Intervertebral Fusion Cage With Opposing Serrations for Subsidence Control
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Solution Overview
Problem
Existing intervertebral fusion cages face issues such as subsidence, inadequate lordosis restoration, difficulty in reducing spondylolisthesis, cage migration, and safety concerns during placement, leading to potential nerve damage and non-union.
Innovation Solution
The intervertebral fusion cage features a body with opposing serrations on its top and bottom surfaces to grip the vertebrae endplates, complemental engagement formations for secure placement, and a central pillar for support, along with insertion instrumentation using blades and a drive tool to minimize movement and ensure accurate positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the cage rests on the cancellous endplate, then the cage can be inserted easily, but subsidence occurs due to the softer bone material
Solution Approach 1:
The cage incorporates gripping formations (protrusions or rough surfaces) at specific contact points on its superior and inferior surfaces to engage with the cortical rim of the vertebral endplates. This localized enhancement of surface properties allows the cage to rest on the stronger cortical bone rather than the softer cancellous bone, preventing subsidence while maintaining ease of insertion.
2Volume of moving object
If the cage surface area is small, then the cage size is reduced for minimal invasion, but force concentration increases leading to endplate fracture
Solution Approach 1:
The cage distributes its weight through gripping formations that concentrate contact forces at specific engagement points on the cortical rim, rather than spreading pressure over a large surface area. This allows a compact cage design to achieve stable support without requiring extensive surface area, thus maintaining minimal invasiveness while preventing endplate fracture.
3Strength
If the cage material has high strength, then the cage can support vertebral loads, but the modulus of elasticity differs significantly from bone causing stress shielding
Solution Approach 1:
The cage is designed with a modular structure where the main body can be made of high-strength material (titanium or PEEK) to support vertebral loads, while the gripping formations are specifically engineered with surface properties that promote bone ingrowth and mechanical interlocking. This parameter optimization allows the cage to provide necessary structural support while facilitating fusion through controlled stress transfer at the bone-cage interface.
4Reliability
If the cage is designed to engage the cortical rim, then subsidence is prevented, but insertion precision requirements increase
Solution Approach 1:
The cage incorporates engagement formations (such as ledges or complementary shaped surfaces) that are designed to automatically align with and engage the cortical rim of the vertebral endplates upon insertion. This preliminary geometric configuration guides the cage into the correct position during insertion, reducing the precision requirements for the surgical procedure while ensuring stable cortical rim engagement.
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 first direction while the gripping formations on the bottom surface obstruct movement in a second direction, which is substantially opposite the first direction.