Pivotal Bone Anchor Assembly with Resilient Pre-Lock Friction Fit
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Solution Overview
Problem
Existing polyaxial bone screws face challenges in maintaining proper alignment and stability during spinal surgery procedures, particularly with open-ended screws, as the receiver head can be difficult to position relative to the shank, leading to floppy or loose handling during implantation.
Innovation Solution
A bone anchor assembly featuring a shank, receiver, retainer, and compression insert with a press-fit engagement and cam capture mechanism, allowing for temporary frictional holding and subsequent locking, ensuring the shank and receiver remain aligned and stable throughout the procedure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a fixed bone screw with a fixed head or receiver relative to the shank is used, then the structure is simple and easy to manufacture, but the rod receiver head cannot be moved relative to the shank making it difficult or impossible to position the rod favorably
Solution Approach 1:
The bone screw incorporates a polyaxial mechanism that enables dynamic adjustment of the receiver head orientation relative to the shank. The receiver can be rotated and positioned at multiple angles (polyaxial movement) before final locking, allowing favorable positioning of the rod receiver head while maintaining a relatively simple overall structure.
2Ease of operation
If an open-ended polyaxial bone screw is used to allow rotation of the head or receiver about the shank, then the rod can be positioned favorably, but the receiver is difficult to lock or fix in a particular position relative to the shank during the procedure
Solution Approach 1:
The polyaxial bone screw incorporates a self-locking mechanism where the receiver head automatically locks into position relative to the shank through a locking surface or cam mechanism. This self-locking feature ensures reliable fixation without requiring additional locking operations or tools during the surgical procedure, while still allowing pre-positioning adjustment.
3Stability of the object's composition
If bone screws or other bone anchors are used with components that remain within the bone screw and further remain properly aligned during the procedure, then stability is maintained, but the assembly becomes complex with multiple components that must remain aligned
Solution Approach 1:
The bone screw integrates multiple functional components (shank, receiver head, locking mechanism, and alignment features) into a unified assembly where the components are designed to work together as a single unit. The receiver head is directly attached to the shank with integrated locking surfaces, eliminating the need for separate alignment components while maintaining stability throughout the procedure.
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 provides easy handling and manipulation during surgery, ensuring the shank and receiver maintain a desired angle and secure locking, facilitating efficient implantation of longitudinal connecting members.
Implementation Method 1
The retainer and shank upper portion cooperate in such a manner that a partial rotation between the retainer and the shank brings the shank and retainer structures into locking engagement
Implementation Method 2
The press-fit engagement between the shank upper portion and the retainer may also be described as a cam capture, with the retainer and/or shank upper portion having a sloping or inclined surface
Implementation Method 3
The compression insert frictionally engages the shank during assembly, providing non-floppy positioning of the shank with respect to the receiver
Implementation Method 4
The non-floppy temporary frictional holding is provided by at least one resilient surface on the insert, compression of the resilient surface toward the insert during the temporary frictional holding is by an inner surface of the receiver
Implementation Method 5
When the insert is pressed downwardly into locking engagement with the shank upper portion or head, the resilient surface returns to a neutral or near neutral position, resiliently pressing out against the receiver and locking the insert against the receiver
Data Source
AI summary
A pivotal bone anchor assembly is provided that includes a receiver, a shank, and a compression insert. The receiver can have a shank holding lower portion and an upper portion with a channel. The shank can have a head portion and an anchor portion attachable to bone. The compression insert can be positionable with the receiver, and can have an upper portion including at least one notch at least partially formed in an outer surface of the upper portion, and defining at least one resiliently deflectable upwardly-facing surface extending over or above the at least one notch. In one embodiment, the at least one resiliently deflectable upward facing surface being deflectable when the head portion of the shank and the compression insert are positioned in the receiver to provide a pre-lock friction fit in the assembly prior to securing a longitudinal connecting member in the channel with a closure.