Geared Cam Expandable Spinal Implant
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Solution Overview
Problem
Existing expandable spinal implants apply excessive and irregular initial expansion forces, often back out of the disc space, lack fine adjustment capabilities, and do not provide reliable engagement with vertebral bodies, and lack configuration diversity at the distal tip.
Innovation Solution
An expandable spinal implant with geared cams that include upper and lower endplates with rack portions, a chassis, yoke, and spur gears, which translate rotational motion into linear expansion, and deployable spikes to prevent backout, along with flaps to prevent bone graft leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If conventional 4-bar or crank slider expansion mechanisms are used, then the implant can be expanded, but excessive and irregular initial expansion force is applied to the disc space
Solution Approach 1:
The patent employs a geared cam mechanism where a rotating cam profile dynamically controls the expansion force applied to the disc space. The cam's varying radius and profile allow the expansion force to be modulated throughout the expansion cycle, providing controlled initial expansion force while maintaining reliability through the mechanical advantage of the gear system.
Solution Approach 2:
The patent changes the geometric parameters of the expansion mechanism by using a cam with a specific profile rather than a conventional 4-bar or crank slider. The cam profile parameters (radius, eccentricity, shape) are optimized to produce the desired expansion force characteristics, transforming the force application pattern from irregular to controlled.
2Force
If conventional expansion mechanisms are used, then the implant can be expanded, but irregular expansion force is applied to the disc space
Solution Approach 1:
The geared cam mechanism provides dynamic control over the expansion process. The cam profile is designed to produce a specific motion pattern that ensures uniform expansion force distribution across the disc space, eliminating the irregularities associated with conventional mechanisms.
Solution Approach 2:
The gear system in the expansion mechanism provides mechanical feedback that ensures smooth and uniform expansion. The interlocking gear teeth maintain precise positional relationships between components, preventing irregular motion and ensuring stable, uniform expansion force application throughout the expansion cycle.
3Ease of operation
If conventional expandable implants are used, then the implant can be inserted and expanded, but they occasionally inadvertently back out of the disc space
Solution Approach 1:
The patent incorporates preliminary anti-backout features in the implant design, such as tapered distal tips and engagement surfaces that prevent backward movement. The geared cam mechanism also includes mechanical stops and locked positions that prevent inadvertent backout, addressing the retention issue before it can occur during normal operation.
4Ease of operation
If conventional expandable implants are used, then the implant can be expanded, but they lack a reliable capability for fine adjustment
Solution Approach 1:
The geared cam mechanism allows for dynamic control of the expansion process, enabling fine adjustments through controlled rotation of the cam. The gear system provides precise mechanical advantage, allowing small rotational inputs to translate into controlled linear expansion movements, achieving fine adjustment capability while maintaining ease of 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 implant achieves controlled and stable expansion with reliable engagement to vertebral bodies, preventing backout and ensuring secure positioning, while allowing for fine adjustment and diverse configurations.
Implementation Method 1
At least one first spur gear is rotatably mounted on a distal end of one of the first and second walls of the yoke. The at least one first spur gear has teeth configured to engage the downwardly-projecting teeth of the upper rack portion. At least one second spur gear is rotatably mounted on a distal end of one of the first and second walls of the yoke. The at least one second spur gear has teeth configured to engage the upwardly-projecting teeth of the lower rack portion.
Implementation Method 2
The rotating portion is configured to translate rotational motion thereof to linear motion of the yoke. The yoke translates the linear motion to rotation of the spur gears with respect to the yoke, causing the spur gears to walk along the upper rack gear teeth and lower rack gear teeth, respectively
Implementation Method 3
When the implant is in the fully-expanded position, the distal edges of the spikes engage the upper and lower vertebral bodies. This engagement prevents the implant from inadvertently backing out of the disc space.
Data Source
AI summary
A geared cam expandable spinal implant. Rotational motion of a rotating portion is translated into linear motion of a yoke, which moves geared cams at the distal end of the implant to mate with, and walk along, teeth of corresponding racks. The walking of the gear cam teeth along the rack teeth creates a regular rate of implant expansion, reduces initial excessive expansion force applied to the implant, and provides fine adjustment of the expansion rate and force. Spikes, pivotally mounted on the yoke, pivot outward as the implant expands, to a fully-deployed position into engagement with surfaces of adjacent vertebral bodies. The engagement between the deployed spikes and the vertebral bodies prevents inadvertent backout of the expanded implant.