Variable Stiffness Spinal Rod for Adjacent Level Stress Reduction
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Solution Overview
Problem
Current spinal fixation devices often lead to proximal junctional kyphosis (PJK) and adjacent level failure due to inadequate restoration of spinal stiffness and structural support, resulting in post-surgical morbidity and the need for additional surgeries.
Innovation Solution
A spinal fixation member with varying stiffness properties along its length, comprising a core member and a sheath member made of different materials and shapes, where the core member has a uniform diameter and the sheath member has a tapered or smaller diameter portion to reduce stiffness at specific ends, allowing for a transition from a stiffer instrumented spine to a less stiff non-instrumented spine.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a uniform stiffness spinal rod is used throughout its length, then the spinal column provides adequate structural support and stability, but it causes excessive stress on adjacent levels and leads to proximal junctional kyphosis (PJK)
Solution Approach 1:
The spinal rod is designed with varying stiffness properties along its length, with a first portion having a first stiffness and a second portion having a second stiffness different from the first. This allows the rod to provide stronger support where needed while reducing stress on adjacent levels, directly resolving the contradiction between providing adequate structural support and minimizing harmful stress on adjacent vertebrae.
Solution Approach 2:
The patent changes the physical parameter of stiffness along the length of the spinal rod. By varying the modulus of elasticity, cross-sectional area, or wall thickness at different portions of the rod, it creates a gradient of stiffness that transitions from a stiffer instrumented spine to a more flexible non-instrumented spine, reducing the abrupt transition that causes PJK.
2Stability of the object's composition
If a stiffer spinal rod is used to maintain spinal alignment, then sagittal balance is improved, but facet capsule and muscle disruption increases
Solution Approach 1:
The spinal rod has different stiffness characteristics at different portions, allowing it to maintain sagittal balance through the stiffer first portion while the second portion with reduced stiffness minimizes disruption to facet capsules and muscles at the junctional level.
Solution Approach 2:
The varying stiffness design allows the spinal rod to dynamically adapt to the mechanical requirements of different spinal regions, providing rigidity where alignment is critical and flexibility where soft tissue preservation is important.
Data Source
AI summary
A system for fixing spinal vertebrae utilizes a spinal rod that has varying properties along its length such that a lower stiffness portion is placed in the cranial or caudal end positions of the spinal rod to address potential adjacent level failure. The spinal rod includes a core member formed of a first material having a first modulus of elasticity and a sheath member formed of a second material having a second modulus of elasticity different from the first modulus of elasticity. The core member includes a first portion having a uniform outer diameter and a second portion extending from the first portion. At least a portion of the second portion has an outer diameter smaller than the uniform outer diameter of the first portion. The sheath member has a lumen extending therethrough that is sized for slidably receiving the second portion of the core member therein.