Rotational Offset Oval Vertebral Rod for Spinal Stabilization
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Solution Overview
Problem
Current spinal stabilization devices fail to provide dynamic stabilizing resistance while allowing motion of spinal column segments, and they often do not effectively reduce stress on spinal elements during treatment of disorders like degenerative disc disease and kyphosis.
Innovation Solution
A flexible vertebral rod with varying stiffness, featuring an oval or non-oval shape at one end and a transition portion with median stiffness, allowing for rotational offset and surface treatments like osteointegrating coatings, to provide stability and reduce stress on spinal elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a rigid vertebral rod is used to provide stability, then structural strength is improved, but stress on spinal elements increases and motion is restricted
Solution Approach 1:
The vertebral rod incorporates different stiffness regions along its length, with the first end portion having higher stiffness for fusion resistance and the second end portion having lower stiffness to reduce stress on spinal elements. This local variation in mechanical properties allows the rod to provide stability where needed while reducing harmful stresses elsewhere.
Solution Approach 2:
The rod's cross-sectional geometry is varied along its length, with the first end portion having a larger cross-sectional area than the second end portion. This parameter change creates a gradient in stiffness that balances structural strength with stress reduction, allowing the rod to adapt its mechanical response to different spinal regions.
2Ease of operation
If a flexible connecting element is used to permit spinal motion, then dynamic support is improved, but stabilizing resistance is reduced
Solution Approach 1:
The rod provides different levels of flexibility at different locations: the first end portion with higher stiffness provides stabilizing resistance for fusion, while the second end portion with lower stiffness permits controlled spinal motion. This local differentiation allows the single rod structure to simultaneously provide both stabilization and dynamic support.
3Strength
If the rod cross-sectional area is increased to enhance strength, then load-bearing capacity is improved, but flexibility is reduced
Solution Approach 1:
The rod is segmented into distinct regions with different cross-sectional areas: a first end portion with a larger cross-sectional area for enhanced load-bearing capacity and stability, and a second end portion with a smaller cross-sectional area for increased flexibility. This segmentation allows each region to optimize its mechanical properties for its specific function.
Data Source
AI summary
A flexible connection unit for use in a spinal fixation device is provided. The flexible connection unit includes an elongated member, such as a vertebral rod, having a first end portion and a second end portion opposite each other with a transition portion extending therebetween. The first end portion of the vertebral rod comprises an oval shape and the second end portion contains an oval or non-oval shape. The major diameter of the oval shaped first end is parallel to the sagittal plane of a patient's body and provides the higher stiffness for fusion to resist flexion in the sagittal plane. The second end portion of the vertebral rod is perpendicular to the sagittal end of a patient's body and provides the lower stiffness for fusion.