Expandable Spinal Spacer With Graft Window And End-Locking Mechanism
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Solution Overview
Problem
Conventional spinal spacers used in corpectomy cases lack a graft window, requiring bone graft to be inserted before expansion, resulting in unfilled space in the expanded cage.
Innovation Solution
A spinal spacer with a variable axial height and a graft window, featuring a set screw and pressure plate locking mechanism that allows for expansion without rotating the cage components, enabling graft insertion after expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a graft window is added to the spacer, then bone graft can be inserted after expansion, but the locking mechanism must be relocated or the graft window must be made very small
Solution Approach 1:
The patent relocates the locking mechanism from the lateral view to the end view of the spacer, utilizing a different spatial dimension. The set screw and pressure plate are positioned on the end surface of the inner member, allowing the graft window to be located on the lateral surface without interference. This dimensional repositioning resolves the conflict between needing a large graft window and having a functional locking mechanism.
2Device complexity
If conventional threaded connection is used to expand the spacer, then the structure is simple, but rotation of the members rotates the spikes and risks injury to adjacent vertebrae
Solution Approach 1:
The patent replaces the conventional threaded connection mechanism with a set screw and pressure plate system that acts on the end surface of the inner member. This substitution eliminates the rotational motion required for expansion, as the set screw simply advances axially to push the pressure plate against the ratchet notches, thereby eliminating the harmful rotation of spikes that could injure adjacent vertebrae.
3Strength
If set screw and pressure plate mechanism is used, then structural strength is enhanced and only one set screw is needed, but the mechanism is more complex than simple threaded connection
Solution Approach 1:
The patent incorporates a spherical head on the set screw that fits into a corresponding spherical recess in the pressure plate. This curved, spherical interface provides mechanical advantage and load distribution, enhancing the structural strength of the locking mechanism. The spherical geometry allows for self-centering and uniform force distribution, which strengthens the overall cage structure while maintaining a relatively simple single-set-screw design.
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 solution provides a secure and expandable spinal spacer with a graft window, allowing for the insertion of bone graft into the expanded cage, ensuring no unfilled space and enhanced structural strength with only one set screw needed for locking.
Implementation Method 1
ratchet notches provided at its outer wall facing the first member and extending in the axial direction, wherein the first member comprises a wall having an engagement member, which cooperates with the ratchet notches for adjusting the overall height of the spacer
Implementation Method 2
the engagement member comprises i) a set screw and ii) a pressure plate having an outer face contacting the set screw and an inner face having teeth adapted to mate with the ratchet notches of the second member
Data Source
AI summary
An instrument set for an intervertebral expandable spacer having a pair of co-axial annuluses locked together by an engagement member, the set including an inserter/expander having both a rapid expansion mechanism and a fine tuning expansion mechanism.