Analysis of stress induced by screws in the vertebral fixation system

Lee

et al. 2018

Sci Rep

A polymer coating as polycaprolactone (PCL) is applied to improve the initial corrosion resistance of biodegradable magnesium. In addition, plasma electrolytic oxidation (PEO) is performed to increase adhesion between the polymer and the metal. However, when a complex-shaped material such as a screw is implanted in a bone, the surface coatings are locally damaged, and the protective role of the coating is not sufficiently maintained. In this study, the optimal conditions for producing a polymer coating on a screw were determined by varying the concentration of the PCL and the coating cycles, and were examined in vitro and in vivo. Among various the PCL coating conditions of 2∼6 cycles with 5∼7 wt.% concentrations, the 6 wt.% + 4 cycles group was applied uniformly to the screw thread. In the case of the non-uniform PCL layers, oxides and gases were present between the Mg and the PCL layer because internal magnesium corrosion and the layer peel off. The 6 wt.% + 4 cycles group had a high corrosion resistance due to the low wear on the thread. Denser and thicker bone formed around the PCL-coated screw in rat femur. This difference was due to the high corrosion resistance, which provided sufficient time for bone healing and promoting new bone growth.

Section: Discussionmentioning

confidence: 97%

Improvement of osteogenesis by a uniform PCL coating on a magnesium screw for biodegradable applications

Lee

et al. 2018

Sci Rep

“…The results showed that the screw-vertebra interface stresses in the IFC model were obviously lower than those of the ACPC models in flexion-extension and lateral bending, and higher during rotation. It can thus be concluded that IFC can effectively reduce the risk of screw loosening in most motion conditions [28], and as such, IFC may provide an option to reduce screw-related complications.…”

Section: Discussionmentioning

confidence: 99%

Biomechanical Comparison of Integrated Fixation Cage Versus Anterior Cervical Plate and Cage in Anterior Cervical Corpectomy and Fusion (ACCF): A Finite Element Analysis

Ouyang

Teng

et al. 2019

Med Sci Monit

Background Anterior cervical plate and cage fixation system (ACPC) used in anterior cervical corpectomy and fusion (ACCF) is reported to incur excess complications. This study aimed to introduce integrated fixation cage (IFC) into ACCF to eliminate the anterior cervical plate (ACP)-related complications. Material/Methods One validated intact and 3 ACCF-simulated C3–C7 cervical spine models were developed. In ACCF models, C5 was corpectomied and fixed by IFC or ACPC. For each model, 1.0 Nm moments of flexion, extension, lateral bending, and torsion were imposed on the C3 vertebra. The range of motion (ROM) of each segment and the stress distribution on screw-vertebra interface, bone graft, and cage-endplate were recorded and analyzed. Results ROMs of C3–C7 were not different in any motion condition between IFC and ACPC models. The maximal von Mises stress on screw-vertebra interface of the IFC model was lower than that of the ACPC models in flexion, extension, and lateral bending, but higher in rotation. The maximal von Mises stress on bone graft of the IFC model was higher compared with the ACPC models, except in flexion. The IFC model showed a higher maximal von Mises stress on cage-endplate interface in all motion planes. Conclusions Based on finite element analysis, IFC provided identical C3–C7 construct stability as ACPC. Compared with ACPC, IFC showed better biomechanical performance on screw-vertebra interface and bone graft, but worse biomechanical performance on cage-endplate interface.

“…the polyurethane screws. This is due to the presence of localised stresses in a relatively small area of fixation [30]. In terms of average stresses, it can be inferred from table 4 in the standalone femur; it is less than the conventional model; however, the stress is even lower in the proposed design.…”

Section: Total or Equivalent Stressesmentioning

confidence: 86%

“…The values of maximum strain in natural bone and the proposed prosthesis are comparable. However, maximum strain in the conventional design is high, which is expected because of the localized stresses discussed above [30]. Maximum straining occurs at the femoral shaft for each design.…”

Section: Equivalent Strainmentioning

confidence: 94%

Novel Stemless Hip Prosthesis Design and Finite Element Analysis to validate stemless Prosthesis for Reduction of Aseptic Loosening in Total Hip Arthroplasty

Khadka¹,

Yadav²,

Ghimire³

2020

Preprint

Total Hip Arthroplasty/ Replacement is a major corrective procedure involving replacement of femoral head and neck of the long bone connected to the pelvis. Conventional methods involved using long stemmed Titanium Alloy (Ti6Al4V) implants with a Cobalt-Chrome (Co-Cr) spherical caps. The invasiveness, large distributions of interfacial stresses induce stress shielding and bone resorption leading to loosening and painful remission surgeries specifically in the younger more active individuals. The need to improve upon the less invasive stemless models in warranted. This paper incorporates an improved novel design to a stemless hip prosthesis. Finite element analysis concluded average stresses of 9MPa, average strains of 0.0063 mm/mm, total deformation of 88mm all within comparable ranges and better than conventional long-stemmed models as prosthesis for an exaggerated point load of thrice the body weight of human (867N) taken redundantly. Fatigue life is better than conventional models crossing 1010 cycles for the extreme loading. The contact stresses also proved to be lesser and spread over a smaller area reducing the chances of aseptic loosening compared to conventional models.