patients.

We aimed to comprehensively characterize degenerative findings associated with various types of lumbosacral transitional vertebra (LSTV) on magnetic resonance images. Three hundred and fifty patients with LSTV (52.3 ± 10.9 years), including 182 Castellvi type I, 107 type II, 43 type III, and 18 type IV, and 179 controls without LSTV (50.6 ± 13.1 years), were studied. Discs, endplates, and posterior vertebral structures were assessed and compared to those of controls for the most caudal three discs on MRIs. There were no differences in degenerative findings between patients with type I LSTV and controls. For types III and IV, the transitional discs had smaller sizes, lower Pfirrmann scores, and lower rates of disc bulging (2.3% and 5.6% vs. 39.1%), osteophytes (2.3% vs. 15.1%), disc herniation (2.3% and 5.6% vs. 31.8%), and Modic changes (2.3% and 5.6% vs. 16.8%) than controls. However, the cranial discs had more severe Pfirrmann scores, disc narrowing and spinal canal narrowing, and greater rates of disc herniation (41.9% and 50.0% vs. 25.7%), endplate defects (27.9% and 33.3% vs. 14.4%) and spondylolisthesis (18.6% vs. 7.3%) than controls. Type II LSTV was associated with degenerative findings in the cranial segments but to a lesser degree, as compared with type III/IV LSTV. Thus, Castellvi type III/IV LSTV predisposed the adjacent spinal components to degeneration and protected the transitional discs. Type II LSTV had significant effects in promoting transitional and adjacent disc degeneration. Type I LSTV was not related to spinal degeneration.

Spinal nerve compression after malunion of vertical sacrum fractures.

Introduction and importanceUnstable pelvic ring injuries often occur in high energy traumas. Vertical sacrum fracture is an associated injury. This report describes a late spinal nerve compression that occurred following surgical reduction and fixation of pelvic ring injuries caused by traumatic L5-S1 disc herniation and malposition of the sacral fracture.Case presentationA 61-year-old female presented with radiculopathy in her right leg after surgical reduction and fixation of a sacral and pelvic fracture. Physical examination revealed numbness and weakness of the right leg. Radiographic studies showed spinal compression caused by a fracture spike from the malunion of the sacrum and protruding disc from the L5/S1 level. The fracture spikes were removed by laminectomy and discectomy after which the patient's condition had improved and she had no recurrent symptoms at the one-year follow-up.Clinical discussionMalunion of a posterior pelvic ring fracture and a herniated adjacent intervertebral disc can cause sacral nerve root compression. This complication can be managed and satisfactory results achieved by surgical intervention.ConclusionTraumatic L5-S1 disc herniation and malposition following surgical reduction and fixation of a sacrum fracture can be avoided. Posterior decompression by laminectomy and discectomy is an effective alternative treatment for patients with this condition.

Chiral biosensing using terahertz twisted chiral metamaterial.

Subwavelength chiral metamaterials with tunable geometries and compositions are essential to advance the development of chiral biochemical samples detection. Here, we report a spatial symmetry breaking chiral terahertz (THz) metamaterial structure with stacked layers of L-shape arranged gold disks as the periodic unit cell. The chiroptical response can be adjusted on-demand by manipulating the number of stacking layers and the twisted angle of the periodic unit between adjacent array layers. We reveal that the chiroptical response originates from the optical resonances of the gold disks and the adjacent gold disks array layers via experiments and numerical simulation analysis. Furthermore, we find that this chiral metamaterial can realize label-free detection of proline in biological samples and label-free enantio-discrimination of chiral molecules. The change of the analyte concentration can also regulate the transmission circular dichroism (TCD) intensity of the chiral metamaterials. Our results not only provide new ideas into the design of functional chiral metamaterials, but also bring new strategies to develop chiroptical biosensing devices.

Adjacent Segment Degeneration after Short-Segment Lateral Lumbar Interbody Fusion (LLIF)

Purpose To investigate the influence on the adjacent segment degeneration (ASD) of short-segment lateral lumbar interbody fusion (LLIF) at 2 years postoperatively. Methods Ninety-seven consecutive patients who underwent one- or two-level LLIF were included from two institutions. We diagnosed radiographical adjacent segment degeneration with the appearance of adjacent spondylolisthesis (>3 mm) or deterioration of adjacent disk height (>3 mm) on plain radiographs or decrease of the intervertebral angle (>5 degrees). The differences between the two groups with and without radiographical ASD were investigated using univariate and multivariate analyses to determine the risk factors for ASD. The variables included extent of adjacent decompression, posterior fixation method (open method or percutaneous method), and facet violation on postoperative CT. Results In total, 19 patients (19.6%) were diagnosed as radiographical ASD 2 years after surgery. Univariate analysis showed that the ASD (+) group had a high frequency of adjacent decompression (21.1 vs. 3.8%, p = 0.035) compared with the ASD (-) group. There were no differences between the two groups in posterior fusion method (percutaneous method 42.1 vs. 57.7%, p = 0.221) or facet joint violation (15.8 vs. 14.1%, p = 0.860). The multivariate analysis found adjacent intervertebral decompression to be a risk factor for ASD 2 years after surgery (odds ratio: 9.95; 95% confidence interval: 1.2–82.1). Conclusions Adjacent intervertebral decompression was considered to be a potential risk factor for the development of ASD after spinal fusion with LLIF.

Biomechanical Evaluation of Intervertebral Fusion Process After Anterior Cervical Discectomy and Fusion: A Finite Element Study.

Introduction: Anterior cervical discectomy and fusion (ACDF) is a widely accepted surgical procedure in the treatment of cervical radiculopathy and myelopathy. A solid interbody fusion is of critical significance in achieving satisfactory outcomes after ACDF. However, the current radiographic techniques to determine the degree of fusion are inaccurate and radiative. Several animal experiments suggested that the mechanical load on the spinal instrumentation could reflect the fusion process and evaluated the stability of implant. This study aims to investigate the biomechanical changes during the fusion process and explore the feasibility of reflecting the fusion status after ACDF through the load changes borne by the interbody fusion cage. Methods: The computed tomography (CT) scans preoperatively, immediately after surgery, at 3 months, and 6 months follow-up of patients who underwent ACDF at C5/6 were used to construct the C2–C7 finite element (FE) models representing different courses of fusion stages. A 75-N follower load with 1.0-Nm moments was applied to the top of C2 vertebra in the models to simulate flexion, extension, lateral bending, and axial rotation with the C7 vertebra fixed. The Von Mises stress at the surfaces of instrumentation and the adjacent intervertebral disc and force at the facet joints were analyzed. Results: The facet contact force at C5/6 suggested a significantly stepwise reduction as the fusion proceeded while the intradiscal pressure and facet contact force of adjacent levels changed slightly. The stress on the surfaces of titanium plate and screws significantly decreased at 3 and 6 months follow-up. A markedly changed stress distribution in extension among three models was noted in different fusion stages. After solid fusion is achieved, the stress was more uniformly distributed interbody fusion in all loading conditions. Conclusions: Through a follow-up study of 6 months, the stress on the surfaces of cervical instrumentation remarkably decreased in all loading conditions. After solid intervertebral fusion formed, the stress distributions on the surfaces of interbody cage and screws were more uniform. The stress distribution in extension altered significantly in different fusion status. Future studies are needed to develop the interbody fusion device with wireless sensors to achieve longitudinal real-time monitoring of the stress distribution during the course of fusion.

Thorough Comparative Analysis of Stand-Alone Cage and Anterior Cervical Plate for Anterior Cervical Discectomy and Fusion in the Treatment of Cervical Degenerative Disease: A Systematic Review and Meta-analysis.

In this systematic review and meta-analysis, we aim to thoroughly describe and objectively compare the efficacy of anterior cervical plate (ACP) and stand-alone cage (SAC). Although recognized as an effective procedure for cervical degenerative disease (CDD), a debate between the methods of anterior cervical discectomy and fusion exists. ACP provides stability to the fusion construct; however, some complications have been reported, such as dysphagia, adjacent disc disease, and soft tissue injury. To overcome these complications, a SAC was later introduced. A systematic search was conducted on the basis of PRISMA (preferred reporting items for systematic reviews and meta-analyses) guidelines to identify relevant studies through PubMed, Google Scholar, and Cochrane database. A total of 14 studies (960 patients) were included in the meta-analysis. Twenty outcomes were clinically and radiologically compared between the two procedures. ACP and SAC were comparable in terms of dysphasia rate, loss of segmental angle, loss of disc height, the Odom criteria, Robinson's criteria, hospital stay, Japanese Orthopaedic Association score, Neck Disability Index, Visual Analog Scale, and fusion time. However, SAC was superior in terms of shorter operation time, less blood loss, lower dysphagia rate, and lower rate of adjacent level disease, whereas ACP was advantageous in terms of lower subsidence rate, better maintenance of the cervical global and segmental angles and disc height, and higher fusion rate. Both procedures can be used in patients with CDD, although it might be more beneficial to choose ACP in patients with multi-level pathologies, wherein better mechanical stability is provided. However, SAC may be more beneficial to use in patients with comorbidities, anemia, or swelling problems because it offers lower complication rates.

Dynamic Modeling of Tie-bolt Rotors via Fractal Contact Theory and Virtual Material Method

Tie-bolt rotors, comprised of multiple stages of discs fastened by tie bolts, are commonly used in heavy-duty gas turbines. The contact interfaces between adjacent discs have considerable influence on the dynamic characteristics of tie-bolt rotors. Although many studies on the modeling of tie-bolt rotors have been reported, it is still a challenge to develop a relatively simple, efficient, and accurate model for such a kind of complex rotors. In this article, a new virtual material modeling method is proposed to analyze the dynamic characteristics of tie-bolt rotors. The elastic modulus and Poisson ratio of the virtual material are determined from the interface contact stiffness, which is derived based on the three-dimensional fractal contact theory. To verify the modeling approach proposed here, modal tests are conducted on a tie-bolt rotor specimen, of which the measured natural frequencies are compared with the simulation results. Finally, by using the verified modeling approach, the dynamic behaviors of tie-bolt rotors are investigated comprehensively, where the effects of fractal dimension parameters and preload level on rotor dynamics are evaluated.

Changes in quantitative elastography assessment of the adjacent lumbar disc after segmental fixation of the spine: a case description of a burst fracture of L4.

Raphaël Pietton, Raphaël Vialle, Romain Laurent, Wafa Skalli, Claudio Vergari, Tristan Langlais

A Pain in the Neck: An Adolescent with Neck Pain.

A Pain in the Neck: An Adolescent with Neck Pain.