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Related Concept Videos

Fatigue01:21

Fatigue

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Fatigue occurs when materials rupture under repeated or fluctuating loads, even at stress levels far below their static breaking strength. It typically results in brittle failure, even for ductile materials. It is a critical consideration in designing machines and structural components subjected to repetitive or varying loads. The nature of these loadings can range from fluctuating loads like unbalanced pump impellers causing vibrations to repeatedly bending a thin steel rod wire back and forth...
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Normal Strain under Axial Loading01:20

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Normal strain under axial loading is an important concept in the field of mechanics of materials. Axial loading implies the application of a force along the axis of a material, like a column or bar. This force can either compress or stretch the material. In the context of axial loading, normal strain is the deformation experienced by the material in the direction of the loading force. It's calculated as the change in length divided by the original length of the material. This unitless ratio...
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Machines: Problem Solving I01:22

Machines: Problem Solving I

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A toggle clamp is a mechanical device commonly used for holding and clamping objects in various applications, such as woodworking, metalworking, and assembly operations. Consider a toggle clamp subjected to a force of 200 N at the handle. The vertical clamping force can be calculated, provided the dimensions of the toggle clamp are known.
The toggle clamp system is a machine structure consisting of movable, pin-connected multi-force members that form a stabilized system to transmit forces. The...
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General Case of Eccentric Axial Loading01:12

General Case of Eccentric Axial Loading

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Unsymmetrical bending occurs when the bending moment applied to a structural member does not align with its principal axis. This misalignment leads to complex stress distributions and deflection patterns that differ from symmetrical bending, which are essential for designing structures to withstand different loading conditions.
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Stresses under Combined Loadings01:23

Stresses under Combined Loadings

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When analyzing a bent tube with a circular cross-section subjected to multiple forces, it is crucial to determine the stress distribution in order to maintain structural integrity under varied load conditions.
The process begins by slicing the tube at critical points and analyzing the internal forces and stress components at these sections, focusing on the centroid. Normal stresses, generated by axial forces and bending moments, are either compressive or tensile and vary across the section from...
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Stability of structures01:14

Stability of structures

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In mechanical engineering, the stability of systems under various forces is critical for designing durable and efficient structures. One fundamental way to explore these concepts is by analyzing systems like two rods connected at a pivot point, O, with a torsional spring of spring constant k at the pivot point. This system is similar in appearance to a scissor jack used to change tires on a car. In this case, the arms of the linkage (equivalent to the rods in this system) are entirely vertical,...
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Integrated Fixation Cage Loosening Under Fatigue Loading.

Srinidhi Nagaraja1, Vivek Palepu1

  • 1US Food and Drug Administration, Center for Devices and Radiological Health, Office of Science and Engineering Laboratories, Division of Applied Mechanics, Silver Spring, Maryland, USA.

International Journal of Spine Surgery
|August 3, 2017
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Summary
This summary is machine-generated.

Integrated fixation cages (IFC) show increased screw loosening compared to anterior plate plus cage (AP+C) systems, particularly in medial screws. This finding highlights potential instability in IFC devices under fatigue loading.

Keywords:
anterior platecadaverfatigueimage processingintegrated fixation cagemicro-ctscrew loosening

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Area of Science:

  • Orthopedic surgery
  • Biomedical engineering
  • Spinal biomechanics

Background:

  • Screw loosening is a common complication in spinal fusion, potentially causing instability and non-union.
  • Integrated fixation cages (IFC) offer a low-profile alternative to anterior plate plus cage (AP+C) systems.
  • The screw fixation characteristics of IFCs compared to AP+C implants are not well understood.

Purpose of the Study:

  • To quantitatively compare screw loosening between IFC and AP+C implants under simulated fatigue loading.
  • To investigate the spatial differences in screw fixation for IFC devices.

Main Methods:

  • Human lumbar functional spinal units (FSUs) were instrumented with either IFC or AP+C implants.
  • Specimens underwent simulated fatigue loading (±3 Nm to ±5 Nm) for 20,000 cycles.
  • Micro-computed tomography (micro-CT) was used to assess screw hole volumes post-fatigue, indicating screw loosening.

Main Results:

  • IFC screws exhibited significantly larger screw hole volumes than AP+C screws (p=0.008).
  • Medial IFC screws showed significantly greater loosening than lateral IFC screws and all AP+C screws (p<0.003).
  • No significant difference in loosening was found between lateral IFC screws and AP+C screws.

Conclusions:

  • IFC devices demonstrate a higher propensity for screw loosening compared to AP+C implants.
  • Medial screws in IFCs are particularly susceptible to loosening under fatigue.
  • The micro-CT technique provides a valuable method for evaluating screw fixation in spinal implants.