Staged Expandable Trial for Vertebral Endplate Subsidence
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current systems for distracting intervertebral disc spaces during spinal fusion procedures often result in subsidence of fusion cages into the vertebrae, leading to a narrowing of the disc space due to inadequate distribution of distraction stresses, which is not effectively addressed by existing methods like the Medtronic SCISSOR JACK or oversized trial shims.
Innovation Solution
A staged, bilaterally expandable trial is introduced that first expands laterally and then vertically to distribute distraction stresses across the peripheral zones of the vertebral endplates, reducing subsidence and facilitating a larger footprint for load distribution without contracting in length, thereby improving the stability and size selection of the intervertebral space.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a narrow distraction means (8-11 mm width) is used to insert the fusion cage, then the insertion is minimally invasive, but the distraction stress is concentrated on the central endplate area which is softer, causing subsidence of the cage into the vertebrae
Solution Approach 1:
The distraction system is divided into multiple expandable legs (first leg, second leg, third leg, fourth leg) that can be independently positioned and expanded. Each leg applies distraction stress to different zones of the endplate, segmenting the force distribution to avoid concentration on the soft central area while maintaining minimally invasive insertion through a single narrow annulotomy.
Solution Approach 2:
The distraction legs are designed with different expansion characteristics and contact surfaces to apply force locally to specific endplate zones. The peripheral zones receive higher distraction stress from the expanded legs, while the central soft area is avoided, creating localized quality in force application that prevents subsidence while maintaining insertion ease.
2Ease of manufacture
If the distraction stress is applied to the central endplate area, then the insertion procedure is simplified, but the softer central area causes the cage to sink into the vertebrae creating subsidence
Solution Approach 1:
The distraction legs are pre-positioned and pre-expanded to the desired configuration before the fusion cage is inserted. This preliminary action ensures that the endplate is already distracted and stabilized in the correct position, preventing subsequent subsidence while maintaining a simplified single-stage insertion procedure for the cage itself.
Solution Approach 2:
The distraction system transitions from a collapsed low-profile state during insertion to an expanded stable state after insertion. The legs are dynamically expandable, allowing the system to adapt its footprint from small (for minimally invasive insertion) to large (for stable load distribution), thereby maintaining both procedural simplicity and precision in disc space maintenance.
3Reliability
If the trial device is expanded to provide a large footprint for load distribution, then subsidence is reduced, but the device complexity increases
Solution Approach 1:
The four distraction legs are nested within a common body during the collapsed state, creating a compact low-profile device for minimally invasive insertion. After insertion, the legs are expanded outward from the body to form the large footprint needed for load distribution. This nesting approach provides a large functional footprint when needed while minimizing device complexity and size during insertion.
4Length of stationary object
If the distraction system is expanded vertically to distract the intervertebral space, then the disc space is opened, but the system length contracts which may affect measurement accuracy
Solution Approach 1:
The distraction legs incorporate measurement indicators that provide feedback on the actual disc space distraction achieved. These indicators allow the surgeon to verify the expanded height and select the appropriately sized fusion cage based on real-time feedback from the distracted state, ensuring measurement precision despite any contraction that occurs during the expansion process.
Data Source
AI summary
Systems and methods for distracting an intervertebral disc space are provided. The systems use an expandable trial with telescopic stabilizers. The systems and methods of distracting an intervertebral space are provided in a manner that addresses the problem of subsidence. The method includes inserting the trial into the intervertebral space in a collapsed state and, once inserted, the trial is then used for distracting the intervertebral space using an expansion that includes a first stage and a second stage. The first stage includes expanding the trial laterally toward the peripheral zones of the top vertebral plate and the bottom vertebral plate, and the second stage includes expanding the trial vertically to distract the intervertebral space.