Expandable Intervertebral Cage With Single-Shaft Wedge Adjustment
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Solution Overview
Problem
Existing expandable intervertebral cages face difficulties in actuating adjustment mechanisms, often requiring complex structures, increased dimensions, or fragility due to internal actuation mechanisms, making them difficult to use and potentially unstable.
Innovation Solution
An expandable intervertebral cage with a single central shaft having a mono-directional external thread, combined with proximal and distal wedges and actuators, allows for simultaneous or independent movement of the plates, enabling easy and precise adjustment of spacing and inclination without excessive force, using a compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If adjustment mechanisms are placed in both proximal and distal positions to enable surface inclination variation, then the cage can correct spinal curvature, but the device complexity increases and the implant dimensions must increase to accommodate internal passages
Solution Approach 1:
The patent combines both proximal and distal adjustment mechanisms into a single integrated actuation system. The central shaft with external threading connects both wedges, allowing the surgeon to adjust both proximal and distal plate inclinations simultaneously through one actuator, rather than requiring separate mechanisms at each end.
Solution Approach 2:
The central shaft serves multiple functions: it acts as the actuation mechanism, the structural connector between proximal and distal wedges, and the guide for the adjustment tool. This multi-functional design eliminates the need for separate components, reducing overall device complexity while maintaining full adjustment capability.
2Ease of operation
If the cage dimensions are increased to accommodate internal passages for adjustment tools, then the actuation mechanism can be accessed, but the implant becomes incompatible with anatomical dimensions of the intervertebral space
Solution Approach 1:
The patent positions the actuator at the distal end of the central shaft, making it accessible from the lateral direction rather than requiring access through the intervertebral space. This dimensional change in accessibility allows the adjustment mechanism to be operated without increasing the implant's volume within the constrained anatomical space.
3Volume of moving object
If the implant thicknesses are reduced to maintain global dimensions compatible with intervertebral space, then the implant fits anatomical constraints, but the device becomes fragile or unstable
Solution Approach 1:
The central shaft serves as both the actuation mechanism and a structural reinforcement element. By integrating the shaft through the center of the implant, it provides internal support that strengthens the overall structure without increasing external dimensions, allowing thin-walled construction while maintaining structural integrity.
4Device complexity
If a central hollow shaft with reduced diameter is used to accommodate adjustment tools, then the mechanism can be actuated, but the tool cannot generate sufficient torque to overcome vertebral resistance
Solution Approach 1:
Instead of having the adjustment tool pass through the center of the implant, the patent inverts the approach by positioning the actuator at the distal end of the central shaft. This allows the tool to apply torque directly at the actuation point with maximum leverage, overcoming vertebral resistance without requiring a large central passage.
5Adaptability or versatility
If complex movement mechanisms are used to enable plate adjustment, then the cage can vary surface inclination, but the structure becomes difficult to actuate
Solution Approach 1:
The patent replaces complex mechanical linkage systems with a simplified screw-thread mechanism. The external threading on the central shaft converts rotational motion of the actuator into linear motion of the wedges, providing precise inclination adjustment with minimal actuation force and simplified operation.
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
The cage provides a simple, solid, and compact solution for adjusting vertebral spacing and curvature correction, ensuring stability and ease of use, reducing the risk of tool breakage and allowing precise adjustments.
Implementation Method 1
a single central shaft (5), coaxial with the central longitudinal axis (1a) and having an external thread (5f)... The proximal wedge (6p) and the distal wedge (6d) are aligned along the central longitudinal axis (1a) and are coupled to the external thread (5f) of the central shaft (5)
Implementation Method 2
The proximal wedge (6p) and the distal wedge (6d) have inclined surfaces (6p', 6d') which abut and slide against the inclined planes (15) of the two plates
Data Source
Figure 1~2
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Figure 5~6
AI summary
An expandable intervertebral cage for spacing out two vertebral bodies of a vertebral column comprising a first plate and a second plate opposite to the first one, both having a planar conformation axially elongated along a central longitudinal axis extending from a proximal end to a distal end of the cage. The two plates comprise respective internal surfaces facing each other and respective external contact surfaces, the latter suitable to receive a respective vertebral body for resting. The cage further comprises a movement and adjustment mechanism of the two plates suitable to promote the relative mutual translation between the first and second plate parallel to each other, so as to vary the height of the cage to space out two adjacent vertebral bodies, and the rotation of the one with respect to the other around a respective hinge axis, so as to vary the mutual inclination between the two plates, to correct the deformation of the vertebral column. The movement and adjustment mechanism comprises a single central shaft, coaxial with the central longitudinal axis and having an external thread, a proximal wedge and a distal wedge placed between the first and second plate, aligned along the central longitudinal axis and coupled to the external thread of the central shaft which is centrally inserted in the distal wedge and the proximal wedge. The movement and adjustment mechanism also comprises a first actuator and a second actuator, both provided on the central shaft and placed at the same proximal end of the cage.