Modular Polyaxial Bone Screw with Collet Locking
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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, leading to potential instability 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 of projections and an outer configuration of depressions, and a collet with a resilient base and slots, creating a snap and frictional interference fit to securely lock the tulip head and bone screw, enhancing axial and rotational stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a poly-axial tulip head spine rod bone screw assembly is used, then the spine rod can be held and fixed to vertebrae with various degrees of freedom, but the security and control in locking the orientation of the tulip head relative to the bone screw is insufficient
Solution Approach 1:
The assembly is divided into three separate components: a poly-axial bone screw, a poly-axial tulip head, and an insert forming a collet. This segmentation allows each component to be optimized independently while working together to achieve both versatility in attachment and secure locking of orientation.
Solution Approach 2:
The collet is disposed within the tulip head, creating a nested configuration where the collet interacts with the tulip head to lock axial orientation, and the tulip head interacts with the bone screw head to lock rotational orientation. This nested structure enables multiple locking functions within a compact assembly.
2Reliability
If the collet interacts with the tulip head to lock axial orientation and provides frictional interference fit with the bone screw head, then the orientation locking is improved, but the device complexity increases
Solution Approach 1:
The insert forming a collet is combined with the tulip head through interaction features (projections and depressions) that enable orientation locking. The collet integrates multiple functions: locking axial orientation relative to the tulip head, providing frictional interference fit with the bone screw head, and maintaining structural integrity as a single integrated insert component.
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 design provides a more controlled, uniform, and secure orientation of the tulip head with respect to the bone screw, increasing the surface contact and stability, thereby enhancing the fixation of spinal components during surgical procedures.
Implementation Method 1
The collet also has a resilient, tapered base with a plurality of slots in and about its end that allow the end to elastically splay outwardly over and upon the head of the bone screw to create a snap or frictional interference fit between the splayed collet and the bone screw head
Implementation Method 2
provide a frictional interference fit with the bone screw head in order to lock orientation of the tulip head on and relative to the bone screw
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.