Bone Anchoring Device Shank Head Snap Ring
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Solution Overview
Problem
Existing bone anchoring devices with separate shank and head components face challenges in convenient assembly, secure locking, and modular variability, leading to increased stockkeeping costs and complexity.
Innovation Solution
The shank and head are designed as separate parts with a cylindrical interface and optional slits for flexibility, allowing for easy insertion and secure retention, along with a snap ring mechanism for form-locking, enabling variability in shank lengths and applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the shank and head are formed as separate parts, then modular variability and stockkeeping cost reduction are improved, but assembly convenience and secure locking are worsened
Solution Approach 1:
The bone anchoring device is divided into separate shank and head components, allowing independent selection and combination of different shank lengths and types with a common head, thereby achieving modular variability while maintaining assembly simplicity through standardized interfaces
Solution Approach 2:
The shank is inserted into the head component, with the cylindrical end portion of the shank fitting into the cylindrical bore of the head, creating a nested structure that simplifies assembly while enabling modular configuration
2Adaptability or versatility
If the shank and head are formed as separate parts, then modular variability and stockkeeping cost reduction are improved, but secure locking after assembly is worsened
Solution Approach 1:
A snap ring is pre-installed on the shank before assembly, positioned to engage with a groove in the head component, ensuring automatic secure locking occurs immediately upon insertion without requiring additional fastening steps
Solution Approach 2:
The mechanical connection between shank and head is replaced with a form-locking mechanism using the snap ring and groove engagement, which provides secure locking through geometric interlocking rather than traditional mechanical fasteners
3Ease of operation
If a cylindrical interface is used for shank and head connection, then assembly convenience is improved, but secure locking capability is worsened
Solution Approach 1:
While the overall interface is cylindrical for easy insertion, asymmetric features are introduced through the snap ring and groove geometry, creating directional engagement that provides secure locking in the assembled position while maintaining simple insertion
Solution Approach 2:
The cylindrical interface serves multiple functions: it provides simple insertion guidance, maintains concentric alignment during assembly, and works in conjunction with the snap ring to achieve secure locking, thereby combining ease of assembly with reliable connection
Data Source
AI summary
A bone anchoring device includes a shank to be anchored in a bone or vertebra, a head, and a receiving part receiving the head for connecting the shank to a rod. The shank and the head are separate parts. The head has a bore with a cylindrical inner surface, a ring-shaped groove provided on the inner surface, and at least one slit extending from the inner surface to the outer surface of the head. The shank has a first portion for anchoring in the bone or vertebra and a second portion with a cylindrical outer surface adjoining a free end. A projection is provided on the cylindrical outer surface which engages with the ring-shaped groove of the head, when the cylindrical second portion of the shank is inserted in the bore of the head.