Superelastic Bone Screw for Mobile Joint Fixation
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Solution Overview
Problem
Conventional screws and plates used for stabilizing fractured bones or torn joints at highly mobile joints, such as syndesmosis and Lisfranc joints, often fail due to shear forces, and button suture devices may creep over time.
Innovation Solution
The use of screws made from superelastic materials, such as nitinol alloys, which can accommodate shear forces and maintain stability at these joints, along with targeting guides, drill bits, and bone plates for precise fixation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional rigid screws and plates are used to stabilize bones at highly mobile joints, then initial fixation strength is improved, but implant failure occurs due to shear forces at mobile joints
Solution Approach 1:
The patent changes the material parameter from rigid conventional metals to superelastic nitinol alloy, which exhibits non-linear stress-strain behavior. This allows the screw to deform elastically under shear forces and return to its original shape, accommodating joint movement while maintaining fixation strength and preventing implant failure.
Solution Approach 2:
The patent employs a composite material approach by using nitinol alloy that combines the strength of metal with superelastic properties. This composite material behavior enables the screw to simultaneously provide rigid fixation when needed and flexible deformation to accommodate shear forces at mobile joints, resolving the contradiction between initial strength and long-term reliability.
2Adaptability or versatility
If button suture devices are used to accommodate shear forces at syndesmosis joints, then flexibility is improved, but creep occurs over time leading to fixation failure
Solution Approach 1:
The patent changes the material parameter from sutures to superelastic nitinol alloy screws. The nitinol material exhibits strain recovery properties that prevent permanent deformation (creep) while maintaining flexibility to accommodate shear forces. This resolves the contradiction by providing both adaptability to joint movement and long-term fixation durability.
3Stability of the object's composition
If highly rigid fixation devices are used at mobile joints, then initial stability is improved, but shear forces cause implant failure
Solution Approach 1:
The patent applies dynamics by using a material that transitions from rigid to flexible and back to rigid dynamically. The superelastic nitinol screw remains rigid during normal function to maintain stability but deforms elastically when subjected to shear forces from joint movement, then returns to its original rigid state. This dynamic behavior resolves the contradiction between initial stability and long-term reliability at mobile joints.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The superelastic screws effectively reduce the risk of implant failure at highly mobile joints by accommodating shear forces, while maintaining stability and reducing the likelihood of creep in button suture devices.
Implementation Method 1
at least one screw comprising a superelastic material
Data Source
AI summary
A syndesmotic or Lisfranc fixation system can include at least one screw including superelastic material. A syndesmotic fixation method can include screwing a screw including super elastic material through a tibia and a fibula at a syndesmosis joint. A Lisfranc fixation method can include screwing a screw including superelastic material through at least two bones, where a Lisfranc joint complex includes the at least two bones.