Twist-In Receiver Insert Assembly for Polyaxial Bone Anchors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing bone screws with fixed heads make it difficult to position a rod or other longitudinal connecting member within the receiver, as the rod must be favorably positioned before insertion, which can be challenging or impossible in certain spinal surgery applications.
Innovation Solution
A polyaxial bone anchor assembly with a receiver, shank, and expandable retainer that allows for a non-tapered locking engagement, providing a friction fit and adjustable connection between the shank and receiver, enabling easy alignment and secure fixation of the connecting member.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a fixed head bone screw is used, then the structure is simple and manufacturing is easy, but the rod cannot be positioned flexibly and alignment is difficult
Solution Approach 1:
The bone screw incorporates a polyaxial mechanism that allows the head to rotate and pivot relative to the shank, transforming a static fixed structure into a dynamic adjustable one. This enables the rod receiver to be positioned at multiple angles and orientations, providing flexibility in rod placement while maintaining a relatively simple overall screw structure.
Solution Approach 2:
The screw is divided into separable components including the shank, head, and retainer mechanism, allowing the head to be independently adjusted relative to the shank. This segmentation enables flexible positioning of the rod receiver without requiring complete redesign of the entire screw structure.
2Ease of operation
If the rod must be favorably positioned before insertion, then the connection is secure, but the alignment process becomes difficult or impossible
Solution Approach 1:
The polyaxial mechanism is pre-configured in the screw head, allowing the surgeon to adjust and position the rod receiver at the desired angle and orientation before inserting the rod. This preliminary adjustment capability eliminates the need for precise pre-positioning of the rod itself, making alignment much easier while maintaining secure connection.
Solution Approach 2:
The retainer mechanism automatically locks into place when the rod is inserted, self-adjusting to maintain the desired angular relationship between the shank and rod receiver. This self-locking feature simplifies the alignment process by eliminating the need for complex manual positioning procedures.
3Adaptability or versatility
If a polyaxial mechanism is added, then rod positioning flexibility is improved, but the assembly complexity increases
Solution Approach 1:
The polyaxial mechanism provides multi-directional angular adjustment capability, allowing the rod receiver to be positioned at various angles relative to the shank. This dynamic adjustability is achieved through a relatively compact retainer and head design, managing complexity while maximizing versatility.
Solution Approach 2:
The polyaxial mechanism serves multiple functions: it allows angular adjustment, maintains secure connection, and enables easy assembly. By integrating these functions into a single mechanism, the design avoids the need for separate components for each function, thereby managing overall 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 assembly facilitates easy alignment and secure fixation of the connecting member, ensuring a stable and adjustable spinal alignment without the need for precise initial positioning, enhancing the usability and effectiveness of spinal surgery procedures.
Implementation Method 1
The retainer is in a non-tapered locking engagement with the shank upper portion when the shank is in a locked orientation with respect to the receiver
Data Source
AI summary
A method of assembling a receiver assembly includes positioning a retainer and an insert into a through-space of a receiver that extends between a bottom opening and an upper opening, such that a second channel of the insert is in non-alignment with a first channel of the receiver. The through-space includes at least one integral downward facing surface and an integral inward projecting surface. The insert includes side structures for contacting internal surfaces of the through-space of the receiver. The method further includes rotating the insert within the through-space of the receiver so as to align the second channel with the first channel for receiving a rod, to move the side structures of the insert into an overlapping arrangement with the inward projecting surface of the through-space that maintains substantial alignment between the second channel and the first channel, and to move one or more upward facing surfaces of the insert into contact with the one or more integral downward facing surfaces of the receiver that limits the insert from moving towards the upper opening in the receiver.