Expandable Spinal Fusion Cage Hinge Design
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Solution Overview
Problem
During posterior interbody fusion procedures, inserting a large enough fusion cage is challenging due to anatomical limitations and risks of nerve root or thecal sac injury, leading to suboptimal lordosis and increased risk of cage migration or retropulsion, with existing solutions either causing complications or having drawbacks.
Innovation Solution
An expandable spinal implant with a 'living hinge' design and wedge-like expansion mechanism that allows for adjustable lordosis, incorporating a PEEK polymer material and asymmetrical hinge axis for oblique trajectories, along with specialized surgical instruments for precise expansion and distraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a larger fusion cage is inserted to achieve desired lordosis and prevent migration, then the lordosis and stability are improved, but the risk of nerve root injury, thecal sac injury, and vertebral endplate fracture increases
Solution Approach 1:
The fusion cage is divided into two separable portions (first portion and second portion) connected by a hinge portion. This segmentation allows the cage to be inserted in a collapsed or partially expanded state through the posterior access, and then expanded to the desired larger size within the disc space, achieving both safe insertion and stable final positioning
Solution Approach 2:
The fusion cage transitions from a static inserted state to a dynamic expanded state. The cage is inserted in a compact configuration and then dynamically expanded within the disc space to achieve the desired lordosis and stability, allowing the structure to change size without requiring a larger initial access pathway
2Object-affected harmful factors
If a properly sized fusion cage is inserted through posterior access, then the risk of nerve root injury is reduced, but the cage becomes loose in the anterior portion and may migrate or retropulse
Solution Approach 1:
The cage is segmented into two portions that can be inserted separately or together in a collapsed state, allowing passage through the safe posterior access pathway. Once positioned, the segments are expanded to fill the entire disc space including the anterior portion, ensuring proper fit and stability without requiring aggressive impaction
Solution Approach 2:
The cage transitions from a compact inserted configuration to an expanded final configuration. This dynamic expansion allows the cage to be inserted through the limited posterior access safely, then expanded within the disc space to achieve proper anterior-posterior fit and stability without migration or retropulsion
3Reliability
If a larger fusion cage is inserted through aggressive impaction to ensure proper fit, then the cage stability is improved, but the risk of vertebral endplate fracture and implant subsidence increases
Solution Approach 1:
The segmented cage design allows the structure to be inserted in a collapsed state and then expanded gradually within the disc space. This eliminates the need for aggressive impaction forces, as the cage self-expands to fit the disc space dimensions, ensuring proper stability without compromising the vertebral endplates
Solution Approach 2:
The dynamic expansion mechanism allows the cage to transition from a compact inserted state to an expanded stable state without requiring aggressive impaction. The gradual expansion within the disc space ensures proper fit and stability while avoiding the harmful forces that could cause endplate fracture or implant subsidence
Data Source
Figure 1A~1C
Figure 2A~2C
Figure 3A~3C
AI summary
An expandable fusion cage system includes an expandable fusion cage having an upper portion, a lower portion, and a hinge portion coupling the lower portion and the upper portion at their distal ends. Positioned between the upper and lower portions is an expansion element that when moved in the proximal direction causes the cage to expand at its proximal end. The system can also include inserter instruments, expandable distraction instruments, and bone funnels.