Polyaxial Bone Screw Retainer Assembly via Pin Locking
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Solution Overview
Problem
Existing polyaxial bone screws face difficulties in assembly and handling due to the complexity of placing retainer pieces in the correct position, which can lead to misplacement and increased time for assembly, and the non-spherical shank head design causes articulation issues between retainer pieces and the receiver.
Innovation Solution
A bone anchoring device with a receiver having a top portion and a base with a seating surface, a retainer structure comprising discrete retaining members, and an insert that frictionally engages the connection head, allowing for bottom-loading of the connection head and providing a broad range of anchoring part sizes without enlarging the receiver, along with a pin mechanism to secure the retaining members and prevent disengagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If retainer pieces are placed in the receiver before assembly, then the connection head can be properly positioned, but the assembly process becomes complex and time-consuming
Solution Approach 1:
The retainer pieces are pre-positioned in the receiver before the connection head is inserted. This preliminary action ensures proper positioning without requiring complex assembly steps later, as the retainers are already in place to guide and secure the connection head during insertion
Solution Approach 2:
The retainer pieces are nested within the receiver structure, fitting into designated slots or cavities. This nesting arrangement allows the retainers to be compactly stored in the receiver before assembly, simplifying the overall assembly process while maintaining precise positioning capability
2Adaptability or versatility
If the receiver size is increased to accommodate larger anchoring parts, then a broader range of anchoring part sizes can be accepted, but the device dimensions increase
Solution Approach 1:
The receiver is segmented into modular components, allowing the internal configuration to be adjusted for different anchoring part sizes without changing the overall external dimensions. The segmented structure enables flexible accommodation of various anchoring part diameters while maintaining a compact receiver footprint
Solution Approach 2:
The receiver features locally varied internal geometry with specific regions optimized for different anchoring part sizes. The internal cavity or seating area has adjustable local dimensions that can accommodate a range of anchoring part diameters, while the external receiver dimensions remain constant
3Ease of operation
If the connection head is freely movable through the receiver opening, then assembly is simplified, but the connection head may become disengaged
Solution Approach 1:
The retainer pieces act as intermediary elements between the connection head and the receiver. During assembly, the retainers guide the connection head into proper position and maintain engagement. The retainers are positioned to allow free movement during insertion but then secure the connection head in place, preventing disengagement while simplifying the assembly process
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 simplifies the assembly process by allowing the retainer to be compactly loaded into the receiver, securely capturing the connection head, and enables rotation until a desired position is achieved, improving mechanical behavior and reducing the risk of disengagement, thus enhancing the usability and stability of the bone anchoring device.
Implementation Method 1
an insert disposed within the receiver and configured to frictionally engage the connection head
Data Source
AI summary
A bone anchoring device for securement to a bone. The device includes an anchor, a receiver, a retainer and an insert. The receiver includes a seating surface defining a cavity communicating with the exterior of the receiver through a first opening configured to receive the connection head of the anchor therethrough. The retainer includes at least two discrete retaining members configured to engage with the receiver seating surface when they are captured between the connection head and the seating surface. The insert is disposed within the receiver and configured to frictionally engage the connection head. The insert includes a main body and at least one pin protruding from the main body, for circumferential insertion between two adjacent retaining members of the retainer.