scholarly journals A Hybrid Uniplanar Pedicle Screw System with a New Intermediate Screw for Minimally Invasive Spinal Fixation: A Finite Element Analysis

2020 ◽  
Vol 2020 ◽  
pp. 1-9
Author(s):  
Jia Li ◽  
Li-Cheng Zhang ◽  
Jiantao Li ◽  
Hao Zhang ◽  
Jing-Xin Zhao ◽  
...  
Keyword(s):  
Finite Element ◽  
Minimally Invasive ◽  
Range Of Motion ◽  
Pedicle Screw ◽  
Axial Rotation ◽  
Von Mises Stress ◽  
Spinal Fixation ◽  
Lateral Bending ◽  
Maximum Displacement ◽  
Von Mises

Purpose. A hybrid pedicle screw system for minimally invasive spinal fixation was developed based on the uniplanar pedicle screw construct and a new intermediate screw. Its biomechanical performance was evaluated using finite element (FE) analysis. Methods. A T12-L2 FE model was established to simulate the L1 vertebral compression fracture with Magerl classification A1.2. Six fixation models were developed to simulate the posterior pedicle screw fracture fixation, which were divided into two subgroups with different construct configurations: (1) six-monoaxial/uniplanar/polyaxial pedicle screw constructs and (2) four-monoaxial/uniplanar/polyaxial pedicle screw constructs with the new intermediate screw. After model validation, flexion, extension, lateral bending, and axial rotation with 7.5 Nm moments and preloading of 500 N vertical compression were applied to the FE models to compare the biomechanical performances of the six fixation models with maximum von Mises stress, range of motion, and maximum displacement of the vertebra. Results. Under four loading scenarios, the maximum von Mises stresses were found to be at the roots of the upper or lower pedicle screws. In the cases of flexion, lateral bending, and axial rotation, the maximum von Mises stress of the uniplanar screw construct lay in between the monoaxial and polyaxial screw constructs in each subgroup. Considering lateral bending, the uniplanar screw construct enabled to lower the maximum von Mises stress than monoaxial and polyaxial pedicle screw constructs in each subgroup. Two subgroups showed comparable results of the maximum von Mises stress on the endplates, range of motion of T12-L1, and maximum displacement of T12 between the corresponding constructs with the new intermediate screw or not. Conclusions. The observations shown in this study verified that the hybrid uniplanar pedicle screw system exhibited comparable biomechanical performance as compared with other posterior short-segment constructs. The potential advantage of this new fixation system may provide researchers and clinical practitioners an alternative for minimally invasive spinal fixation with vertebral augmentation.

Design and development of a novel expanding flexible rod device (FRD) for stability in the lumbar spine: A finite-element study

2020 ◽  
Vol 43 (12) ◽  
pp. 803-810 ◽  
Author(s):  
Masud Rana ◽  
Sandipan Roy ◽  
Palash Biswas ◽  
Shishir Kumar Biswas ◽  
Jayanta Kumar Biswas
Keyword(s):  
Finite Element ◽  
Lumbar Spine ◽  
Range Of Motion ◽  
Pedicle Screw ◽  
Axial Rotation ◽  
Von Mises Stress ◽  
Lateral Bending ◽  
Intact Bone ◽  
Flexion Extension ◽  
Von Mises

The aim of this study is to design a novel expanding flexible rod device, for pedicle screw fixation to provide dynamic stability, based on strength and flexibility. Three-dimensional finite-element models of lumbar spine (L1-S) with flexible rod device on L3-L4-L5 levels are developed. The implant material is taken to be Ti-6Al-4V. The models are simulated under different boundary conditions, and the results are compared with intact model. In natural model, total range of motion under 10 Nm moment were found 66.7°, 24.3° and 13.59°, respectively during flexion–extension, lateral bending and axial rotation. The von Mises stress at intact bone was 4 ± 2 MPa and at bone, adjacent to the screw in the implanted bone, was 6 ± 3 MPa. The von Mises stress of disc of intact bone varied from 0.36 to 2.13 MPa while that of the disc between the fixed vertebra of the fixation model reduced by approximately 10% for flexion and 25% for extension compared to intact model. The von Mises stresses of pedicle screw were 120, 135, 110 and 90 MPa during flexion, extension, lateral bending, and axial rotation, respectively. All the stress values were within the safe limit of the material. Using the flexible rod device, flexibility was significantly increased in flexion/extension but not in axial rotation and lateral bending. The results suggest that dynamic stabilization system with respect to fusion is more effective for homogenizing the range of motion of the spine.

scholarly journals Biomechanical feasibility of semi-rigid stabilization and semi-rigid lumbar interbody fusion: a finite element study

2022 ◽  
Vol 23 (1) ◽  
Author(s):  
Chia-En Wong ◽  
Hsuan-Teh Hu ◽  
Li-Hsing Kao ◽  
Che-Jung Liu ◽  
Ke-Chuan Chen ◽  
...  
Keyword(s):  
Finite Element ◽  
Strain Energy ◽  
Lumbar Fusion ◽  
Axial Rotation ◽  
Von Mises Stress ◽  
Peek Cage ◽  
Lateral Bending ◽  
Interspinous Spacer ◽  
Flexion Extension ◽  
Von Mises

Abstract Background Semi-rigid lumbar fusion offers a compromise between pedicle screw-based rigid fixation and non-instrumented lumbar fusion. However, the use of semi-rigid interspinous stabilization (SIS) with interspinous spacer and ligamentoplasty and semi-rigid posterior instrumentation (SPI) to assist interbody cage as fusion constructs remained controversial. The purpose of this study is to investigate the biomechanical properties of semi-rigidly stabilized lumbar fusion using SIS or SPI and their effect on adjacent levels using finite element (FE) method. Method Eight FE models were constructed to simulate the lumbosacral spine. In the non-fusion constructs, semi-rigid stabilization with (i) semi-rigid interspinous spacer and artificial ligaments (PD-SIS), and (ii) PI with semi-rigid rods were simulated (PD + SPI). For fusion constructs, the spinal models were implanted with (iii) PEEK cage only (Cage), (iv) PEEK cage and SIS (Cage+SIS), (v) PEEK cage and SPI (Cage+SPI), (vi) PEEK cage and rigid PI (Cage+PI). Result The comparison of flexion-extension range of motion (ROM) in the operated level showed the difference between Cage+SIS, Cage+SPI, and Cage+PI was less than 0.05 degree. In axial rotation, ROM of Cage+SIS were greater than Cage+PI by 0.81 degree. In the infrajacent level, while Cage+PI increased the ROM by 24.1, 27,7, 25.9, and 10.3% and Cage+SPI increased the ROM by 26.1, 30.0, 27.1, and 10.8% in flexion, extension, lateral bending and axial rotation respectively, Cage+SIS only increased the ROM by 3.6, 2.8, and 11.2% in flexion, extension, and lateral bending and reduced the ROM by 1.5% in axial rotation. The comparison of the von Mises stress showed that SIS reduced the adjacent IVD stress by 9.0%. The simulation of the strain energy showed a difference between constructs less than 7.9%, but all constructs increased the strain energy in the infradjacent level. Conclusion FE simulation showed semi-rigid fusion constructs including Cage+SIS and Cage+SPI can provide sufficient stabilization and flexion-extension ROM reduction at the fusion level. In addition, SIS-assisted fusion resulted in less hypermobility and less von Mises stress in the adjacent levels. However, SIS-assisted fusion had a disadvantage of less ROM reduction in lateral bending and axial rotation. Further clinical studies are warranted to investigate the clinical efficacy and safety of semi-rigid fusions.

Rod Stress Prediction in Spinal Alignment Surgery With Different Supplementary Rod Constructing Techniques: A Finite Element Study

2018 ◽  
Author(s):  
Ming Xu ◽  
Thomas Scholl ◽  
Pedro Berjano ◽  
Jazmin Cruz ◽  
James Yang
Keyword(s):  
Finite Element ◽  
Contact Region ◽  
Element Model ◽  
Axial Rotation ◽  
Von Mises Stress ◽  
Lateral Bending ◽  
Flexion Extension ◽  
Single Cross ◽  
Von Mises ◽  
Double Cross

Rod fracture and nonunion are common complications associated with pedicle subtraction osteotomies (PSO). Supplementary rods and interbody cage (IB) are added to reduce the primary rod stress. As supplementary rods, delta rods and cross rods have been proposed to reduce more stress on the primary rods compared to conventional supplementary rods (accessary rods) in PSO. The objective of this study is to investigate the effects of cross rods and delta rods on reducing primary rod stress in PSO subject. A validated 3D finite element model of a T12-S1 spine segment with 25° PSO at L3 and bilateral rods fixation from T12-S1 was used to compare different rod configurations: 1) PSO and two primary rods (PSO+2P); 2) PSO with an IB at L2-L3 (PSO+2P+IB); 3) PSO with accessory rods and an IB at L2-L3 (PSO+2P+IB+2A); 4) PSO with delta rods and an IB at L2-L3 (PSO+2P+IB+2D); 5) PSO with single cross rod and an IB at L2-L3 (PSO+2P+IB+1C); 6) PSO with double cross rods and an IB at L2-L3 (PSO+2P+IB+2C). The spine model was loaded with a follower load of 400 N combined with pure moments of 7.5 Nm in flexion, extension, right lateral bending, and right axial rotation. Von Mises stress of the primary rods were predicted for all test conditions. The PSO without IB condition had the largest primary rod stress in flexion. With IB at L2-L3, the rod stress in flexion reduced by 15%. Adding 2 conventional supplementary rods reduced the rod stress in flexion by 29%, which was achieved by adding single cross rod. The maximum von Mises stress occurred in the middle of the primary rods without supplementary rods whereas the maximum stress concentrated adjacent to the contact region between the connectors and the primary rods. Delta rods and double cross rods reduced the most rod stress in flexion, which were by 33% and 32% respectively. Under lateral bending, 2 delta rods reduced the most primary rod stress (−33%). Under axial rotation, the single cross rod reduced the most primary rod stress (−48%). Interbody cages and supplementary rods reduced the primary rod stress in a comparable way. Primary rod stress with 2 delta rods and double cross rods were comparable, which were marginally lower than those with conventional supplementary rods. Adding single cross rod was comparable to adding 2 conventional accessory rods in rod stress reduction in flexion. Under lateral bending, delta rods reduced most rod stress whereas under axial rotation, cross rods reduced most rod stress. This study suggested that both delta rods and cross rods reduce more primary rod stress than conventional accessory rods do.

How the height and the area of the annulus fibrosus affect the range of motion behavior: A stochastic analysis

2018 ◽  
Vol 233 (10) ◽  
pp. 1985-1992
Author(s):  
Héctor E Jaramillo S
Keyword(s):  
Finite Element ◽  
Range Of Motion ◽  
Annulus Fibrosus ◽  
Element Model ◽  
Axial Rotation ◽  
Disc Height ◽  
Lateral Bending ◽  
Analytic Equation ◽  
Geometrical Properties ◽  
Flexion Extension

The annulus fibrosus has substantial variations in its geometrical properties (among individuals and between levels), and plays an important role in the biomechanics of the spine. Few works have studied the influence of the geometrical properties including annulus area, anterior / posterior disc height, and over the range of motion, but in general these properties have not been reported in the finite element models. This paper presents a probabilistic finite element analyses (Abaqus 6.14.2) intended to assess the effects of the average disc height ( hp) and the area ( A) of the annulus fibrosus on the biomechanics of the lumbar spine. The annulus model was loaded under flexion, extension, lateral bending, and axial rotation and analyzed for different combinations of hpand A in order to obtain their effects over the range of motion. A set of 50 combinations of hp(mean = 18.1 mm, SD = 3.5 mm) and A (mean = 49.8%, SD = 4.6%) were determined randomly according to a normal distribution. A Yeoh energy function was used for the matrix and an exponential function for the fibers. The range of motion was more sensitive to hpthan to A. With regard to the range of motion the segment was more sensitive in the following order: flexion, axial rotation, extension, and lateral bending. An increase of the hpproduces an increase of the range of motion, but this decreases when A increases. Comparing the range of motion with the experimental data, on average, 56.0% and 73.0% of the total of data were within the experimental range for the L4–L5 and L5–S1 segments, respectively. Further, an analytic equation was derived to obtain the range of motion as a function of the hpand A. This equation can be used to calibrate a finite element model of the spine segment, and also to understand the influence of each geometrical parameter on the range of motion.

scholarly journals Design of a Dynamic Stabilization Spine Implant

2009 ◽  
Vol 3 (2) ◽  
Author(s):  
J. Bryndza ◽  
A. Weiser ◽  
M. Paliwal
Keyword(s):  
Finite Element ◽  
Range Of Motion ◽  
Mechanical Testing ◽  
Computational Analysis ◽  
Axial Rotation ◽  
Dynamic Stabilization ◽  
Facet Joints ◽  
Lateral Bending ◽  
Functional Spinal Unit ◽  
Flexion Extension

Arthritis, degenerative disc disease, spinal stenosis, and other ailments lead to the deterioration of the facet joints of the spine, causing pain and immobility in patients. Dynamic stabilization and arthroplasty of the facet joints have advantages over traditional fusion methods by eliminating pain while maintaining normal mobility and function. In the present work, a novel dynamic stabilization spine implant design was developed using computational analysis, and the final design was fabricated and mechanically tested. A model of a fused L4–L5 Functional Spinal Unit (FSU) was developed using Pro/Engineer (PTC Corporation, Needham, MA). The model was imported into commercial finite element analysis software Ansys (Ansys Inc., Canonsburg, PA), and meshed with the material properties of bone, intervertebral disc, and titanium alloy. Physiological loads (600N axial load, 10 N-m moment) were applied to the model construct following the protocol developed by others. The model was subjected to flexion/extension, axial rotation, and lateral bending, and was validated with the results reported by Kim et al. The validated FSU was used as a base to design and evaluate novel spine implant designs, using finite element anlysis. A comparison of the flexion-extension curve of six designs and an intact spine was carried out. Range of motion of the new designs showed up to 4 degrees in flexion and extension, compared to less than one degree flexion/extension in a fused spine. The design that reproduced normal range of motion best was optimized, fabricated and prepared for mechanical testing. The finalized dynamic stabilization design with spring insert was implanted into a L4-L5 FSU sawbone (Pacific Research Laboratories, Vashon, WA) using Stryker Xia pedicle screws. The construct was potted using PMMA, and was subjected to flexion/extension, axial rotation, and lateral bending loads using MTS mechanical testing machine. The stiffness of the design was assessed and compared with computational analysis results.

scholarly journals Effects of Revision Rod Position on Spinal Construct Stability in Lumbar Revision Surgery: A Finite Element Study

2022 ◽  
Vol 9 ◽  
Author(s):  
Quan-Chang Tan ◽  
Jin-Feng Huang ◽  
Hao Bai ◽  
Zi-Xuan Liu ◽  
Xin-Yi Huang ◽  
...  
Keyword(s):  
Finite Element ◽  
Revision Surgery ◽  
Spinal Instrumentation ◽  
Axial Rotation ◽  
Von Mises Stress ◽  
Fe Model ◽  
Interspinous Ligament ◽  
Moment Load ◽  
Von Mises ◽  
Changing Tendency

Revision surgery (RS) is a necessary surgical intervention in clinical practice to treat spinal instrumentation–related symptomatic complications. Three constructs with different configurations have been applied in RS. One distinguishing characteristic of these configurations is that the revision rods connecting previous segments and revision segments are placed alongside, outside, or inside the previous rods at the level of facetectomy. Whether the position of the revision rod could generate mechanical disparities in revision constructs is unknown. The objective of this study was to assess the influence of the revision rod position on the construct after RS. A validated spinal finite element (FE) model was developed to simulate RS after previous instrumented fusion using a modified dual-rod construct (DRCm), satellite-rod construct (SRC), and cortical bone trajectory construct (CBTC). Thereafter, maximum von Mises stress (VMS) on the annulus fibrosus and cages and the ligament force of the interspinous ligament, supraspinous ligament, and ligamentum flavum under a pure moment load and a follower load in six directions were applied to assess the influence of the revision rod position on the revision construct. An approximately identical overall reducing tendency of VMS was observed among the three constructs. The changing tendency of the maximum VMS on the cages placed at L4-L5 was nearly equal among the three constructs. However, the changing tendency of the maximum VMS on the cage placed at L2-L3 was notable, especially in the CBTC under right bending and left axial rotation. The overall changing tendency of the ligament force in the DRCm, SRC, and CBTC was also approximately equal, while the ligament force of the CBTC was found to be significantly greater than that of the DRCm and SRC at L1-L2. The results indicated that the stiffness associated with the CBTC might be lower than that associated with the DRCm and SRC in RS. The results of the present study indicated that the DRCm, SRC, and CBTC could provide sufficient stabilization in RS. The CBTC was a less rigid construct. Rather than the revision rod position, the method of constructing spinal instrumentation played a role in influencing the biomechanics of revision.

Biomechanical Comparison of Vertbroplasty, Kyphoplasty, Vertebrae Stent for Osteoporotic Vertebral Compression Fractures -A Finite Element Analysis

2021 ◽  
Author(s):  
Jen-Chung Liao ◽  
Michael Jian-Wen Chen ◽  
Tung-Yi Lin ◽  
Weng-Pin Chen
Keyword(s):  
Finite Element ◽  
Body Height ◽  
Compressive Force ◽  
Axial Rotation ◽  
Vertebral Compression Fractures ◽  
Lateral Bending ◽  
Compression Fractures ◽  
Significant Difference ◽  
Von Mises ◽  
Von Mises Stresses

Abstract Vertebroplasty (VP), balloon kyphoplasty (BKP), and vertebral stent (VS) are usually used for osteoporotic compression fracture. However, these procedures may pose risks of secondary adjacent level fractures. This study simulates finite element models of osteoporotic compression fractures treated with VP, BKP, and VS. Vertebral resection method was used to simulate vertebra fracture with Young’s modulus set at 70 MPa to replicate osteoporosis. A compressive force of 1000N was applied on the T11 vertebra while the L1 vertebra were fully constrained as boundary condition. Moment loadings of 4.2 N-m in flexion, 1.0 N-m in extension, 2.6 N-m in lateral bending, and 3.4 N-m in axial rotation were applied. The VS model had the highest von Mises stresses on the bone cement under all different loading conditions (flexion/5.91 Mpa; extension/3.74 Mpa; lateral bending/3.12 Mpa; axial rotation/3.54 Mpa). The stress distribution and maximum von Mises stresses of the adjacent segments, T11 inferior endplate and L1 superior endplate, showed no significant difference among three surgical models. The postoperative T12 stiffness for VP, BKP, and VS are 2898.48 N/mm, 4123.18 N/mm, and 4690.34 N/mm, respectively. VS is the most effective surgical method to maintain vertebral body height without significantly increasing the risks of adjacent fracture.

scholarly journals Biomechanical Comparison of Vertebroplasty, Kyphoplasty, Vertebrae Stent for Osteoporotic Vertebral Compression Fractures—A Finite Element Analysis

2021 ◽  
Vol 11 (13) ◽  
pp. 5764
Author(s):  
Jen-Chung Liao ◽  
Michael Jian-Wen Chen ◽  
Tung-Yi Lin ◽  
Weng-Pin Chen
Keyword(s):  
Finite Element ◽  
Axial Rotation ◽  
Vertebral Compression Fractures ◽  
Lateral Bending ◽  
Compression Fractures ◽  
Significant Difference ◽  
Flexion Extension ◽  
Von Mises ◽  
Von Mises Stresses ◽  
Osteoporotic Compression Fractures

Vertebroplasty (VP), balloon kyphoplasty (BKP), and vertebral stent (VS) are usually used for treating osteoporotic compression fractures. However, these procedures may pose risks of secondary adjacent level fractures. This study simulates finite element models of osteoporotic compression fractures treated with VP, BKP, and VS Vertebral resection method was used to simulate vertebra fracture with Young’s modulus set at 70 MPa to replicate osteoporosis. A follower load of (1175 N for flexion, and 500 N for all others) was applied in between vertebral bodies to simulate the muscle force. Moment loadings of 7.5 N-m in flexion, extension, lateral bending, axial rotation were applied respectively. The VS model had the highest von Mises stresses on the bone cement under all different loading conditions (flexion/5.91 MPa; extension/3.74 MPa; lateral bending/3.12 MPa; axial rotation/3.54 MPa). The stress distribution and maximum von Mises stresses of the adjacent segments, T11 inferior endplate and L1 superior endplate, showed no significant difference among three surgical models. The postoperative T12 stiffness for VP, BKP, and VS are 2898.48 N/mm, 4123.18 N/mm, and 4690.34 N/mm, respectively. The VS model led to superior surgical vertebra stiffness without significantly increasing the risks of adjacent fracture.

Comparison of Fatigue Behaviors of Spinal Implants Under Physiological Spinal Loads: A Finite Element Pilot Study

2017 ◽  
Author(s):  
Ming Xu ◽  
James Yang ◽  
Isador H. Lieberman ◽  
Ram Haddas
Keyword(s):  
Pedicle Screw ◽  
Axial Rotation ◽  
Von Mises Stress ◽  
Fe Model ◽  
Fusion Surgery ◽  
Spinal Loads ◽  
Spinal Implants ◽  
Exact Geometry ◽  
Von Mises ◽  
Biomechanical Tests

The fusion surgery is a standard treatment for scoliosis. Fatigue-related failure is one common cause for the fusion surgery implant. Due to the high cost of revision surgery, it is of clinical value to study the fatigue behaviors of the spinal implants under physiological spinal loads. In the literature, biomechanical tests and finite element (FE) methods have been used to study the fatigue of the spinal implants. Compared with biomechanical tests, FE analysis has the advantage of low cost and high efficiency. Due to the high computational cost, no FE study has been modeled the exact geometry of the pedicle screw (including the thread) in the screw-bone connection within the multi-level spine FE model. This study introduced a feasible FE-based method to predict the fatigue behaviors of the spinal implants with exact geometry of pedicle screw. One previously-validated FE spine model was utilized to provide physiological spinal loads and was bilaterally fused with pedicle screws and rods at L3-L4 spine levels. The exact geometry of the pedicle screw was simulated in this study for accurate stress prediction. The fused spine FE model was subjected to six loading directions (flexion/extension, left/right lateral bending, and left/right axial rotation). For each loading direction, a pure bending moment of 10 Nm was tested. First, FE analysis was performed for one loading cycle. Range of motion, maximum von Mises stress values of the spinal implants were recorded and compared for the six tested loading conditions. Then, based on the stress/strain history of the spinal implants for one loading cycle provided by the FE simulation, fatigue life cycles of the spinal implants were calculated using strain-based Smith-Watson-Topper equation. Flexion produced the largest range of motion at the adjacent level. Axial rotation produced the largest von Mises stress in the spinal implants. Except for lateral bending, the von Mises stress predicted in the screws fused at the superior vertebra was larger than that in the screws fused at inferior vertebra. The method introduced in this study will be used to study different screw fixation methods in the future work.

Three Dimensional Finite Element Interference Contact Analysis about Cone Screw and Bush of Opposed Biconinal Cone Screw High-Pressure Seawater Hydraulic Pump

2012 ◽  
Vol 197 ◽  
pp. 174-178 ◽  
Author(s):  
Xin Hua Wang ◽  
Xiu Xia Cao ◽  
Shu Wen Sun ◽  
Yan Gao
Keyword(s):  
Finite Element ◽  
High Pressure ◽  
Displacement Vector ◽  
Three Dimensional ◽  
Von Mises Stress ◽  
Hydraulic Pump ◽  
Maximum Displacement ◽  
Element Analysis ◽  
Factors Affecting ◽  
Von Mises

The main components of the opposed biconinal cone screw high-pressure seawater hydraulic pump is the rubber bush and metal cone screw, and the interaction of the bush and cone screw is one of the main factors affecting the novel pump performance. The deformation and stress of the bush and cone screw under the initial interference is analyzed by the nonlinear finite element analysis. The analysis shows that: under the effect of the initial interference, large displacement is present to the radial surface of the cone screw, and the displacement of the radial surface mainly affects the displacement vector sum of the cone screw, and the deformation decreases gradually from the middle to the ends of the cone screw, while the cone screw is bending; the deformation in three direction of the bush is close to each other, but the location of the maximum displacement in each direction is different; with the shrink range increasing, the deformation of the cone screw and bush increases, but the deformation of the cone screw is much smaller than that of bush, so the deformation of the bush mainly affects the seal between the cone screw and bush, and the shrink range between the cone screw and bush decreases because of the deformation of the bush. Over the role of the interference force, the maximum von mises stress of the cone screw is an order larger than that of bush, and the maximum von mises stress both increases with the shrink range increasing; although shrink range is different, the location of the maximum von mises about the cone screw and bush is the same.

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