Bone Anchor Insertion Instrument with Offset Drive Shaft
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Solution Overview
Problem
Existing instruments for inserting bone anchors lack a secure and precise mechanism to align and hold the bone anchor correctly, leading to potential play and misalignment during insertion, which can complicate the stabilization process.
Innovation Solution
The instrument features a holding member with a seat for the bone anchor head that can assume two configurations, allowing precise alignment and secure engagement via a drive shaft with an offset center, eliminating play and ensuring robust connection, and includes a displacement member to automatically align the bone anchor with the drive shaft.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the drive shaft directly engages the bone anchor head without offset, then the structure is simpler, but play exists between the drive shaft and bone anchor leading to misalignment
Solution Approach 1:
The patent applies asymmetry by offsetting the center of the drive shaft from the center of the bone anchor head. This asymmetric positioning creates a specific geometric relationship where the drive shaft center is deliberately displaced from the head center, enabling the head to press against the abutment surface and eliminating play between components, thereby achieving precise alignment without requiring complex additional mechanisms.
Solution Approach 2:
The abutment surface acts as an intermediary element between the bone anchor head and the drive shaft. By positioning the drive shaft offset from the head center, the head is forced to press against this intermediary abutment surface, which mediates the connection and eliminates gaps or play, ensuring robust and precise engagement.
2Reliability
If the holding member uses a simple grip mechanism, then the device is easier to operate, but the connection between the instrument and bone anchor is not robust
Solution Approach 1:
The patent merges multiple functions into the holding member structure. The holding member not only grips the bone anchor head but also incorporates the abutment surface that eliminates play, and works in conjunction with the offset drive shaft to provide both secure holding and precise alignment. This integration of multiple functions into a unified structure achieves robust connection without significantly complicating operation.
3Manufacturing precision
If the seat center is aligned with the drive shaft center, then the structure is more symmetric and simpler, but play exists causing imprecise insertion
Solution Approach 1:
The patent deliberately introduces asymmetry by offsetting the seat center from the drive shaft center. This asymmetric geometric configuration ensures that when the bone anchor head is inserted, its center cannot coincide with the drive shaft center, forcing the head to press against the abutment surface. This eliminates play and ensures precise insertion without requiring complex additional alignment mechanisms.
Data Source
AI summary
An instrument for holding and inserting a bone anchor into a bone is provided, where the bone anchor includes a shank for anchoring in the bone and a head. The instrument includes a holding member for holding the head of the bone anchor and has a plurality of arms configured to at least partially encompass the head, where the arms include an inner surface forming a seat for the head. The instrument also includes a drive shaft for engaging the head of the bone anchor and defining a longitudinal axis of the instrument. The instrument further includes a displacement member configured to act on the holding member. The holding member can assume a first configuration in which it is configured to permit the head to enter the seat and a second configuration in which it is configured to hold the head in the seat.