Worm-Gear Expandable Implant for Controlled Spinal Distraction
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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 worm gear mechanism that includes a shaft, end plate, locking mechanism, and gear sleeves, allowing controlled expansion and contraction with a ratchet-like engagement to prevent back-driving, and features such as textured surfaces and pores for bone integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If expandable fusion devices are used to provide distraction force and expand vertebral foramen, then nerve compression is prevented and fusion is aided, but the device risks over-expansion and collapse after implantation
Solution Approach 1:
The device employs a dynamic locking mechanism with a pawl and ratchet tooth system that allows controlled expansion in one direction while preventing collapse in the opposite direction. The pawl can be engaged or disengaged from the ratchet tooth depending on the direction of force applied, creating asymmetric mechanical behavior that ensures stability after implantation.
Solution Approach 2:
The locking mechanism is designed as a separate, extractable component that can be removed or adjusted after implantation if needed. The pawl and ratchet system can be independently engaged or disengaged, allowing post-implantation adjustments or retrieval if complications arise.
2Ease of operation
If expandable devices are designed with small profile for minimally invasive insertion, then surgical approach is simplified, but significant force is required for expansion
Solution Approach 1:
The expandable device features a curved or angled distal end that facilitates navigation through the intervertebral space and alignment with the vertebral bodies. The curved geometry allows the device to be inserted through a minimally invasive approach while the expansion force is distributed along the curved surface, reducing peak stress requirements.
Solution Approach 2:
The device is divided into multiple segments including the body, end plate, and locking mechanism as separate components that can be assembled or inserted sequentially. This segmentation allows for easier minimally invasive insertion while maintaining the structural integrity needed to withstand expansion forces.
3Reliability
If the locking mechanism is engaged to prevent back-driving, then the expanded position is maintained, but friction and resistance force increase
Solution Approach 1:
The locking mechanism uses a dynamic pawl-ratchet engagement that only activates in one direction. During expansion, the pawl is disengaged allowing free movement with minimal resistance. Once the desired position is reached, the pawl engages with the ratchet tooth to prevent back-driving, creating a state where maintenance force is high but expansion force remains low.
Solution Approach 2:
The locking mechanism operates periodically - the pawl engages and disengages based on the direction of applied force. During the expansion phase, the pawl is disengaged; during the maintenance phase, the pawl is engaged. This periodic action allows the device to switch between low-resistance expansion and high-resistance position maintenance.
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 contraction, reducing the risk of spinal instability and facilitating proper fusion by applying a distraction force effectively while minimizing friction and maintaining the expanded position.
Implementation Method 1
rotation of the shaft translates the end plate with respect to the body
Implementation Method 2
The device provides controlled expansion and contraction, reducing the risk of spinal instability and facilitating proper fusion by applying a distraction force effectively
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 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
Implementation Method 5
The expandable may further comprise a spring applying a spring force to the locking mechanism
Implementation Method 6
At least one of the end plate and the body may include a textured surface. At least one of the end plate and the body may include a plurality of pores
Data Source
AI summary
An expandable device comprising, a body defining a bore, a shaft received in the bore of the body, an end plate coupled to the shaft, wherein rotation of the shaft translates the end plate with respect to the body, and 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.