Expandable Intervertebral Spacer Bilateral Hinge Mechanism
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Solution Overview
Problem
Current interbody devices for spinal fusion have limited expansion directions, leading to subsidence where the device collapses through the vertebral endplate, inadequate load-bearing surfaces, and migration issues, which can result in loss of support, pain, and complications in postoperative recovery.
Innovation Solution
An expandable interbody device with a cage structure that includes anterior, posterior, and lateral spacers, connected by hinge members and an actuator, allowing for expansion to securely engage with the cortical bony rim of the vertebral endplates, and optional screw plate and bone screws for fixation to prevent migration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the interbody device is made expandable to increase load-bearing surface area, then the device can better support vertebral bodies and reduce subsidence, but the device complexity increases due to expansion mechanisms
Solution Approach 1:
The interbody device is divided into multiple expandable segments or struts that can independently expand to increase the load-bearing surface area. This segmentation allows the device to achieve larger contact area with vertebral bodies while maintaining a compact form for minimally invasive insertion, resolving the contradiction between surface area and device complexity.
Solution Approach 2:
The expandable interbody device employs a nested structure where smaller components are contained within larger ones in the collapsed state. Upon deployment, these nested components expand outward to provide increased load-bearing surface area. This nesting principle allows the device to transition from a compact insertable form to a larger load-bearing structure, addressing both the need for large contact area and minimally invasive insertion.
2Reliability
If the interbody device contacts predominantly the cancellous portion of the vertebral endplate to facilitate fusion, then bone growth is promoted, but the risk of subsidence increases due to softer bone material
Solution Approach 1:
The interbody device features non-uniform contact surfaces with different local properties. Certain regions are designed to contact the cancellous bone to promote fusion, while other regions with enhanced structural support contact the cortical rim to prevent subsidence. This local differentiation of contact qualities allows the device to simultaneously achieve fusion capability and subsidence resistance.
Solution Approach 2:
The expandable structure of the interbody device provides beforehand cushioning by allowing controlled expansion to distribute loads before subsidence can occur. The device can be expanded to optimize contact distribution across the endplate, creating a cushioning effect that protects against subsidence while maintaining fusion-promoting contact with cancellous bone regions.
3Object-affected harmful factors
If the interbody device is inserted in a collapsed state for minimally invasive surgery, then surgical exposure and infection risk are reduced, but the device cannot provide adequate spacing and support until expanded
Solution Approach 1:
The interbody device transitions from a static collapsed state during insertion to an expandable dynamic state after placement. This dynamic capability allows the device to be inserted minimally invasively in a compact form and then expanded in situ to provide the necessary spacing and support, resolving the contradiction between minimally invasive insertion and immediate functional capability.
Solution Approach 2:
The device is prepared in a collapsed state before insertion to enable minimally invasive surgery. After placement in the intervertebral space, the expansion action is performed to achieve the required spacing and support. This preliminary collapsing action allows the device to be inserted through smaller incisions with reduced surgical exposure, while subsequent expansion provides the necessary mechanical function.
4Strength
If the contact area of the interbody device is increased to bear patient loads and expansion loads, then load-bearing capacity improves, but the overall device size increases requiring larger surgical incision
Solution Approach 1:
The interbody device utilizes dimensional transformation by being inserted in a collapsed configuration through a small incision and then expanded in the target site to provide large load-bearing contact area. This dimensional change from compact 3D form to expanded 3D form with larger surface area allows the device to achieve high load-bearing capacity without requiring a proportionally large incision, as the expansion occurs in the spatial dimension after insertion.
Data Source
AI summary
An expandable interbody spacer for intervertebral fusion is provided. The interbody spacer includes an anterior spacer, at least two anterior hinge members having a first end and a second end, a first lateral spacer, a second lateral spacer, at least two posterior hinge members having a first end and a second end, and a posterior spacer. The anterior spacer is operatively coupled to the first ends of the anterior hinge members. The second end of the first anterior hinge member is operatively coupled to the first lateral spacer. The second end of the second anterior hinge member is operatively coupled to the second lateral spacer. The posterior spacer is operatively coupled to the first ends of the posterior hinge members. The second end of the first posterior hinge member is connected to the first lateral spacer. The second end of the second posterior hinge member is connected to the second lateral spacer. The interbody spacer is configured to expand bilaterally in a medial-lateral direction such that the first and second lateral spacers engage the lateral most aspects of the adjacent vertebrae.