Expandable Lumbar Cage Rotating Spreading Element
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Solution Overview
Problem
Existing expandable cages for interbody fusion of lumbar vertebrae are difficult to adjust into the expanded position and lack reliable load transfer and stability, particularly under load, due to complex expansion mechanisms and limited contact surfaces.
Innovation Solution
An expandable cage design featuring a rotatable elongated cylindrical spreading element with integrally connected rectangular plates and radially aligned ribs, which engages in grooves within the arms, providing large contact surfaces for stable load transfer and preventing tilting, with a simple 90° rotation mechanism for easy adjustment between states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a rotatable spreading element is used to expand the cage, then the expansion process becomes easier and faster, but the load-bearing capacity decreases due to limited contact area between the spreading element and the arms
Solution Approach 1:
The spreading element is designed with bearing surfaces that engage with the arms in two perpendicular directions: radially (for expansion) and axially (for load transfer). This dual-dimensional engagement allows the spreading element to provide both easy rotation for expansion and sufficient contact area for load-bearing capacity.
Solution Approach 2:
The spreading element combines different geometric features (cylindrical base body for rotation, rectangular plates for axial engagement, radially oriented ribs for radial expansion) to create a composite structure that simultaneously provides ease of operation and high load-bearing capacity.
2Ease of operation
If the spreading element is rotatable about a simple axis, then the adjustment is simpler and faster, but tilting and twisting of the spreading element cannot be reliably prevented under load
Solution Approach 1:
The spreading element is segmented into distinct functional components: a cylindrical base body for rotation, rectangular plates for axial positioning, and radially oriented ribs for radial expansion. Each segment performs a specific function that collectively prevents tilting and twisting while maintaining simple rotational adjustment.
Solution Approach 2:
The cylindrical base body of the spreading element provides a curved surface that rotates within grooves of the arms. This curved geometry naturally guides the rotation path and prevents tilting, while the grooves constrain the motion to a precise circular path.
3Strength
If the contact area between the spreading element and arms is increased, then the load-bearing capacity improves, but the expansion mechanism becomes more complex
Solution Approach 1:
Multiple functions are merged into the spreading element: the cylindrical base body provides rotation, the rectangular plates provide axial engagement, and the radially oriented ribs provide radial expansion. This merging of functions into a single component increases contact area for load-bearing without adding separate expansion mechanisms.
Solution Approach 2:
The spreading element is designed as a multi-functional component that simultaneously enables expansion, provides load transfer, and prevents tilting. The grooves in the arms serve multiple purposes: guiding radial expansion and providing axial bearing surfaces, thereby simplifying the overall mechanism while maintaining high load-bearing capacity.
4Ease of operation
If the cage is made expandable with lower entry height, then insertion becomes easier, but the expansion adjustment becomes complex and requires considerable skill and dexterity
Solution Approach 1:
The spreading element is designed to be self-guiding during expansion. The grooves in the arms automatically guide the radial and axial movement of the spreading element, eliminating the need for complex external guidance mechanisms or high surgical skill for precise positioning.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables quick and reliable expansion with high load transfer capabilities, preventing displacement and tilting, and allows for easy revision operations with open side walls for better radiological examination.
Implementation Method 1
the ribs and the base body each have paired opposing curved bearing surfaces on their respective outer circumference, which alternatively and depending on the spreading state of the cage engage in corresponding grooves
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The cage (1) has ribs (8) and a rotatable, elongate and cylindrical base body (4) including curved radial contact surfaces (9) at an outer circumference. The contact surfaces alternatively lie for rotatable mounting in corresponding channels (26) based on a spreading condition of the cage. The channels extend in a longitudinal direction of the cage, and are provided at inner sides of lower arms (18). A device for rotatably driving a spreading element (3) is provided in a rear part of the spreading element, where the rear part lies in a bridge-like connection (15) formed at ends of the arms.