Geared Cam Interbody Implant With Rack Teeth for Controlled Expansion
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Solution Overview
Problem
Existing expandable spinal implants apply excessive, irregular expansion forces to the disc space, lack fine adjustment capabilities, and often have inadequate configurations at the distal tip for engaging with vertebral bodies.
Innovation Solution
An expandable spinal implant with geared cams that include upper and lower rack portions with projecting teeth, a chassis, a yoke, and spur gears, allowing controlled expansion from a collapsed to a fully-expanded position, using a rotating mechanism to translate rotational motion into linear motion for precise adjustment.
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 from collapsed to expanded position, but excessive and irregular expansion force is applied to the disc space
Solution Approach 1:
The patent replaces conventional 4-bar or crank slider expansion mechanisms with a rack and pinion gear system. This mechanical substitution provides more controlled and uniform expansion force through the engagement of gear teeth with rack teeth, eliminating the excessive and irregular forces characteristic of the previous mechanical systems.
Solution Approach 2:
The gear and rack mechanism inherently provides feedback through the meshing teeth, which engage and disengage in a controlled sequence. This feedback mechanism ensures that expansion force is applied uniformly and allows for precise control of the expansion process, preventing excessive force application.
2Ease of operation
If conventional expansion mechanisms are used, then the implant can be expanded, but fine adjustment capability is lacking
Solution Approach 1:
The patent introduces a gear and rack mechanism that enables fine adjustment capability through the incremental engagement of gear teeth with rack teeth. Each tooth engagement represents a discrete, controllable increment of expansion, allowing precise adjustment that was not achievable with conventional mechanisms.
3Ease of manufacture
If the implant is designed with standard distal tip configuration, then manufacturing is simplified, but reliable engagement with vertebral bodies is not ensured
Solution Approach 1:
The patent applies local quality by providing different configurations specifically at the distal tip of the implant, including varied tooth patterns and engagement surfaces. This allows the distal tip to be optimized for reliable vertebral body engagement while the rest of the implant maintains simpler manufacturing characteristics.
4Productivity
If the implant is expanded quickly to reduce surgery time, then productivity increases, but excessive initial expansion force is applied
Solution Approach 1:
The gear and rack mechanism enables periodic or staged expansion through controlled rotation, where each gear tooth engagement represents a discrete expansion stage. This allows the surgeon to expand the implant in controlled increments rather than applying excessive force in a single rapid motion, balancing speed with force control.
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 provides controlled, uniform expansion with reliable engagement to vertebral bodies, minimizing initial force and ensuring precise fit, facilitating bone fusion and preventing migration.
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
A portion of the inner surface includes an upper rack portion. The upper rack portion includes downwardly-projecting teeth intermediate the proximal end and the distal end of the upper endplate, and at least one distal-most downwardly-projecting tooth proximate the distal end of the upper endplate.
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.