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Related Concept Videos

Net Torque Calculations01:19

Net Torque Calculations

When a mechanic tries to remove a hex nut with a wrench, it is easier if the force is applied at the farthest end of the wrench handle. The lever arm is the distance from the pivot point (the hex nut in this case) to the person’s hand. If this distance is large, the torque is higher. Only the component of the force perpendicular to the lever arm contributes to the torque. Therefore, pushing the wrench perpendicular to the lever arm is more advantageous. If multiple people apply force to rotate...
Screw: Problem Solving01:21

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Torque01:10

Torque

Torque is an important quantity for describing the dynamics of a rotating rigid body. We see the application of torque in many ways in the world, such as when pressing the accelerator in a car, which causes the engine to apply additional torque on the drivetrain. Here, we define torque and provide a framework to create an equation to calculate torque for a rigid body with fixed-axis rotation.
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Circular Shafts - Elastoplastic Materials01:24

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The study of solid circular shafts under stress shows that within the elastic limit, stress increases directly to the distance from the shaft's center. This relationship holds until the shaft reaches a critical point of stress, beyond which it begins to yield, marking the transition from elastic to plastic deformation. At this crucial juncture, the maximum torque the shaft can endure without permanent deformation is determined, signifying the limit of its elastic behavior.
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Frictional Forces on Screws01:17

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Magnetic Tweezers for the Measurement of Twist and Torque
11:41

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Does maximum torque mean optimal pullout strength of screws?

Sara E Tankard1, Simon C Mears, Daniel Marsland

  • 1International Center for Orthopaedic Advancement, Department of Orthopaedic Surgery, The Johns Hopkins University, Baltimore, MD 21224-2780, USA.

Journal of Orthopaedic Trauma
|November 2, 2012
PubMed
Summary

Tightening cortical screws beyond 50% maximum insertion torque does not improve pullout strength and may risk bone damage. The study found no clear relationship between screw torque and fixation strength in cadaveric humeri.

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Area of Science:

  • Orthopedic surgery
  • Biomechanical engineering
  • Bone research

Background:

  • Cortical screw fixation is crucial in orthopedic surgery.
  • Understanding the relationship between insertion torque and screw pullout strength is vital for optimal fixation.
  • Bone mineral density (BMD) variations may influence screw fixation efficacy.

Purpose of the Study:

  • To investigate the correlation between insertion torque and pullout strength of 3.5-mm cortical screws.
  • To assess this relationship across different bone mineral densities (BMDs) in cadaveric humeri.
  • To determine if exceeding a certain insertion torque threshold enhances screw fixation.

Main Methods:

  • Utilized cadaveric humeri from normal, osteopenic, and osteoporotic BMD groups.
  • Measured maximum insertion torque (Tmax) for screws, then tightened them to 50%, 70%, or 90% of Tmax.
  • Assessed screw pullout strength using a servohydraulic testing machine, analyzing data with a mixed-effects model accounting for cortical thickness and BMD.

Main Results:

  • For normal and osteoporotic bone, 50% Tmax insertion yielded the greatest pullout strength.
  • Osteopenic bone showed greatest pullout strength at 70% Tmax, with no significant differences across tested torque levels.
  • Pullout strength did not consistently increase with higher insertion torque percentages across all BMD groups.

Conclusions:

  • Exceeding 50% Tmax for screw insertion does not enhance pullout strength and may compromise bone integrity.
  • Higher insertion torque does not guarantee improved screw fixation and could lead to bone damage.
  • No definitive relationship was established between insertion torque and screw pullout strength, even after controlling for bone characteristics.