scholarly journals The effect of posterior polyester tethers on the biomechanics of proximal junctional kyphosis: a finite element analysis

2017 ◽  
Vol 26 (1) ◽  
pp. 125-133 ◽  
Author(s):  
Shay Bess ◽  
Jeffrey E. Harris ◽  
Alexander W. L. Turner ◽  
Virginie LaFage ◽  
Justin S. Smith ◽  
...  
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Pedicle Screws ◽  
Proximal Segment ◽  
Gradual Transition ◽  
Proximal Junctional Kyphosis ◽  
Element Analysis ◽  
Posterior Ligament Complex ◽  
Posterior Ligament ◽  
Junctional Kyphosis

OBJECTIVE Proximal junctional kyphosis (PJK) remains problematic following multilevel instrumented spine surgery. Previous biomechanical studies indicate that providing less rigid fixation at the cranial aspect of a long posterior instrumented construct, via transition rods or hooks at the upper instrumented vertebra (UIV), may provide a gradual transition to normal motion and prevent PJK. The purpose of this study was to evaluate the ability of posterior anchored polyethylene tethers to distribute proximal motion segment stiffness in long instrumented spine constructs. METHODS A finite element model of a T7–L5 spine segment was created to evaluate range of motion (ROM), intradiscal pressure, pedicle screw loads, and forces in the posterior ligament complex within and adjacent to the proximal terminus of an instrumented spine construct. Six models were tested: 1) intact spine; 2) bilateral, segmental pedicle screws (PS) at all levels from T-11 through L-5; 3) bilateral pedicle screws from T-12 to L-5 and transverse process hooks (TPH) at T-11 (the UIV); 4) pedicle screws from T-11 to L5 and 1-level tethers from T-10 to T-11 (TE-UIV+1); 5) pedicle screws from T-11 to L-5 and 2-level tethers from T-9 to T-11 (TE-UIV+2); and 6) pedicle screws and 3-level tethers from T-8 to T-11 (TE-UIV+3). RESULTS Proximal-segment range of motion (ROM) for the PS construct increased from 16% at UIV−1 to 91% at UIV. Proximal-segment ROM for the TPH construct increased from 27% at UIV−1 to 92% at UIV. Posterior tether constructs distributed ROM at the UIV and cranial adjacent segments most effectively; ROM for TE-UIV+1 was 14% of the intact model at UIV−1, 76% at UIV, and 98% at UIV+1. ROM for TE-UIV+2 was 10% at UIV−1, 51% at UIV, 69% at UIV+1, and 97% at UIV+2. ROM for TE-UIV+3 was 7% at UIV−1, 33% at UIV, 45% at UIV+1, and 64% at UIV+2. Proximal segment intradiscal pressures, pedicle screw loads, and ligament forces in the posterior ligament complex were progressively reduced with increasing number of posterior tethers used. CONCLUSIONS Finite element analysis of long instrumented spine constructs demonstrated that posterior tethers created a more gradual transition in ROM and adjacent-segment stress from the instrumented to the noninstrumented spine compared with all PS and TPH constructs. Posterior tethers may limit the biomechanical risk factor for PJK; however, further clinical research is needed to evaluate clinical efficacy.

Optimal tether configurations and preload tensioning to prevent proximal junctional kyphosis: a finite element analysis

2019 ◽  
Vol 30 (5) ◽  
pp. 574-584 ◽  
Author(s):  
Thomas J. Buell ◽  
Shay Bess ◽  
Ming Xu ◽  
Frank J. Schwab ◽  
Virginie Lafage ◽  
...  
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Element Model ◽  
Adjacent Segment ◽  
Proximal Junctional Kyphosis ◽  
Element Analysis ◽  
Distal Fixation ◽  
Upper Instrumented Vertebra ◽  
The Impact ◽  
Junctional Kyphosis

OBJECTIVEProximal junctional kyphosis (PJK) is, in part, due to altered segmental biomechanics at the junction of rigid instrumented spine and relatively hypermobile non-instrumented adjacent segments. Proper application of posteriorly anchored polyethylene tethers (i.e., optimal configuration and tension) may mitigate adjacent-segment stress and help prevent PJK. The purpose of this study was to investigate the impact of different tether configurations and tensioning (preloading) on junctional range-of-motion (ROM) and other biomechanical indices for PJK in long instrumented spine constructs.METHODSUsing a validated finite element model of a T7–L5 spine segment, testing was performed on intact spine, a multilevel posterior screw-rod construct (PS construct; T11–L5) without tether, and 15 PS constructs with different tether configurations that varied according to 1) proximal tether fixation of upper instrumented vertebra +1 (UIV+1) and/or UIV+2; 2) distal tether fixation to UIV, to UIV−1, or to rods; and 3) use of a loop (single proximal fixation) or weave (UIV and/or UIV+1 fixation in addition to UIV+1 and/or UIV+2 proximal attachment) of the tether. Segmental ROM, intradiscal pressure (IDP), inter- and supraspinous ligament (ISL/SSL) forces, and screw loads were assessed under variable tether preload.RESULTSPS construct junctional ROM increased abruptly from 10% (T11–12) to 99% (T10–11) of baseline. After tethers were grouped by most cranial proximal fixation (UIV+1 vs UIV+2) and use of loop versus weave, UIV+2 Loop and/or Weave most effectively dampened junctional ROM and adjacent-segment stress. Different distal fixation and use of loop versus weave had minimal effect. The mean segmental ROM at T11–12, T10–11, and T9–10, respectively, was 6%, 40%, and 99% for UIV+1 Loop; 6%, 44%, and 99% for UIV+1 Weave; 5%, 23%, and 26% for UIV+2 Loop; and 5%, 24%, and 31% for UIV+2 Weave.Tethers shared loads with posterior ligaments; consequently, increasing tether preload tension reduced ISL/SSL forces, but screw loads increased. Further attenuation of junctional ROM and IDP reversed above approximately 100 N tether preload, suggesting diminished benefit for biomechanical PJK prophylaxis at higher preload tensioning.CONCLUSIONSIn this study, finite element analysis demonstrated UIV+2 Loop and/or Weave tether configurations most effectively mitigated adjacent-segment stress in long instrumented spine constructs. Tether preload dampened ligament forces at the expense of screw loads, and an inflection point (approximately 100 N) was demonstrated above which junctional ROM and IDP worsened (i.e., avoid over-tightening tethers). Results suggest tether configuration and tension influence PJK biomechanics and further clinical research is warranted.

Corrugated Board Flute-Shaped Finite Element Analysis and Optimization

2013 ◽  
Vol 477-478 ◽  
pp. 1205-1209 ◽  
Author(s):  
Wei Yuan ◽  
Gai Mei Zhang ◽  
Da Zhi Liao ◽  
Jing Liu
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Compressive Strength ◽  
Gradual Transition ◽  
Radius Of Curvature ◽  
Element Analysis ◽  
Corrugated Board ◽  
Key Points ◽  
Corrugated Cardboard ◽  
Corrugated Structure

UV-shaped corrugated cardboard Fusion V-shaped and U-shaped structure the advantages made, to make up for the lack of V-type and two U-shaped corrugated cardboard, the higher the compressive strength, good elasticity, is widely used UV type corrugated manufacturing corrugated board. But no strict standards for UV-shaped concrete structure of corrugated board size parameter corresponding corrugating roll no uniform size of the corrugated shape, in order to achieve the best elasticity and compressive strength. First, by mathematical methods, the corrugated structure is analyzed, and analysis to facilitate research, to select the 1/4 cycle corrugated. Create multiple vertical auxiliary line level is divided into 10 equal parts, to identify key points in shape between the V-shaped and U-shaped curve, connecting into multiple segments curve. Studied the actual thickness of the corrugated board of 3.8mm, a smaller thickness and therefore a straight line can be connected to each group of the resultant key points simplify the corrugated curve, model 1/4 of a cycle of UV-shaped corrugated first determined, using the symmetry of the model to establish a cycle, 300mm side length of the square created by one cycle of replication, about 38 of the corrugated board corrugated cycle. Use of finite element analysis in ANSYS corrugated structure, including a gradual transition to a simplified model of the 11 U-shaped flute-shaped corrugated cardboard from the V-shaped set of material properties, loads are cloth pressure, research corrugated cardboard stress and strain, i.e., the smaller the radius of curvature of the curve can be obtained along corrugated, the closer the U-shaped, corrugated board having a larger strain, i.e. has good flexibility, consistent with the empirical data to prove the feasibility of this analysis method.

Modeling Design and Finite Element Analysis of the Hydraulic Gradual Transition

2013 ◽  
Vol 405-408 ◽  
pp. 507-510
Author(s):  
Tao Chen ◽  
Hong Sheng Zhao
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Cross Section ◽  
Practical Significance ◽  
Gradual Transition ◽  
Element Analysis ◽  
Water Load ◽  
Inverted Siphon ◽  
Water Conditions ◽  
Static Water

The inlet and outlet of the aqueduct and the inverted siphon, standing a gradual transition linked to the channel, make water gradually change along the cross section of the gradual transition, to improve the water flow pattern. This paper aims to research the deformation of the gradual transition under the water load in static water conditions, to make ANSYS finite element analysis to the engineering gradual transition for preventing deformation, and finally to optimize the overall style design on the basis of its analysis. The developed techniques have been successfully used in designing the gradual transition of a practical aqueduct project. The results of this study on the gradual transition have strong theoretical and practical significance.

Design factors of lumbar pedicle screws under bending load: A finite element analysis

2019 ◽  
Vol 39 (1) ◽  
pp. 52-62 ◽  
Author(s):  
Jayanta Kumar Biswas ◽  
Tikeshwar Prasad Sahu ◽  
Masud Rana ◽  
Sandipan Roy ◽  
Santanu Kumar Karmakar ◽  
...  
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Pedicle Screws ◽  
Element Analysis ◽  
Bending Load ◽  
Design Factors ◽  
Lumbar Pedicle
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