Tunable Stiffness Bone Rod for Controlled Strain Healing
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Solution Overview
Problem
Existing bone rods for healing long fractured bones have constant stiffness, which does not allow for controlled deformation under axial load, leading to non-uniform bone healing and potential stress-shielding effects that result in osteoporosis.
Innovation Solution
A tunable stiffness bone rod with a stiffness unit comprising upper and lower flex members separated by a gap, connected by a support arm that becomes stiffer as the gap closes under axial load, allowing for controlled deformation and bone healing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bone rod with constant stiffness is used, then the bone fracture can be fixed and rotation prevented, but the strain level cannot be controlled within the optimal range for bone healing
Solution Approach 1:
The bone rod incorporates a tunable stiffness unit with flex members and a gap that allows the rod to transition from a rigid state to a flexible state. Under axial load, the gap closes and flex members deform, enabling the rod to adapt its stiffness dynamically to control strain levels within the optimal 8-10% range for bone healing, while still preventing rotation and maintaining fracture fixation.
2Strength
If metal bone fixators with high stiffness are used, then the bone fracture can be stabilized, but stress-shielding effect occurs leading to osteoporosis
Solution Approach 1:
The invention changes the stiffness parameter of the bone fixator by introducing a tunable stiffness unit with flex members and a controllable gap. This allows the fixator to provide high stiffness for stabilization when needed, while also enabling lower stiffness modes that allow controlled strain transmission to the bone, thereby preventing stress-shielding and associated osteoporosis.
3Adaptability or versatility
If existing flexible bone rods with springs and sliding screws are used, then some flexibility is provided, but the design is not patient-specific and cannot control the amount of strain
Solution Approach 1:
The invention applies local quality by making the bone rod patient-specific through customizable geometry and material properties. The tunable stiffness unit features locally optimized flex members with specific dimensions, thicknesses, and material compositions that can be tailored to each patient's bone characteristics, allowing precise control of strain levels rather than providing generic flexibility.
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 tunable stiffness bone rod promotes controlled and uniform bone healing by allowing deformation within a specific strain range (8-10%), reducing the risk of osteoporosis and stress-shielding effects.
Implementation Method 1
the upper and lower flex members movable to contact one another under axial load
Implementation Method 2
the stiffness unit comprising a stiffness block comprising an upper flex member and a lower flex member separated by a gap, and a support arm connected to the upper and lower flex members, wherein said upper and lower flex members movable to contact one another under axial load
Data Source
AI summary
A tunable stiffness bone rod promotes the healing of fractured bones, such as tibia bones. The tunable stiffness bone rod includes a hexagonal shape that has variable levels of stiffness upon application of an axial force. The axial force will begin a low stiffness movement of the bone rod until a threshold is met. Upon reaching the threshold, the stiffness of the bone rod increases to lessen additional longitudinal movement caused by the axial force on the bone rod.