Bone Anchor Closure Thread Angle Design
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Solution Overview
Problem
Conventional threaded connections for bone anchors in spinal fixation are difficult and expensive to manufacture, and they often lead to deformation and splaying of the bone anchor during tightening.
Innovation Solution
A bone anchor assembly with a receiver member and a closure mechanism featuring an outer thread with a thread angle between 5° and 25°, which minimizes lateral transfer of axial tightening force and reduces manufacturing complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional threaded connections are used to secure the spinal fixation element to the bone anchor, then the connection can be achieved, but the manufacturing becomes difficult and expensive, and deformation and splaying of the bone anchor occurs during tightening
Solution Approach 1:
The patent changes the thread angle parameter from conventional values (typically 60° for metric threads) to a reduced range of 5°-25°. This parameter modification allows the thread to function as both a fastening mechanism and a self-centering guide, eliminating the need for complex manufacturing tolerances while reducing lateral forces that cause bone anchor deformation. The altered thread geometry fundamentally changes how the connection is achieved, making it both easier to manufacture and more reliable.
2Stability of the object's composition
If conventional threaded connections with minimal lateral force transfer are designed, then bone anchor deformation is minimized, but the thread design becomes complex and expensive to manufacture
Solution Approach 1:
The reduced angle thread design performs multiple functions simultaneously: it provides fastening, self-centering, and force distribution. The same thread geometry that secures the spinal fixation element also guides the closure mechanism and distributes axial load to minimize lateral forces on the bone anchor. This multi-functionality eliminates the need for separate complex features, simplifying the overall design while maintaining bone anchor stability.
3Ease of manufacture
If a threaded connection design is simplified for easier manufacture, then manufacturing cost decreases, but the ability to minimize lateral transfer of axial tightening force may be compromised
Solution Approach 1:
By changing the thread angle parameter to 5°-25°, the patent achieves a thread design that is simpler to manufacture (closer to standard threading processes) while simultaneously improving force distribution. The shallow angle allows the thread to engage more gradually, distributing the axial tightening force over a longer engagement length and reducing peak lateral forces, all while maintaining manufacturing simplicity.
Data Source
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AI summary
A bone anchor assembly includes a bone anchor, a receiver member for receiving a spinal fixation element to be coupled to the bone anchor, and a closure mechanism. The closure mechanism is positionable between the arms of the receiver member to capture a spinal fixation element within the receiver member and fix the spinal fixation element with respect to the receiver member. The closure mechanism includes an outer thread engageable with an inner thread on the arms of the receiver member. The inner thread and the outer thread have a thread angle between 5° and 25°.