Polyaxial Bone Anchoring Coupling Assembly Retainer
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Solution Overview
Problem
Existing coupling assemblies for bone anchoring devices face challenges in reliability, durability, and handling, particularly in retaining the head of a bone anchoring element introduced from a bottom opening, with limitations in size and stability.
Innovation Solution
A coupling assembly featuring a radially expandable and compressible retainer element with a locking mechanism that prevents radial expansion, allowing for secure retention of the bone anchoring element's head within the receiving part, while reducing the size of the retainer element and enhancing stability by allowing direct pressure force application from the rod or locking element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional spring chuck or retaining member is used to retain the bone anchoring element head, then the head can be retained in the coupling assembly, but the size of the coupling assembly increases and handling becomes more difficult
Solution Approach 1:
The retainer element is designed as a thin, radially expandable ring or shell structure that can be compressed to a smaller diameter for insertion through the bottom opening, then expanded to retain the bone anchoring element head. This flexible shell approach maintains retention reliability while minimizing the coupling assembly size and improving handling ease.
Solution Approach 2:
The retainer element transitions from a compressed state during insertion to an expanded state during retention, allowing the coupling assembly to adapt its size dynamically. This dynamic behavior enables easy handling during implantation while ensuring secure retention during use.
2Stability of the object's composition
If the retainer element is made large to ensure stable retention of the bone anchoring element head, then retention stability improves, but the coupling assembly size increases and in-situ assembly becomes more difficult
Solution Approach 1:
The retainer element is segmented into radial sections that can expand outward when forced through the bottom opening, allowing the structure to transition from a compact insertion state to a stable retention state. This segmentation enables stable retention without requiring a large initial size, facilitating easier in-situ assembly.
Solution Approach 2:
The retainer element utilizes radial expansion (moving from axial to radial dimension) to achieve stable retention. By expanding in the radial direction after insertion, the retainer element increases its retention capability without increasing the axial length of the coupling assembly, making in-situ assembly easier.
3Reliability
If the retainer element is designed to be radially expandable for secure retention, then retention reliability improves, but the structure becomes more complex
Solution Approach 1:
The retainer element is designed to automatically expand and lock into position when the bone anchoring element head is inserted through the bottom opening. This self-actuating mechanism eliminates the need for separate locking mechanisms or complex actuation systems, maintaining retention reliability while minimizing structural complexity.
Solution Approach 2:
The bone anchoring element head itself serves as the intermediary that drives the radial expansion of the retainer element during insertion. This eliminates the need for separate expansion mechanisms, reducing structural complexity while ensuring reliable retention through the natural insertion force.
4Reliability
If a locking mechanism is added to prevent radial expansion of the retainer element, then retention reliability improves, but the device complexity increases
Solution Approach 1:
The retainer element's radial expansion and locking function is achieved through its own structural design rather than an external locking mechanism. The element expands radially during insertion and naturally locks in place, providing reliable retention without adding mechanism complexity.
Solution Approach 2:
The retainer element combines the functions of retention, expansion, and locking into a single integrated structure. By merging these functions into one component rather than using separate elements, the design achieves high retention reliability while minimizing device complexity.
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 solution improves the reliability and durability of the coupling assembly by ensuring secure retention of the bone anchoring element's head, reducing the size of the retainer element, and enhancing stability, allowing for easier in-situ assembly and increased reliability.
Implementation Method 1
a radially expandable and compressible retainer element with a locking mechanism that prevents radial expansion
Implementation Method 2
allowing for secure retention of the bone anchoring element's head within the receiving part, while reducing the size of the retainer element and enhancing stability by allowing direct pressure force application from the rod or locking element
Data Source
AI summary
A coupling assembly for coupling a rod to a bone anchoring element is provided, wherein the coupling assembly includes a receiving part having a first end, a second end, a central axis extending through the first end and second end, an accommodation space for accommodating a head of an anchoring element, a bore extending from the accommodation space to the first end, and a recess for receiving a rod. The accommodation space has an opening at the second end sized to permit insertion of a head of the bone anchoring element. The coupling assembly further includes a retainer element configured to be positioned at least partially in the accommodation space and being radially expandable and/or compressible to allow retaining a head inserted through the opening. The retainer element is held in position adjacent the opening by an engagement structure provided at or in the accommodation space. The coupling assembly further includes a locking element configured to be arranged at least partially in the accommodation space. The locking element is movable from a first position, in which the retainer element is allowed to expand acid release an inserted head, to a second position, in which radial expansion of the retainer element is hindered to present release of an inserted head. When the locking element is in the second position, a head of an liming element can be locked by exertion of a pressure force directly onto the head to press the head against the retainer element.