Modular Bone Screw Collet Locking Mechanism
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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 spinal rods relative to the bone screw, limiting the precision and stability of spinal fixation.
Innovation Solution
A modular poly-axial bone screw assembly comprising a poly-axial bone screw, a tulip head with an inner configuration of radially projecting projections, and a collet with a resilient, tapered base and slots, creating a snap and frictional interference fit to securely lock the tulip head's orientation relative to the bone screw, enhancing surface contact and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a poly-axial tulip head spine rod holder is used, then the spine rod can be rigidly locked into various positions, but the orientation control and stability of the tulip head relative to the bone screw is insufficient
Solution Approach 1:
The assembly is divided into three separate components: the bone screw, the tulip head, and the collet. This segmentation allows each component to have optimized functions - the bone screw provides anchor fixation, the tulip head provides poly-axial adjustment capability, and the collet provides secure orientation locking through interference fit, thereby resolving the contradiction between versatility and reliability.
Solution Approach 2:
The collet serves as an intermediary component between the bone screw and the tulip head. It creates a frictional interference fit with the bone screw head to lock the tulip head's orientation, while also being locked axially within the tulip head. This intermediary mechanism enhances orientation stability without compromising the poly-axial adjustment capability.
2Device complexity
If the tulip head is directly attached to the bone screw, then the structure is simpler, but the orientation control and uniformity of the attachment is insufficient
Solution Approach 1:
By introducing the collet as a separate component, the system achieves better orientation control precision. The collet's resilient, tapered base with slots allows elastic splaying to create uniform frictional interference fit around the bone screw head, ensuring precise and controlled orientation that cannot be achieved with a direct attachment design.
Solution Approach 2:
The collet utilizes elastic deformation parameter changes - the resilient base with slots allows the material to elastically splay outward when engaged with the bone screw head. This parameter change enables the collet to conform precisely to the screw head geometry, creating uniform frictional interference fit and enhancing orientation control precision.
3Reliability
If a resilient, tapered collet with slots is used, then the surface contact and frictional interference fit are improved, but the device complexity increases
Solution Approach 1:
The complexity is concentrated in the local region of the collet where the resilient, tapered base with slots is positioned to engage with the bone screw head. This localized complexity provides the necessary frictional interference fit and locking security, while the rest of the tulip head structure remains relatively simple and maintains its poly-axial adjustment capability.
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 stability and precision of spinal rod fixation, addressing the limitations of existing assemblies.
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
create a snap or frictional interference fit between the splayed collet and the bone screw head
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A modular polyaxial bone screw (10) includes a polyaxial bone screw (16), a polyaxial tulip head (12) and a collet (14) 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 resilient, tapered base with a plurality of slots (33) in and about its end that allow the end to splay outwardly over and upon the head (22) of the bone screw to create a snap or frictional interference fit between the splayed collet and the bone screw head when a spine rod is fixed in the tulip head.