Expandable Implant Worm Gear for Controlled, Collapse-Resistant Fusion
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Solution Overview
Problem
Existing expandable intervertebral fusion devices face risks of over-expansion, collapse after implantation, and require significant force for expansion, leading to spinal instability and improper fusion.
Innovation Solution
An expandable device with a shaft, end plate, and locking mechanism that allows controlled rotation and expansion, featuring a worm gear system with ratchet teeth and a spring-actuated locking mechanism to prevent back-driving, ensuring stable expansion and collapse prevention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If expandable devices are used to provide distraction force and expand the vertebral foramen, then nerve compression is prevented and intervertebral fusion is aided, but the risk of over-expansion and compression of other portions of the spine increases
Solution Approach 1:
The worm gear mechanism changes the parameter of expansion control by converting rotational motion into precise linear displacement. The self-locking property of the worm gear maintains the expanded position without requiring continuous force, preventing both under-expansion and over-expansion of the vertebral foramen.
Solution Approach 2:
The ratchet and pawl mechanism provides mechanical feedback by allowing motion in one direction (expansion) while preventing reverse motion (over-expansion). This unidirectional control ensures the device expands to the required extent without compressing other portions of the spine.
2Reliability
If expandable devices are used to provide distraction force, then intervertebral fusion is aided, but the device may collapse after implantation creating spinal instability
Solution Approach 1:
The worm gear mechanism is self-locking due to the friction between the worm and gear teeth, which prevents back-driving. This self-service locking feature maintains the expanded position and prevents collapse without requiring additional power sources or complex locking systems, ensuring long-term spinal stability.
Solution Approach 2:
The ratchet and pawl mechanism provides beforehand protection against collapse by allowing expansion in one direction while mechanically blocking reverse motion. This prevents the device from collapsing after implantation, maintaining spinal stability throughout the fusion process.
3Volume of moving object
If expandable devices are used with small size to fit between two vertebrae, then minimally invasive surgery is enabled, but a great deal of force is required for expansion
Solution Approach 1:
The worm gear mechanism segments the expansion force application by converting a small rotational torque into a large linear expansion force through the gear teeth engagement. This mechanical advantage allows a small device to generate sufficient expansion force despite its compact size designed to fit between vertebrae.
Solution Approach 2:
The gear teeth act as an intermediary between the rotational input and linear expansion output. This mechanical intermediary amplifies the input force through the gear ratio, enabling a small device to generate the large expansion forces needed while maintaining a compact form factor for minimally invasive insertion.
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 device provides controlled expansion and collapse, reducing the risk of spinal instability and improving fusion stability by maintaining the desired position without additional locking mechanisms, enhancing surgical efficiency and safety.
Implementation Method 1
rotation of the shaft translates the end plate with respect to the body
Implementation Method 2
expanding the expandable device can require a great deal of force given the weight compressing on the intervertebral device
Implementation Method 3
a locking mechanism engaged with the shaft so as to permit the shaft to rotate in a first direction and apply a resistance force to resist the shaft when attempting to rotate in a second direction
Implementation Method 4
The expandable may further comprise a spring applying a spring force to the locking mechanism
Implementation Method 5
The cap may be tapered with a first taper angle and the locking mechanism may be tapered with a second taper angle, the second taper angle being more acute than the first taper angle such that the locking mechanism applies the resistance force to the cap
Data Source
AI summary
An expandable device comprises a body defining a bore, a shaft received in the bore of the body, an end plate coupled to the shaft. Rotation of the shaft translates the end plate with respect to the body. A locking mechanism is engaged with the shaft so as to permit the shaft to rotate in a first direction and apply a resistance force to resist the shaft when attempting to rotate in a second direction. A method of using the expandable device is also disclosed.