Bone Anchoring Device Self-Locking Head Shank Mechanism
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Solution Overview
Problem
Existing bone anchoring devices lack a secure pre-fixation mechanism for the head relative to the shank before final locking, and they often require additional components like outer rings or nuts for stabilization.
Innovation Solution
A bone anchoring device with a shank and head as separate parts, featuring a conical end portion and a cooperating recess with a self-locking cone angle between 2 to 10 degrees, allowing for pre-fixation and eliminating the need for external components like outer rings or nuts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the head and shank are connected as a single integrated component, then the structural complexity is reduced, but the ability to adjust and pre-assemble the device is limited
Solution Approach 1:
The bone anchoring device is divided into separate head and shank components that can be pre-assembled together. The head contains a receiving portion with a bore that receives the shank, allowing the components to be connected before implantation. This segmentation enables pre-assembly and adjustment while maintaining relatively simple individual component designs.
2Reliability
If additional components like outer rings or nuts are added for stabilization, then the fixation reliability is improved, but the device complexity increases
Solution Approach 1:
The stabilization and locking functions are merged into the interaction between the head's receiving portion and the shank. The bore in the head receives and secures the shank through friction and geometric interlocking, eliminating the need for separate outer rings or nuts. This integration achieves reliable fixation while maintaining device simplicity.
Solution Approach 2:
The head and shank are designed to self-lock through their geometric interaction. The conical end portion of the shank fits into the cylindrical bore of the head, creating a self-retaining connection that does not require additional locking components. The friction and geometric constraints provide automatic stabilization once assembled.
3Stability of the object's composition
If the head is firmly locked in final position immediately, then the fixation stability is improved, but the ability to adjust polyaxial position is reduced
Solution Approach 1:
The connection between the head and shank transitions from a dynamic, adjustable state to a fixed, stable state. During implantation, the head can rotate and adjust its polyaxial position relative to the shank while locked. Once the desired position is achieved, the connection becomes fixed, providing stable final fixation. This dynamic-to-static transition enables both adjustment and stability.
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 device achieves a secure, self-locking connection between the head and shank, preventing unintentional separation and allowing for compact design without additional stabilization components, facilitating versatile sizing and ease of use during surgery.
Implementation Method 1
a conical end portion and a cooperating recess with a self-locking cone angle between 2 to 10 degrees, allowing for pre-fixation
Implementation Method 2
The device achieves a secure, self-locking connection between the head and shank, preventing unintentional separation
Data Source
AI summary
A bone anchoring device has an anchoring element, a receiving portion, and a pressure element. The anchoring element includes a shank to be anchored in a bone or a vertebra and a head, the head having an exterior surface with a spherical segment-shaped portion. The shank and the head are separate parts. The receiving portion includes a first end, a second end opposite to the first end, a longitudinal axis passing through the two ends, a bore coaxial with the longitudinal axis, and a first region adjacent to the second end for receiving a spherical segment-shaped section of the head. The pressure element exerts pressure on the head to lock the head in the receiving portion. The head has a hollow inner portion to receive a free end portion of the shank and wherein the head and the end portion are formed such that the end portion can be elastically clamped by the head.