Adjustable Pedicle Screw with Telescoping Head
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Solution Overview
Problem
Current spinal implant systems face challenges in providing adjustable stability and preventing bone screw pull-out during spinal correction procedures, leading to issues with micro-motion and cyclic loading, which can result in reduced effectiveness and increased risk of complications.
Innovation Solution
The development of an adjustable height pedicle screw system with a tulip or top loading mechanism that includes a telescoping head and screw shaft, featuring a transverse slot and inner female threads with a slit to prevent micro-motion, and a polymer bushing to absorb motion, along with a counter torque engagement to resist screw pull-out, allowing for flexible adjustment and secure fixation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a fixed-height bone screw is used, then the surgical procedure is simple, but the spinal construct cannot be adjusted during surgery leading to micro-motion and reduced stability
Solution Approach 1:
The bone screw incorporates a telescoping mechanism where the head can move axially relative to the screw shaft within a defined range, allowing height adjustment while maintaining a compact integrated structure. The part connects the head and shaft and enables controlled translation between them.
Solution Approach 2:
The bone screw transitions from a fixed static structure to a dynamic adjustable structure, allowing the head position to be modified during surgery to achieve proper spinal alignment and construct stability.
2Reliability
If a simple bone screw connection is used, then the device is easy to manufacture, but the screw shaft can pull out from the bone due to cyclic loading
Solution Approach 1:
The counter-torque engagement mechanism is designed to resist pull-out forces before they can cause failure. The part includes features that engage with the screw shaft to provide preliminary resistance against cyclic loading and pull-out forces.
Solution Approach 2:
The bone screw utilizes a composite structure combining the screw shaft, head, and part made from materials with different properties to achieve both strength and flexibility, improving resistance to pull-out while maintaining manufacturability.
3Stability of the object's composition
If conventional bone screws are used, then the installation is straightforward, but micro-motion occurs at the bone-screw interface reducing fixation strength
Solution Approach 1:
The polymer bushing is installed beforehand to cushion and absorb micro-motion at the bone-screw interface, protecting the interface from damaging forces while maintaining stable fixation.
Solution Approach 2:
The polymer bushing acts as an intermediary element between the bone screw and bone, absorbing micro-motion and reducing stress concentrations at the interface while maintaining overall stability.
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
This solution enables precise adjustment of spinal constructs during surgery, reduces the risk of bone screw pull-out, and minimizes the effects of micro-motion and cyclic loading, providing stable fixation and reducing the need for rod bending or loss of bone-screw interface strength.
Implementation Method 1
a polymer bushing to absorb motion
Implementation Method 2
a counter torque engagement to resist screw pull-out
Data Source
AI summary
A bone fastener comprises a first member defining an implant cavity. A part is connectable with the first member. A second member is configured to penetrate tissue and includes a mating surface engageable with the part. The part is engageable to selectively translate the implant cavity relative to the second member. Implants, spinal constructs, systems, instruments and methods are disclosed.