Modular Poly-Axial Bone Screw With Interference Fit Collet
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Solution Overview
Problem
Current poly-axial tulip head spine rod bone screw assemblies lack sufficient security and control in locking the orientation of the tulip head relative to the bone screw, which can lead to instability and reduced clinical outcomes in spinal fixation procedures.
Innovation Solution
A modular poly-axial bone screw assembly comprising a poly-axial bone screw, a tulip head with an inner configuration that interacts with a collet to lock axial and rotational positions, and a resilient, tapered collet base with slots that create a snap or frictional interference fit with the bone screw head, enhancing surface contact and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a poly-axial tulip head spine rod bone screw assembly is used, then the spine rod can be fixed to the vertebra with poly-axial adjustment capability, but the locking mechanism lacks sufficient security and control in locking the orientation of the tulip head relative to the bone screw
Solution Approach 1:
The locking mechanism is divided into separate functional components: a collet with radial slots that can flex independently, and corresponding protrusions on the tulip head that engage with the slots. This segmentation allows each component to perform its specific function optimally while maintaining overall system reliability.
Solution Approach 2:
The collet is designed with radial slots that allow dynamic flexing and deformation during the locking process. The collet can elastically deform to accommodate misalignment and then lock into position, providing adaptive locking security without requiring a complex rigid mechanism.
2Stability of the object's composition
If the collet is made resilient with slots to create a snap fit, then the surface contact and stability are enhanced, but the manufacturing precision requirements increase
Solution Approach 1:
The collet is designed with specific geometric parameters including radial slots at defined angles and a tapered portion with a specific angle range (5-30 degrees). These parameter specifications allow for standardized manufacturing while achieving the desired snap-fit stability and surface contact.
Solution Approach 2:
The collet incorporates a tapered portion that creates a conical friction fit surface. This curved geometry distributes contact forces over a larger surface area, enhancing assembly stability while being manufacturable using standard machining processes.
3Measurement precision
If the collet interacts with the tulip head to lock axial and rotational positions, then the orientation control is improved, but the device complexity increases
Solution Approach 1:
The locking of axial and rotational positions is achieved through a single integrated collet component that simultaneously engages with multiple features on the tulip head. The radial slots handle axial positioning while the tapered portion handles rotational locking, merging multiple locking functions into one element rather than using separate mechanisms.
Solution Approach 2:
The collet acts as an intermediary element between the tulip head and the bone screw assembly. It translates and distributes the locking forces from the tulip head to the bone screw, providing precise orientation control while simplifying the overall interaction mechanism.
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 modular assembly provides a more secure and controlled locking mechanism for the tulip head relative to the bone screw, enhancing the stability and precision of spinal rod fixation, thereby improving clinical outcomes.
Implementation Method 1
a resilient, tapered collet base with slots that create a snap or frictional interference fit with the bone screw head
Implementation Method 2
a resilient, tapered collet base with slots that create a snap or frictional interference fit
Data Source
AI summary
A modular poly-axial bone screw includes a poly-axial bone screw, a poly-axial tulip head, and a collet disposed within the tulip head, the collet interacting with the bone screw and tulip head providing an interference fit with the bone screw head to lock orientation of the tulip head on and relative to the bone screw. Inner configurations of the tulip head interact with outer configurations of the collet to lock axial and/or rotational position of the collet within and relative to the tulip head, and thus about the bone screw head. The collet also has a base configured to conform to a top of a bone screw, wherein the collet is configured to support the bone screw and the tulip head when a spine rod is fixed in the tulip head.