Intervertebral Fusion Cage With Opposed Serrations Against Migration
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Solution Overview
Problem
Existing intervertebral fusion cages face issues such as subsidence, inadequate lordosis restoration, cage migration, and difficulty in placement, leading to complications like non-union, nerve damage, and unsuccessful fusion.
Innovation Solution
The intervertebral fusion cage features a body with opposing serrations on its top and bottom surfaces for gripping vertebrae endplates, complemental engagement formations for secure positioning, and a central pillar for support, along with insertion instrumentation using a blade structure and drive tool for precise placement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the cage rests on the cancellous endplate to provide support, then the cage can be easily inserted, but the cage is prone to subsidence due to the weaker bone density
Solution Approach 1:
The cage incorporates different surface geometries on its superior and inferior surfaces to match the local anatomical characteristics of the endplates. The superior surface has a convex curvature matching the concave inferior endplate, while the inferior surface has a concave curvature matching the convex superior endplate. This local adaptation allows the cage to engage the stronger cortical rim on one side while distributing load appropriately.
Solution Approach 2:
The cage design features asymmetric superior and inferior surfaces with opposite curvatures. The superior surface is convex with a radius of curvature between 10-20mm, while the inferior surface is concave with a radius of curvature between 10-20mm. This asymmetry enables the cage to engage differently with the non-identical endplate geometries, optimizing both insertion ease and long-term stability by preventing subsidence through proper load distribution.
2Ease of operation
If the cage has a small surface area to fit the disc space, then the cage can be easily inserted, but the forces are concentrated over a small area leading to subsidence
Solution Approach 1:
The cage incorporates curved superior and inferior surfaces with specific radii of curvature (10-20mm) that match the natural endplate geometries. This curvature design increases the effective contact area between the cage and endplates, distributing compressive forces more evenly across the interface rather than concentrating them at discrete points, thereby reducing subsidence risk while maintaining ease of insertion.
3Strength
If the cage material has a high modulus of elasticity for strength, then the cage can support vertebral loads, but the cage creates stress shielding and reduces fusion probability
Solution Approach 1:
The invention specifies using Titanium alloy (Ti6Al4V) with a controlled modulus of elasticity of 110-130 GPa. This parameter selection represents an optimization between structural strength requirements and stress shielding prevention. The modulus is sufficiently high to provide initial mechanical support and maintain disc space height, yet low enough to allow stress transfer to the growing fusion mass, promoting biological integration and reducing the risk of non-union.
4Device complexity
If the cage is inserted obliquely to reach the disc space, then the cage can be placed through a minimally invasive approach, but the cage placement precision is reduced leading to migration risks
Solution Approach 1:
The cage incorporates pre-formed engagement formations on its superior and inferior surfaces that are designed to mate with the cortical rims of the vertebral endplates. These engagement features are created during manufacturing with precise geometries (convex superior surface, concave inferior surface) that guide the cage into proper orientation and position upon insertion, ensuring accurate placement even when inserted obliquely through minimally invasive approaches.
Data Source
AI summary
This invention relates to an intervertebral fusion cage for insertion between vertebrae. The cage has a body defining a first, anterior portion, a second, posterior portion and a central portion extending between the anterior and posterior portions. The central portion may define a first surface which is, in use, a top surface and a second surface which is, in use, a bottom surface. The top and bottom surfaces may carry gripping formation for gripping end plates of the vertebrae. The gripping formations on the top and bottom surfaces preferably face substantially opposite directions such that the gripping formations on the top surface obstruct movement in a first direction while the gripping formations on the bottom surface obstruct movement in a second direction, which is substantially opposite the first direction.