scholarly journals Influence of pedicle screw thread width and recovery time after surgery on fixation strength

2021 ◽  
Vol 7 (2) ◽  
pp. 751-754
Author(s):  
Harikrishna Makaram ◽  
Ramakrishnan Swaminathan
Keyword(s):  
Cortical Bone ◽  
Pedicle Screw ◽  
Stress Shielding ◽  
Stress Transfer ◽  
Fixation Strength ◽  
Screw Thread ◽  
Fe Model ◽  
Contact Conditions ◽  
Transfer Parameter ◽  
Pull Out

Abstract Introduction: Pedicle screw fixation systems are widely used for treatment of various spinal pathologies, including spinal stenosis, scoliosis, spinal deformities and fractures. Stress shielding is considered to be a major factor contributing to insufficient fixation strength, leading to screw loosening. In this study, the influence of pedicle screw thread width on the displacement of pedicle screw and stress transfer is analyzed using 2-Dimensional axisymmetric finite element (FE) model. Methods: FE model consisting of cancellous and cortical bone, along with pedicle screw is developed for this study. The pedicle screw thread width is varied between 0.1 mm and 0.6 mm in steps of 0.1 mm, while the other geometric parameters, including screw half-angle, pitch, diameter, and length are kept constant. Three different contact conditions between screw and bone, such as frictionless, frictional, and bonded are considered to simulate hours, days, and months after surgery, respectively. The material properties and boundary conditions are applied based on previous studies. An axial force of 80 N is applied on the screw head to simulate axial pull-out test. Results: Similar patterns of stress distribution are observed for all screw models, with high stress concentration above the first thread. The highest displacement in screw is observed shortly after surgery, while the highest displacement in cancellous and cortical bone is observed few days and months after the surgery, respectively. The average von Mises stress in screw decreases with increase in thread width for all contact conditions. In few hours/days after the surgery, stress transfer parameter increases with increase in thread width, up to a thread width of 0.5 mm and then decreases. The changes in stress transfer parameter are negligible few months after the surgery. Conclusion: This study highlights the influence of thread width on displacement and stress transferred to the bone, at different durations after the surgery. It is observed that a thread width of 0.5 mm exhibits the highest stress transfer, leading to reduced stress shielding and improved bone remodeling. It appears that this study might aid in developing better pedicle screws for the treatment of various spinal pathologies.

scholarly journals ANALYSIS ON THE EFFECT OF HALF ANGLE ON THE DISPLACEMENT OF PEDICLE SCREW DURING AXIAL PULL-OUT TEST IN CANCELLOUS BONE USING 2D AXISYMMETRIC FE MODEL

2021 ◽  
Vol 57 (2) ◽  
pp. 153-158
Author(s):  
Harikrishna Makaram ◽  
◽  
Ramakrishnan Swaminathan ◽  
Keyword(s):  
Pedicle Screw ◽  
High Stress ◽  
Pedicle Screws ◽  
Stress Transfer ◽  
Von Mises Stress ◽  
Fe Model ◽  
Distal Half ◽  
Proximal Half ◽  
Pull Out ◽  
Half Angle

Pedicle screw fixations are commonly used in the treatment of spinal pathologies. For effective treatment, stable anchorage between the screw and bone is necessary. In this study, the influence of proximal and distal half angle of the screw, on the displacement of fixation and stress transfer are simulated using a 2D axisymmetric finite element model. A parametric study was performed by varying the proximal half-angle between 0° and 60° in steps of 10° and the distal half angles are considered as 30° and 40°. The material properties and boundary conditions are applied based on previous studies. Frictional contact is considered between the bone and screw. Results show that, displacement of fixation is observed to be minimum at a proximal half angle of 0° and maximum at an angle of 60°. High stress concentration is observed in first few threads with highest maximum von Mises stress at an angle of 60°. High stress transfer was obtained for proximal half-angles of 40° and 50°. It is observed that, this method might aid to develop better pedicle screws for treatment of Scoliosis.

Comparison of Three Different Screw Trajectories in Osteoporotic Vertebrae: A Biomechanical Investigation

2020 ◽  
Author(s):  
Jan-Sven Jarvers ◽  
Stefan Schleifenbaum ◽  
Christian Pfeifle ◽  
Christoph Oefner ◽  
Melanie Edel ◽  
...  
Keyword(s):  
Cortical Bone ◽  
Fatigue Behavior ◽  
Fixation Strength ◽  
Patient Specific ◽  
Promising Alternative ◽  
Cortical Bone Trajectory ◽  
Pull Out ◽  
Group A ◽  
The Mean ◽  
Group B

Abstract Background: Pedicle screw insertion in osteoporotic patients is challenging. Achieving more screw-cortical bone purchase and invasiveness minimization, the cortical bone trajectory and the midline cortical techniques represent alternatives to traditional pedicle screws. This study compares the fatigue behavior and fixation strength of the cement-augmented traditional trajectory (TT), the cortical bone trajectory (CBT) and the midline cortical (MC). Methods: Ten human cadaveric spine specimens (L1 - L5) were examined. The average age was 86.3 ± 7.2 years. CT scans were provided for preoperative planning. CBT and MC were implanted by using the patient-specific 3D-printed placement guide (MySpine®, Medacta International), TT were implanted freehand. All 10 cadaveric specimens were randomized to group A (CBT vs. MC) or group B (MC vs. TT). Each screw was loaded for 10,000 cycles. The failure criterion was doubling of the initial screw displacement resulting from the compressive force (60 N) at the first cycle, the stop criterion as a doubling of the initial screw displacement. After dynamic testing, screws were pulled out axially at 5 mm/min to determine their remaining fixation strength. Results: The mean pull-out forces did not differ significantly. Concerning the fatigue performance, only one out of ten MC of group A failed prematurely due to loosening after 1,500 cycles (L3). Five CBT already loosened during the first 500 cycles. The mean displacement was always lower in the MC. In group B, all TT showed no signs of failure or loosening. Three MC failed already after 26 cycles, 1,510 cycles, and 2,144 cycles, respectively. The TT showed always a lower mean displacement. In the subsequent pull-out tests, the remaining mean fixation strength of the MC (449.6 ± 298.9 N) was slightly higher compared to the mean pull-out force of the CBT (401.2 ± 261.4 N). However, MC (714.5 ± 488.0 N) were inferior to TT (990.2 ± 451.9 N).Conclusion: The current study demonstrated that cement-augmented TT have best fatigue and pull-out characteristics in osteoporotic lumbar vertebrae, followed by the MC and CBT. MC represent a promising alternative in osteoporotic bone if cement augmentation should be avoided. Using the patient-specific guide contributes to improve screws’ biomechanical properties.

scholarly journals Balancing Rigidity and Safety of Pedicle Screw Fixation via a Novel Expansion Mechanism in a Severely Osteoporotic Model

2015 ◽  
Vol 2015 ◽  
pp. 1-11 ◽  
Author(s):  
Thomas M. Shea ◽  
James J. Doulgeris ◽  
Sabrina A. Gonzalez-Blohm ◽  
William E. Lee ◽  
Kamran Aghayev ◽  
...  
Keyword(s):  
Cortical Bone ◽  
Pedicle Screw ◽  
Pedicle Screws ◽  
Pedicle Screw Fixation ◽  
Cortical Layer ◽  
Fixation Strength ◽  
Osteoporotic Bone ◽  
Pullout Strength ◽  
Initial Fixation ◽  
Increased Risk

Many successful attempts to increase pullout strength of pedicle screws in osteoporotic bone have been accompanied with an increased risk of catastrophic damage to the patient. To avoid this, a single-armed expansive pedicle screw was designed to increase fixation strength while controlling postfailure damage away from the nerves surrounding the pedicle. The screw was then subsequently tested in two severely osteoporotic models: one representing trabecular bone (with and without the presence of polymethylmethacrylate) and the other representing a combination of trabecular and cortical bone. Maximum pullout strength, stiffness, energy to failure, energy to removal, and size of the resulting block damage were statistically compared among conditions. While expandable pedicle screws produced maximum pullout forces less than or comparable to standard screws, they required a higher amount of energy to be fully removed from both models. Furthermore, damage to the cortical layer in the composite test blocks was smaller in all measured directions for tests involving expandable pedicle screws than those involving standard pedicle screws. This indicates that while initial fixation may not differ in the presence of cortical bone, the expandable pedicle screw offers an increased level of postfailure stability and safety to patients awaiting revision surgery.

scholarly journals A biomechanical study of a novel biomimetic hip implant.

2021 ◽  
Author(s):  
Shaheen Khurshid
Keyword(s):  
Three Dimensional ◽  
Stress Shielding ◽  
Stress Transfer ◽  
Biomechanical Study ◽  
Von Mises Stress ◽  
Fe Model ◽  
Polyamide 12 ◽  
Hip Stems ◽  
Von Mises ◽  
Three Dimensional Finite Element

A three dimensional finite element (FE) model of a novel carbon fibre polyamide 12 composite hip stem was used to compare with two commerically available (Exeter and Omnifit) hip stems to minimize stress shielding and bone resorption. A virtual axial load of 3000N was applied to the FE model which replicated the experimental study. Strain and stress distributions were computed and compared with experimental results. Experimentally, three hip stems had their distal portions rigidly mounted and had strain gauges placed along the surface at 3 medial and 3 lateral locations. From the FE analysis, the von mises stress range for the composite hip stem was 200% and 45% lower than that in the Omnifit and Exeter implants, respectively. The aggregate average difference between FE and experimental microstrains for four proximal strain gauge locations were 7.5% (composite), 11.5% (Exeter), 14.6% (Omnifit), and the composite hip stem's stiffness (1982N/mm) was lower than the metallic hip stem stiffnesses (Exter, 2460N/mm; Omnifit, 2543 N/mm). This study showed considerable improvement in stress transfer to bone tissue.

scholarly journals A biomechanical study of a novel biomimetic hip implant.

2021 ◽  
Author(s):  
Shaheen Khurshid
Keyword(s):  
Three Dimensional ◽  
Stress Shielding ◽  
Stress Transfer ◽  
Biomechanical Study ◽  
Von Mises Stress ◽  
Fe Model ◽  
Polyamide 12 ◽  
Hip Stems ◽  
Von Mises ◽  
Three Dimensional Finite Element

A three dimensional finite element (FE) model of a novel carbon fibre polyamide 12 composite hip stem was used to compare with two commerically available (Exeter and Omnifit) hip stems to minimize stress shielding and bone resorption. A virtual axial load of 3000N was applied to the FE model which replicated the experimental study. Strain and stress distributions were computed and compared with experimental results. Experimentally, three hip stems had their distal portions rigidly mounted and had strain gauges placed along the surface at 3 medial and 3 lateral locations. From the FE analysis, the von mises stress range for the composite hip stem was 200% and 45% lower than that in the Omnifit and Exeter implants, respectively. The aggregate average difference between FE and experimental microstrains for four proximal strain gauge locations were 7.5% (composite), 11.5% (Exeter), 14.6% (Omnifit), and the composite hip stem's stiffness (1982N/mm) was lower than the metallic hip stem stiffnesses (Exter, 2460N/mm; Omnifit, 2543 N/mm). This study showed considerable improvement in stress transfer to bone tissue.

scholarly journals The effect of cement augmentation on pedicle screw fixation under various load cases

2021 ◽  
Vol 10 (12) ◽  
pp. 797-806
Author(s):  
Yan Chevalier ◽  
Maiko Matsuura ◽  
Sven Krüger ◽  
Hannes Traxler ◽  
Christoph Fleege† ◽  
...  
Keyword(s):  
Pedicle Screw ◽  
Bone Quality ◽  
Pedicle Screws ◽  
Bending Stiffness ◽  
Cement Augmentation ◽  
Fixation Strength ◽  
Screw Design ◽  
Pull Out ◽  
Local Bone ◽  
Significant Difference

Aims Anchorage of pedicle screw rod instrumentation in the elderly spine with poor bone quality remains challenging. Our study aims to evaluate how the screw bone anchorage is affected by screw design, bone quality, loading conditions, and cementing techniques. Methods Micro-finite element (µFE) models were created from micro-CT (μCT) scans of vertebrae implanted with two types of pedicle screws (L: Ennovate and R: S4). Simulations were conducted for a 10 mm radius region of interest (ROI) around each screw and for a full vertebra (FV) where different cementing scenarios were simulated around the screw tips. Stiffness was calculated in pull-out and anterior bending loads. Results Experimental pull-out strengths were excellently correlated to the µFE pull-out stiffness of the ROI (R2 > 0.87) and FV (R2 > 0.84) models. No significant difference due to screw design was observed. Cement augmentation increased pull-out stiffness by up to 94% and 48% for L and R screws, respectively, but only increased bending stiffness by up to 6.9% and 1.5%, respectively. Cementing involving only one screw tip resulted in lower stiffness increases in all tested screw designs and loading cases. The stiffening effect of cement augmentation on pull-out and bending stiffness was strongly and negatively correlated to local bone density around the screw (correlation coefficient ( R) = -0.95). Conclusion This combined experimental, µCT and µFE study showed that regional analyses may be sufficient to predict fixation strength in pull-out and that full analyses could show that cement augmentation around pedicle screws increased fixation stiffness in both pull-out and bending, especially for low-density bone. Cite this article: Bone Joint Res 2021;10(12):797–806.

Comparison of Surgical Outcomes between Cortical Bone Trajectory and Conventional Pedicle Screw Trajectory for Lumbar Degenerative Spondylolisthesis (systematic review of literature)

QJM ◽  
2021 ◽  
Vol 114 (Supplement_1) ◽  
Author(s):  
Mohamed Fawzy Khattab ◽  
Mostafa Atef Kamal ◽  
Mbbch Naser Hussein Zaher
Keyword(s):  
Cortical Bone ◽  
Pedicle Screw ◽  
Clinical Outcomes ◽  
Sagittal Plane ◽  
Degenerative Spondylolisthesis ◽  
Leg Pain ◽  
Fixation Strength ◽  
Cortical Bone Trajectory ◽  
Non Union ◽  
Spine Stabilization

Abstract Background Pedicle screw fixation the gold standard for lumbar spine stabilization. Pedicle screw has fixation offers multiple advantages, allowing superior correction of spinal deformities, and reduced rates of loss of non-union. Cortical Bone Trajectory (CBT) is a new technique in which screws follow a caudal-to-cephalad path in the sagittal plane and a medial-to-lateral directed path in the transverse plane. CBT is reducing operative and post-operative complications and has high fixation strength. Purpose To Compare the clinical outcomes between CBT and traditional trajectory (TT) in surgical management of degenerative spondylolisthesis. Materials and Methods A comprehensive electronic search in Pubmed, MEDLINE and Chocrane library databases, Google scholar and Research gate for articles that published between 2009 to 2020 using these keywords: Cortical bone trajectory, Cortical bone trajectory-pedicle screw, Pedicle screw. Results The majority of literature suggests that the CBT technique results in similar or decreased postoperative back and leg pain compared to TT. Regarding the disability ODI and the operative time showed no significant differences between the CBT and TT. Radiographic outcomes between both studies show no statistical difference in fusion rates and vertebral slippage. Intraoperative blood loss was significantly less with CBT compared to TT. Conclusion there is no widely accepted consensus regarding comparison of clinical outcomes and complications between the CBT and TT procedures. Generally, indications for CBT and TT are similar between most studies, especially for common pathologies resulting in spondylolisthesis.

scholarly journals Design and Structural Analysis of a Rack System for Using in Agriculture

2018 ◽  
Vol 66 (3) ◽  
pp. 641-646
Author(s):  
Miroslav Blatnický ◽  
Ján Dižo ◽  
Dalibor Barta
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Structural Analysis ◽  
Fe Model ◽  
Steel Tubes ◽  
Shell Elements ◽  
Human Power ◽  
Construction Design ◽  
Pull Out ◽  
Pressure Pipeline

The paper deals with a construction design and structural analysis of the rack system which will be used for storage of steel tubes of pressure pipeline for fodder mixtures transportation in agricultural company. Structure of the designed equipment is made by the welding of steel parts and consists of the main framework and four pull-out racks on both sides. Racks move by means of human power through a rotating crank. Every individual pull-out racks is able to carries pipes of various dimensions, both length and diameter with total weight up to 3 tons with respect to customer requests. Since it is a prototype’s structure, we have designed main dimensions of it, material and technology for production and performed also structural analyses as the integral part of every engineering design. Structural analyses were conducted by means of numeric procedure known as finite element method. With respect to the used steel profiles shell elements were used for FE model. Analyses were performed for maximal loading cases in order to identify the level of safety in the most exposed locations of the structure.

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